diff --git a/simpleperf/ETMDecoder.cpp b/simpleperf/ETMDecoder.cpp
index c110e9f..b077de5 100644
--- a/simpleperf/ETMDecoder.cpp
+++ b/simpleperf/ETMDecoder.cpp
@@ -21,8 +21,7 @@
 #include <llvm/Support/MemoryBuffer.h>
 #include <opencsd.h>
 
-using namespace simpleperf;
-
+namespace simpleperf {
 namespace {
 
 class DecoderLogStr : public ocsdMsgLogStrOutI {
@@ -757,8 +756,6 @@
 
 }  // namespace
 
-namespace simpleperf {
-
 bool ParseEtmDumpOption(const std::string& s, ETMDumpOption* option) {
   for (auto& value : android::base::Split(s, ",")) {
     if (value == "raw") {
diff --git a/simpleperf/IOEventLoop.cpp b/simpleperf/IOEventLoop.cpp
index b87a05d..06bdd71 100644
--- a/simpleperf/IOEventLoop.cpp
+++ b/simpleperf/IOEventLoop.cpp
@@ -21,6 +21,8 @@
 
 #include <android-base/logging.h>
 
+namespace simpleperf {
+
 struct IOEvent {
   IOEventLoop* loop;
   event* e;
@@ -221,3 +223,5 @@
   }
   return true;
 }
+
+}  // namespace simpleperf
diff --git a/simpleperf/IOEventLoop.h b/simpleperf/IOEventLoop.h
index 6f78d78..f019296 100644
--- a/simpleperf/IOEventLoop.h
+++ b/simpleperf/IOEventLoop.h
@@ -24,9 +24,12 @@
 #include <memory>
 #include <vector>
 
+struct event_base;
+
+namespace simpleperf {
+
 struct IOEvent;
 typedef IOEvent* IOEventRef;
-struct event_base;
 
 // IOEventLoop is a class wrapper of libevent, it monitors events happened,
 // and calls the corresponding callbacks. Possible events are: file ready to
@@ -87,4 +90,6 @@
   bool in_loop_;
 };
 
+}  // namespace simpleperf
+
 #endif  // SIMPLE_PERF_IOEVENT_LOOP_H_
diff --git a/simpleperf/IOEventLoop_test.cpp b/simpleperf/IOEventLoop_test.cpp
index 546f0d7..95971ae 100644
--- a/simpleperf/IOEventLoop_test.cpp
+++ b/simpleperf/IOEventLoop_test.cpp
@@ -24,6 +24,8 @@
 
 #include <android-base/logging.h>
 
+using namespace simpleperf;
+
 TEST(IOEventLoop, read) {
   int fd[2];
   ASSERT_EQ(0, pipe(fd));
diff --git a/simpleperf/JITDebugReader.cpp b/simpleperf/JITDebugReader.cpp
index f483c49..3b58407 100644
--- a/simpleperf/JITDebugReader.cpp
+++ b/simpleperf/JITDebugReader.cpp
@@ -39,11 +39,11 @@
 #include "read_elf.h"
 #include "utils.h"
 
+namespace simpleperf {
+
 using android::base::StartsWith;
 using android::base::StringPrintf;
 
-namespace simpleperf {
-
 // If the size of a symfile is larger than EXPECTED_MAX_SYMFILE_SIZE, we don't want to read it
 // remotely.
 static constexpr size_t MAX_JIT_SYMFILE_SIZE = 1024 * 1024u;
diff --git a/simpleperf/ProbeEvents.cpp b/simpleperf/ProbeEvents.cpp
index c09652a..636923f 100644
--- a/simpleperf/ProbeEvents.cpp
+++ b/simpleperf/ProbeEvents.cpp
@@ -33,15 +33,14 @@
 #include "event_type.h"
 #include "utils.h"
 
+namespace simpleperf {
+
 using android::base::ParseInt;
 using android::base::ParseUint;
 using android::base::Split;
 using android::base::StringPrintf;
 using android::base::unique_fd;
 using android::base::WriteStringToFd;
-using namespace simpleperf;
-
-namespace simpleperf {
 
 static const std::string kKprobeEventPrefix = "kprobes:";
 
diff --git a/simpleperf/SampleComparator.h b/simpleperf/SampleComparator.h
index 7c2a53b..e13f234 100644
--- a/simpleperf/SampleComparator.h
+++ b/simpleperf/SampleComparator.h
@@ -21,6 +21,8 @@
 
 #include <vector>
 
+namespace simpleperf {
+
 // The compare functions below are used to compare two samples by their item
 // content.
 
@@ -121,4 +123,6 @@
   std::vector<compare_sample_func_t> compare_v_;
 };
 
+}  // namespace simpleperf
+
 #endif  // SIMPLE_PERF_SAMPLE_COMPARATOR_H_
diff --git a/simpleperf/SampleDisplayer.h b/simpleperf/SampleDisplayer.h
index 0216594..cc27a46 100644
--- a/simpleperf/SampleDisplayer.h
+++ b/simpleperf/SampleDisplayer.h
@@ -25,6 +25,8 @@
 #include <android-base/logging.h>
 #include <android-base/stringprintf.h>
 
+namespace simpleperf {
+
 // The display functions below are used to show items in a sample.
 
 template <typename EntryT, typename InfoT>
@@ -278,4 +280,6 @@
   bool report_csv_ = false;
 };
 
+}  // namespace simpleperf
+
 #endif  // SIMPLE_PERF_SAMPLE_DISPLAYER_H_
diff --git a/simpleperf/build_id.h b/simpleperf/build_id.h
index fabf0fb..05acc26 100644
--- a/simpleperf/build_id.h
+++ b/simpleperf/build_id.h
@@ -21,6 +21,8 @@
 #include <string.h>
 #include <algorithm>
 
+namespace simpleperf {
+
 constexpr size_t BUILD_ID_SIZE = 20;
 
 // Shared libraries can have a section called .note.gnu.build-id, containing
@@ -86,4 +88,6 @@
   return os;
 }
 
+}  // namespace simpleperf
+
 #endif  // SIMPLE_PERF_BUILD_ID_H_
diff --git a/simpleperf/callchain.h b/simpleperf/callchain.h
index 96d1e68..0a9f173 100644
--- a/simpleperf/callchain.h
+++ b/simpleperf/callchain.h
@@ -27,6 +27,8 @@
 
 #include <android-base/logging.h>
 
+namespace simpleperf {
+
 template <typename EntryT>
 struct CallChainNode {
   uint64_t period;
@@ -150,4 +152,6 @@
   }
 };
 
+}  // namespace simpleperf
+
 #endif  // SIMPLE_PERF_CALLCHAIN_H_
diff --git a/simpleperf/cmd_api.cpp b/simpleperf/cmd_api.cpp
index 0bae420..736f239 100644
--- a/simpleperf/cmd_api.cpp
+++ b/simpleperf/cmd_api.cpp
@@ -35,9 +35,9 @@
 #include "utils.h"
 #include "workload.h"
 
-using namespace simpleperf;
-
+namespace simpleperf {
 namespace {
+
 const std::string SIMPLEPERF_DATA_DIR = "simpleperf_data";
 
 class PrepareCommand : public Command {
@@ -207,8 +207,6 @@
 }
 }  // namespace
 
-namespace simpleperf {
-
 void RegisterAPICommands() {
   RegisterCommand("api-prepare", [] { return std::unique_ptr<Command>(new PrepareCommand()); });
   RegisterCommand("api-collect", [] { return std::unique_ptr<Command>(new CollectCommand()); });
diff --git a/simpleperf/cmd_debug_unwind.cpp b/simpleperf/cmd_debug_unwind.cpp
index 481e24f..b2fd1a7 100644
--- a/simpleperf/cmd_debug_unwind.cpp
+++ b/simpleperf/cmd_debug_unwind.cpp
@@ -36,7 +36,8 @@
 #include "utils.h"
 #include "workload.h"
 
-using namespace simpleperf;
+namespace simpleperf {
+namespace {
 
 // Cache size used by CallChainJoiner to cache call chains in memory.
 constexpr size_t DEFAULT_CALL_CHAIN_JOINER_CACHE_SIZE = 8 * 1024 * 1024;
@@ -404,7 +405,7 @@
   printf("Please use debug_unwind_reporter.py to get a report in details.\n");
 }
 
-namespace simpleperf {
+}  // namespace
 
 void RegisterDebugUnwindCommand() {
   RegisterCommand("debug-unwind",
diff --git a/simpleperf/cmd_dumprecord.cpp b/simpleperf/cmd_dumprecord.cpp
index a9f7dba..8e8bcd2 100644
--- a/simpleperf/cmd_dumprecord.cpp
+++ b/simpleperf/cmd_dumprecord.cpp
@@ -36,11 +36,11 @@
 #include "tracing.h"
 #include "utils.h"
 
-using namespace simpleperf;
-using namespace simpleperf::PerfFileFormat;
-
+namespace simpleperf {
 namespace {
 
+using namespace PerfFileFormat;
+
 struct SymbolInfo {
   Dso* dso;
   const Symbol* symbol;
@@ -509,8 +509,6 @@
 
 }  // namespace
 
-namespace simpleperf {
-
 void RegisterDumpRecordCommand() {
   RegisterCommand("dump", [] { return std::unique_ptr<Command>(new DumpRecordCommand); });
 }
diff --git a/simpleperf/cmd_help.cpp b/simpleperf/cmd_help.cpp
index 8f45c62..1c8cd63 100644
--- a/simpleperf/cmd_help.cpp
+++ b/simpleperf/cmd_help.cpp
@@ -22,7 +22,8 @@
 
 #include "command.h"
 
-using namespace simpleperf;
+namespace simpleperf {
+namespace {
 
 class HelpCommand : public Command {
  public:
@@ -86,7 +87,7 @@
   printf("%s\n", command.LongHelpString().c_str());
 }
 
-namespace simpleperf {
+}  // namespace
 
 void RegisterHelpCommand() {
   RegisterCommand("help", [] { return std::unique_ptr<Command>(new HelpCommand); });
diff --git a/simpleperf/cmd_inject.cpp b/simpleperf/cmd_inject.cpp
index d092573..a2b5b09 100644
--- a/simpleperf/cmd_inject.cpp
+++ b/simpleperf/cmd_inject.cpp
@@ -31,8 +31,6 @@
 #include "thread_tree.h"
 #include "utils.h"
 
-using namespace simpleperf;
-
 namespace simpleperf {
 
 std::string BranchToProtoString(const std::vector<bool>& branch) {
@@ -56,8 +54,6 @@
   return branch;
 }
 
-}  // namespace simpleperf
-
 namespace {
 
 using AddrPair = std::pair<uint64_t, uint64_t>;
@@ -512,8 +508,6 @@
 
 }  // namespace
 
-namespace simpleperf {
-
 void RegisterInjectCommand() {
   return RegisterCommand("inject", [] { return std::unique_ptr<Command>(new InjectCommand); });
 }
diff --git a/simpleperf/cmd_kmem.cpp b/simpleperf/cmd_kmem.cpp
index a4ff3d6..9860396 100644
--- a/simpleperf/cmd_kmem.cpp
+++ b/simpleperf/cmd_kmem.cpp
@@ -29,6 +29,7 @@
 #include "tracing.h"
 #include "utils.h"
 
+namespace simpleperf {
 namespace {
 
 struct SlabSample {
@@ -678,8 +679,6 @@
 
 }  // namespace
 
-namespace simpleperf {
-
 void RegisterKmemCommand() {
   RegisterCommand("kmem", [] { return std::unique_ptr<Command>(new KmemCommand()); });
 }
diff --git a/simpleperf/cmd_list.cpp b/simpleperf/cmd_list.cpp
index ceb0401..4966b9c 100644
--- a/simpleperf/cmd_list.cpp
+++ b/simpleperf/cmd_list.cpp
@@ -30,8 +30,7 @@
 #include "event_selection_set.h"
 #include "event_type.h"
 
-using namespace simpleperf;
-
+namespace simpleperf {
 namespace {
 
 enum EventTypeStatus {
@@ -214,8 +213,6 @@
 
 }  // namespace
 
-namespace simpleperf {
-
 void RegisterListCommand() {
   RegisterCommand("list", [] { return std::unique_ptr<Command>(new ListCommand); });
 }
diff --git a/simpleperf/cmd_merge.cpp b/simpleperf/cmd_merge.cpp
index bf2848c..9d41308 100644
--- a/simpleperf/cmd_merge.cpp
+++ b/simpleperf/cmd_merge.cpp
@@ -29,8 +29,7 @@
 #include "thread_tree.h"
 #include "utils.h"
 
-using namespace simpleperf;
-
+namespace simpleperf {
 namespace {
 
 class MergedFileFeature {
@@ -419,8 +418,6 @@
 
 }  // namespace
 
-namespace simpleperf {
-
 void RegisterMergeCommand() {
   return RegisterCommand("merge", [] { return std::unique_ptr<Command>(new MergeCommand); });
 }
diff --git a/simpleperf/cmd_monitor.cpp b/simpleperf/cmd_monitor.cpp
index 06eca5c..6acce4d 100644
--- a/simpleperf/cmd_monitor.cpp
+++ b/simpleperf/cmd_monitor.cpp
@@ -53,12 +53,12 @@
 #include "tracing.h"
 #include "utils.h"
 
+namespace simpleperf {
+namespace {
+
 using android::base::ParseUint;
 using android::base::Realpath;
 using android::base::StringAppendF;
-using namespace simpleperf;
-
-namespace {
 
 struct SymbolInfo {
   Dso* dso;
@@ -592,8 +592,6 @@
 }
 }  // namespace
 
-namespace simpleperf {
-
 void RegisterMonitorCommand() {
   RegisterCommand("monitor", [] { return std::unique_ptr<Command>(new MonitorCommand()); });
 }
diff --git a/simpleperf/cmd_record.cpp b/simpleperf/cmd_record.cpp
index 60677a7..18b8094 100644
--- a/simpleperf/cmd_record.cpp
+++ b/simpleperf/cmd_record.cpp
@@ -64,11 +64,11 @@
 #include "utils.h"
 #include "workload.h"
 
+namespace simpleperf {
+namespace {
+
 using android::base::ParseUint;
 using android::base::Realpath;
-using namespace simpleperf;
-
-namespace {
 
 static std::string default_measured_event_type = "cpu-cycles";
 
@@ -1885,8 +1885,6 @@
 
 }  // namespace
 
-namespace simpleperf {
-
 static bool ConsumeStr(const char*& p, const char* s) {
   if (strncmp(p, s, strlen(s)) == 0) {
     p += strlen(s);
diff --git a/simpleperf/cmd_report.cpp b/simpleperf/cmd_report.cpp
index c77c47b..399e4d8 100644
--- a/simpleperf/cmd_report.cpp
+++ b/simpleperf/cmd_report.cpp
@@ -41,10 +41,11 @@
 #include "tracing.h"
 #include "utils.h"
 
-using android::base::Split;
-
+namespace simpleperf {
 namespace {
 
+using android::base::Split;
+
 static std::set<std::string> branch_sort_keys = {
     "dso_from",
     "dso_to",
@@ -962,8 +963,6 @@
 
 }  // namespace
 
-namespace simpleperf {
-
 void RegisterReportCommand() {
   RegisterCommand("report", [] { return std::unique_ptr<Command>(new ReportCommand()); });
 }
diff --git a/simpleperf/cmd_report_sample.cpp b/simpleperf/cmd_report_sample.cpp
index 32c3ba7..5480847 100644
--- a/simpleperf/cmd_report_sample.cpp
+++ b/simpleperf/cmd_report_sample.cpp
@@ -34,11 +34,11 @@
 #include "thread_tree.h"
 #include "utils.h"
 
-using namespace simpleperf;
-namespace proto = simpleperf_report_proto;
-
+namespace simpleperf {
 namespace {
 
+namespace proto = simpleperf_report_proto;
+
 static const char PROT_FILE_MAGIC[] = "SIMPLEPERF";
 static const uint16_t PROT_FILE_VERSION = 1u;
 
@@ -704,8 +704,6 @@
 
 }  // namespace
 
-namespace simpleperf {
-
 void RegisterReportSampleCommand() {
   RegisterCommand("report-sample",
                   [] { return std::unique_ptr<Command>(new ReportSampleCommand()); });
diff --git a/simpleperf/cmd_stat.cpp b/simpleperf/cmd_stat.cpp
index b913974..6a4fb1a 100644
--- a/simpleperf/cmd_stat.cpp
+++ b/simpleperf/cmd_stat.cpp
@@ -44,11 +44,10 @@
 #include "utils.h"
 #include "workload.h"
 
-using android::base::Split;
-using namespace simpleperf;
-
 namespace simpleperf {
 
+using android::base::Split;
+
 static std::vector<std::string> default_measured_event_types{
     "cpu-cycles",   "stalled-cycles-frontend", "stalled-cycles-backend",
     "instructions", "branch-instructions",     "branch-misses",
@@ -293,8 +292,6 @@
   return "";
 }
 
-}  // namespace simpleperf
-
 namespace {
 
 // devfreq may use performance counters to calculate memory latency (as in
@@ -884,8 +881,6 @@
 
 }  // namespace
 
-namespace simpleperf {
-
 void RegisterStatCommand() {
   RegisterCommand("stat", [] { return std::unique_ptr<Command>(new StatCommand); });
 }
diff --git a/simpleperf/cmd_trace_sched.cpp b/simpleperf/cmd_trace_sched.cpp
index 42c4954..0fcabd2 100644
--- a/simpleperf/cmd_trace_sched.cpp
+++ b/simpleperf/cmd_trace_sched.cpp
@@ -32,11 +32,11 @@
 #include "tracing.h"
 #include "utils.h"
 
-using android::base::StringPrintf;
-using namespace simpleperf;
-
+namespace simpleperf {
 namespace {
 
+using android::base::StringPrintf;
+
 struct SampleInfo {
   uint64_t timestamp;      // the time when the kernel generates the sample
   uint64_t runtime_in_ns;  // the runtime of the thread in the sample
@@ -414,8 +414,6 @@
 
 }  // namespace
 
-namespace simpleperf {
-
 void RegisterTraceSchedCommand() {
   RegisterCommand("trace-sched", [] { return std::unique_ptr<Command>(new TraceSchedCommand()); });
 }
diff --git a/simpleperf/dso.cpp b/simpleperf/dso.cpp
index fbff62b..77a8b15 100644
--- a/simpleperf/dso.cpp
+++ b/simpleperf/dso.cpp
@@ -38,9 +38,10 @@
 #include "read_elf.h"
 #include "utils.h"
 
+namespace simpleperf {
+
 using android::base::EndsWith;
 using android::base::StartsWith;
-using namespace simpleperf;
 
 namespace simpleperf_dso_impl {
 
@@ -947,3 +948,5 @@
   }
   return false;
 }
+
+}  // namespace simpleperf
diff --git a/simpleperf/dso.h b/simpleperf/dso.h
index e8577b2..15a640d 100644
--- a/simpleperf/dso.h
+++ b/simpleperf/dso.h
@@ -31,6 +31,7 @@
 #include "kallsyms.h"
 #include "read_elf.h"
 
+namespace simpleperf {
 namespace simpleperf_dso_impl {
 
 // Find elf files with symbol table and debug information.
@@ -218,4 +219,6 @@
 const char* DsoTypeToString(DsoType dso_type);
 bool GetBuildIdFromDsoPath(const std::string& dso_path, BuildId* build_id);
 
+}  // namespace simpleperf
+
 #endif  // SIMPLE_PERF_DSO_H_
diff --git a/simpleperf/dso_test.cpp b/simpleperf/dso_test.cpp
index 331353f..02958ce 100644
--- a/simpleperf/dso_test.cpp
+++ b/simpleperf/dso_test.cpp
@@ -27,6 +27,7 @@
 #include "thread_tree.h"
 #include "utils.h"
 
+using namespace simpleperf;
 using namespace simpleperf_dso_impl;
 
 TEST(DebugElfFileFinder, use_build_id_list) {
diff --git a/simpleperf/environment.cpp b/simpleperf/environment.cpp
index e373871..e31163b 100644
--- a/simpleperf/environment.cpp
+++ b/simpleperf/environment.cpp
@@ -50,7 +50,7 @@
 #include "utils.h"
 #include "workload.h"
 
-using namespace simpleperf;
+namespace simpleperf {
 
 std::vector<int> GetOnlineCpus() {
   std::vector<int> result;
@@ -915,3 +915,5 @@
   }
   return std::make_pair(major, minor);
 }
+
+}  // namespace simpleperf
diff --git a/simpleperf/environment.h b/simpleperf/environment.h
index 67819d8..1071552 100644
--- a/simpleperf/environment.h
+++ b/simpleperf/environment.h
@@ -37,6 +37,8 @@
 #include "build_id.h"
 #include "perf_regs.h"
 
+namespace simpleperf {
+
 std::vector<int> GetOnlineCpus();
 
 struct KernelMmap {
@@ -138,4 +140,6 @@
 
 const char* GetTraceFsDir();
 
+}  // namespace simpleperf
+
 #endif  // SIMPLE_PERF_ENVIRONMENT_H_
diff --git a/simpleperf/environment_test.cpp b/simpleperf/environment_test.cpp
index 0e89094..8823034 100644
--- a/simpleperf/environment_test.cpp
+++ b/simpleperf/environment_test.cpp
@@ -27,6 +27,7 @@
 #include "thread_tree.h"
 
 namespace fs = std::filesystem;
+using namespace simpleperf;
 
 TEST(environment, PrepareVdsoFile) {
   std::string content;
diff --git a/simpleperf/event_fd.cpp b/simpleperf/event_fd.cpp
index d3eb1f6..0343e15 100644
--- a/simpleperf/event_fd.cpp
+++ b/simpleperf/event_fd.cpp
@@ -38,6 +38,8 @@
 #include "perf_event.h"
 #include "utils.h"
 
+namespace simpleperf {
+
 static int perf_event_open(const perf_event_attr& attr, pid_t pid, int cpu, int group_fd,
                            unsigned long flags) {  // NOLINT
   return syscall(__NR_perf_event_open, &attr, pid, cpu, group_fd, flags);
@@ -322,3 +324,5 @@
 bool IsEventAttrSupported(const perf_event_attr& attr, const std::string& event_name) {
   return EventFd::OpenEventFile(attr, getpid(), -1, nullptr, event_name, false) != nullptr;
 }
+
+}  // namespace simpleperf
diff --git a/simpleperf/event_fd.h b/simpleperf/event_fd.h
index 2112978..90791a5 100644
--- a/simpleperf/event_fd.h
+++ b/simpleperf/event_fd.h
@@ -28,6 +28,8 @@
 #include "IOEventLoop.h"
 #include "perf_event.h"
 
+namespace simpleperf {
+
 struct PerfCounter {
   uint64_t value;         // The value of the event specified by the perf_event_file.
   uint64_t time_enabled;  // The enabled time.
@@ -153,4 +155,6 @@
 
 bool IsEventAttrSupported(const perf_event_attr& attr, const std::string& event_name);
 
+}  // namespace simpleperf
+
 #endif  // SIMPLE_PERF_EVENT_FD_H_
diff --git a/simpleperf/event_selection_set.cpp b/simpleperf/event_selection_set.cpp
index dbf085f..f1e9d3a 100644
--- a/simpleperf/event_selection_set.cpp
+++ b/simpleperf/event_selection_set.cpp
@@ -35,10 +35,10 @@
 #include "tracing.h"
 #include "utils.h"
 
-using android::base::StringPrintf;
-
 namespace simpleperf {
 
+using android::base::StringPrintf;
+
 bool IsBranchSamplingSupported() {
   const EventType* type = FindEventTypeByName("cpu-cycles");
   if (type == nullptr) {
diff --git a/simpleperf/get_test_data.h b/simpleperf/get_test_data.h
index fc3c84c..1ef663b 100644
--- a/simpleperf/get_test_data.h
+++ b/simpleperf/get_test_data.h
@@ -21,6 +21,8 @@
 
 #include "build_id.h"
 
+using BuildId = simpleperf::BuildId;
+
 std::string GetTestData(const std::string& filename);
 const std::string& GetTestDataDir();
 
diff --git a/simpleperf/nonlinux_support/nonlinux_support.cpp b/simpleperf/nonlinux_support/nonlinux_support.cpp
index 65c82d3..823b6e5 100644
--- a/simpleperf/nonlinux_support/nonlinux_support.cpp
+++ b/simpleperf/nonlinux_support/nonlinux_support.cpp
@@ -21,6 +21,8 @@
 #include "environment.h"
 #include "read_dex_file.h"
 
+namespace simpleperf {
+
 bool GetKernelBuildId(BuildId*) {
   return false;
 }
@@ -43,8 +45,6 @@
   return nullptr;
 }
 
-namespace simpleperf {
-
 class NoOpOfflineUnwinder : public OfflineUnwinder {
  public:
   bool UnwindCallChain(const ThreadEntry&, const RegSet&, const char*, size_t,
diff --git a/simpleperf/perf_regs.cpp b/simpleperf/perf_regs.cpp
index 114cb16..cccd136 100644
--- a/simpleperf/perf_regs.cpp
+++ b/simpleperf/perf_regs.cpp
@@ -25,6 +25,8 @@
 
 #include "perf_event.h"
 
+namespace simpleperf {
+
 ArchType ScopedCurrentArch::current_arch = ARCH_UNSUPPORTED;
 
 ArchType GetArchType(const std::string& arch) {
@@ -221,3 +223,5 @@
   }
   return GetRegValue(regno, value);
 }
+
+}  // namespace simpleperf
diff --git a/simpleperf/perf_regs.h b/simpleperf/perf_regs.h
index f5b30aa..17e28a6 100644
--- a/simpleperf/perf_regs.h
+++ b/simpleperf/perf_regs.h
@@ -35,6 +35,8 @@
 
 #include "perf_event.h"
 
+namespace simpleperf {
+
 enum ArchType {
   ARCH_X86_32,
   ARCH_X86_64,
@@ -92,4 +94,6 @@
   bool GetIpRegValue(uint64_t* value) const;
 };
 
+}  // namespace simpleperf
+
 #endif  // SIMPLE_PERF_PERF_REGS_H_
diff --git a/simpleperf/perf_regs_test.cpp b/simpleperf/perf_regs_test.cpp
index c0977b2..fc75cca 100644
--- a/simpleperf/perf_regs_test.cpp
+++ b/simpleperf/perf_regs_test.cpp
@@ -18,6 +18,8 @@
 
 #include <gtest/gtest.h>
 
+using namespace simpleperf;
+
 TEST(RegSet, arch) {
   ArchType arch_pairs[2][2] = {
       {ARCH_X86_32, ARCH_X86_64},
diff --git a/simpleperf/read_apk.cpp b/simpleperf/read_apk.cpp
index aeb2caf..f583839 100644
--- a/simpleperf/read_apk.cpp
+++ b/simpleperf/read_apk.cpp
@@ -33,6 +33,8 @@
 #include "read_elf.h"
 #include "utils.h"
 
+namespace simpleperf {
+
 std::unordered_map<std::string, ApkInspector::ApkNode> ApkInspector::embedded_elf_cache_;
 
 EmbeddedElf* ApkInspector::FindElfInApkByOffset(const std::string& apk_path, uint64_t file_offset) {
@@ -165,3 +167,5 @@
   }
   return false;
 }
+
+}  // namespace simpleperf
diff --git a/simpleperf/read_apk.h b/simpleperf/read_apk.h
index 2296288..baee287 100644
--- a/simpleperf/read_apk.h
+++ b/simpleperf/read_apk.h
@@ -26,6 +26,8 @@
 
 #include "read_elf.h"
 
+namespace simpleperf {
+
 // Container for info an on ELF file embedded into an APK file
 class EmbeddedElf {
  public:
@@ -87,4 +89,6 @@
 bool ParseExtractedInMemoryPath(const std::string& path, std::string* zip_path,
                                 std::string* entry_name);
 
+}  // namespace simpleperf
+
 #endif  // SIMPLE_PERF_READ_APK_H_
diff --git a/simpleperf/read_apk_test.cpp b/simpleperf/read_apk_test.cpp
index 80b58cd..e4dd71f 100644
--- a/simpleperf/read_apk_test.cpp
+++ b/simpleperf/read_apk_test.cpp
@@ -20,6 +20,8 @@
 #include "get_test_data.h"
 #include "test_util.h"
 
+using namespace simpleperf;
+
 TEST(read_apk, FindElfInApkByOffset) {
   ApkInspector inspector;
   ASSERT_TRUE(inspector.FindElfInApkByOffset("/dev/null", 0) == nullptr);
diff --git a/simpleperf/read_dex_file.cpp b/simpleperf/read_dex_file.cpp
index 5644f7f..055a408 100644
--- a/simpleperf/read_dex_file.cpp
+++ b/simpleperf/read_dex_file.cpp
@@ -28,6 +28,8 @@
 #include <android-base/unique_fd.h>
 #include <art_api/dex_file_support.h>
 
+namespace simpleperf {
+
 static bool ReadSymbols(
     const std::vector<uint64_t>& dex_file_offsets, std::vector<DexFileSymbol>* symbols,
     const std::function<std::unique_ptr<art_api::dex::DexFile>(uint64_t offset)>& open_file_cb) {
@@ -96,3 +98,5 @@
                        return dex_file;
                      });
 }
+
+}  // namespace simpleperf
diff --git a/simpleperf/read_dex_file.h b/simpleperf/read_dex_file.h
index 4563b3d..ebddc87 100644
--- a/simpleperf/read_dex_file.h
+++ b/simpleperf/read_dex_file.h
@@ -26,8 +26,10 @@
 #include <art_api/dex_file_support.h>
 #endif
 
+namespace simpleperf {
+
 #ifndef NO_LIBDEXFILE_SUPPORT
-typedef art_api::dex::MethodInfo DexFileSymbol;
+using DexFileSymbol = art_api::dex::MethodInfo;
 #else
 struct DexFileSymbol {
   uint64_t offset;
@@ -43,4 +45,6 @@
                             const std::vector<uint64_t>& dex_file_offsets,
                             std::vector<DexFileSymbol>* symbols);
 
+}  // namespace simpleperf
+
 #endif  // SIMPLE_PERF_READ_DEX_FILE_H_
diff --git a/simpleperf/read_dex_file_test.cpp b/simpleperf/read_dex_file_test.cpp
index 7e72768..3d0e900 100644
--- a/simpleperf/read_dex_file_test.cpp
+++ b/simpleperf/read_dex_file_test.cpp
@@ -24,6 +24,8 @@
 #include "test_util.h"
 #include "utils.h"
 
+using namespace simpleperf;
+
 TEST(read_dex_file, smoke) {
   std::vector<DexFileSymbol> symbols;
   ASSERT_TRUE(ReadSymbolsFromDexFile(GetTestData("base.vdex"), {0x28}, &symbols));
diff --git a/simpleperf/read_elf.cpp b/simpleperf/read_elf.cpp
index ba88d14..2322db6 100644
--- a/simpleperf/read_elf.cpp
+++ b/simpleperf/read_elf.cpp
@@ -41,10 +41,10 @@
 #include "JITDebugReader.h"
 #include "utils.h"
 
-#define ELF_NOTE_GNU "GNU"
-#define NT_GNU_BUILD_ID 3
+namespace simpleperf {
 
-using namespace simpleperf;
+const static char* ELF_NOTE_GNU = "GNU";
+const static int NT_GNU_BUILD_ID = 3;
 
 std::ostream& operator<<(std::ostream& os, const ElfStatus& status) {
   switch (status) {
@@ -130,6 +130,16 @@
   return ElfStatus::NO_ERROR;
 }
 
+bool IsArmMappingSymbol(const char* name) {
+  // Mapping symbols in arm, which are described in "ELF for ARM Architecture" and
+  // "ELF for ARM 64-bit Architecture". The regular expression to match mapping symbol
+  // is ^\$(a|d|t|x)(\..*)?$
+  return name[0] == '$' && strchr("adtx", name[1]) != nullptr &&
+         (name[2] == '\0' || name[2] == '.');
+}
+
+namespace {
+
 struct BinaryWrapper {
   std::unique_ptr<llvm::MemoryBuffer> buffer;
   std::unique_ptr<llvm::object::Binary> binary;
@@ -187,14 +197,6 @@
   return ElfStatus::NO_ERROR;
 }
 
-bool IsArmMappingSymbol(const char* name) {
-  // Mapping symbols in arm, which are described in "ELF for ARM Architecture" and
-  // "ELF for ARM 64-bit Architecture". The regular expression to match mapping symbol
-  // is ^\$(a|d|t|x)(\..*)?$
-  return name[0] == '$' && strchr("adtx", name[1]) != nullptr &&
-         (name[2] == '\0' || name[2] == '.');
-}
-
 void ReadSymbolTable(llvm::object::symbol_iterator sym_begin, llvm::object::symbol_iterator sym_end,
                      const std::function<void(const ElfFileSymbol&)>& callback, bool is_arm,
                      const llvm::object::section_iterator& section_end) {
@@ -306,8 +308,6 @@
   }
 }
 
-namespace {
-
 template <typename T>
 class ElfFileImpl {};
 
@@ -487,8 +487,6 @@
 
 }  // namespace
 
-namespace simpleperf {
-
 std::unique_ptr<ElfFile> ElfFile::Open(const std::string& filename) {
   ElfStatus status;
   auto elf = Open(filename, &status);
diff --git a/simpleperf/read_elf.h b/simpleperf/read_elf.h
index c99350f..bf5cb8b 100644
--- a/simpleperf/read_elf.h
+++ b/simpleperf/read_elf.h
@@ -22,6 +22,12 @@
 #include <string>
 #include "build_id.h"
 
+namespace llvm {
+class MemoryBuffer;
+}
+
+namespace simpleperf {
+
 // Read ELF functions are called in different situations, so it is hard to
 // decide whether to report error or not. So read ELF functions don't report
 // error when something wrong happens, instead they return ElfStatus, which
@@ -55,12 +61,6 @@
   ElfFileSymbol() : vaddr(0), len(0), is_func(false), is_label(false), is_in_text_section(false) {}
 };
 
-namespace llvm {
-class MemoryBuffer;
-}
-
-namespace simpleperf {
-
 struct ElfSegment {
   uint64_t vaddr = 0;
   uint64_t file_offset = 0;
@@ -106,11 +106,11 @@
   ElfFile() {}
 };
 
-}  // namespace simpleperf
-
 bool IsArmMappingSymbol(const char* name);
 ElfStatus IsValidElfFile(int fd, uint64_t file_offset = 0);
 bool IsValidElfFileMagic(const char* buf, size_t buf_size);
 bool GetBuildIdFromNoteSection(const char* section, size_t section_size, BuildId* build_id);
 
+}  // namespace simpleperf
+
 #endif  // SIMPLE_PERF_READ_ELF_H_
diff --git a/simpleperf/read_symbol_map.cpp b/simpleperf/read_symbol_map.cpp
index f40fc2e..15d59e0 100644
--- a/simpleperf/read_symbol_map.cpp
+++ b/simpleperf/read_symbol_map.cpp
@@ -28,7 +28,6 @@
 #include "dso.h"
 
 namespace simpleperf {
-
 namespace {
 
 std::optional<std::string_view> ConsumeWord(std::string_view& content_ref) {
diff --git a/simpleperf/read_symbol_map.h b/simpleperf/read_symbol_map.h
index 733df4a..dea22eb 100644
--- a/simpleperf/read_symbol_map.h
+++ b/simpleperf/read_symbol_map.h
@@ -16,13 +16,13 @@
 
 #pragma once
 
-#include "dso.h"
-
 #include <string>
 #include <vector>
 
 #include <android-base/file.h>
 
+#include "dso.h"
+
 namespace simpleperf {
 
 std::vector<Symbol> ReadSymbolMapFromString(const std::string& content);
diff --git a/simpleperf/read_symbol_map_test.cpp b/simpleperf/read_symbol_map_test.cpp
index 1f66871..234bea8 100644
--- a/simpleperf/read_symbol_map_test.cpp
+++ b/simpleperf/read_symbol_map_test.cpp
@@ -23,9 +23,7 @@
 
 #include "dso.h"
 
-namespace simpleperf {
-
-namespace {
+using namespace simpleperf;
 
 TEST(read_symbol_map, smoke) {
   std::string content(
@@ -56,7 +54,3 @@
   ASSERT_EQ(0x30, symbols[2].len);
   ASSERT_STREQ("three", symbols[2].Name());
 }
-
-}  // namespace
-
-}  // namespace simpleperf
diff --git a/simpleperf/record.cpp b/simpleperf/record.cpp
index c44b6f6..50c31a9 100644
--- a/simpleperf/record.cpp
+++ b/simpleperf/record.cpp
@@ -29,7 +29,7 @@
 #include "tracing.h"
 #include "utils.h"
 
-using namespace simpleperf;
+namespace simpleperf {
 
 static std::string RecordTypeToString(int record_type) {
   static std::unordered_map<int, std::string> record_type_names = {
@@ -1362,3 +1362,5 @@
   auto header = reinterpret_cast<const perf_event_header*>(p);
   return ReadRecordFromBuffer(attr, header->type, p);
 }
+
+}  // namespace simpleperf
diff --git a/simpleperf/record.h b/simpleperf/record.h
index 26a1dbe..db5610f 100644
--- a/simpleperf/record.h
+++ b/simpleperf/record.h
@@ -32,6 +32,8 @@
 #include "build_id.h"
 #include "perf_event.h"
 
+namespace simpleperf {
+
 enum user_record_type {
   PERF_RECORD_USER_DEFINED_TYPE_START = 64,
   PERF_RECORD_ATTR = 64,
@@ -632,4 +634,6 @@
 // own the buffer.
 std::unique_ptr<Record> ReadRecordFromBuffer(const perf_event_attr& attr, char* p);
 
+}  // namespace simpleperf
+
 #endif  // SIMPLE_PERF_RECORD_H_
diff --git a/simpleperf/record_equal_test.h b/simpleperf/record_equal_test.h
index 40157ed..8e27e1e 100644
--- a/simpleperf/record_equal_test.h
+++ b/simpleperf/record_equal_test.h
@@ -14,6 +14,8 @@
  * limitations under the License.
  */
 
+namespace simpleperf {
+
 static void CheckMmapRecordDataEqual(const MmapRecord& r1, const MmapRecord& r2) {
   ASSERT_EQ(0, memcmp(r1.data, r2.data, sizeof(*r1.data)));
   ASSERT_STREQ(r1.filename, r2.filename);
@@ -96,3 +98,5 @@
                                 static_cast<const BuildIdRecord&>(r2));
   }
 }
+
+}  // namespace simpleperf
diff --git a/simpleperf/report_lib_interface.cpp b/simpleperf/report_lib_interface.cpp
index 841d1aa..6f39db4 100644
--- a/simpleperf/report_lib_interface.cpp
+++ b/simpleperf/report_lib_interface.cpp
@@ -31,14 +31,8 @@
 #include "tracing.h"
 #include "utils.h"
 
-using namespace simpleperf;
-
-class ReportLib;
-
 extern "C" {
 
-#define EXPORT __attribute__((visibility("default")))
-
 struct Sample {
   uint64_t ip;
   uint32_t pid;
@@ -100,30 +94,9 @@
   uint32_t data_size;
 };
 
-// Create a new instance,
-// pass the instance to the other functions below.
-ReportLib* CreateReportLib() EXPORT;
-void DestroyReportLib(ReportLib* report_lib) EXPORT;
+}  // extern "C"
 
-// Set log severity, different levels are:
-// verbose, debug, info, warning, error, fatal.
-bool SetLogSeverity(ReportLib* report_lib, const char* log_level) EXPORT;
-bool SetSymfs(ReportLib* report_lib, const char* symfs_dir) EXPORT;
-bool SetRecordFile(ReportLib* report_lib, const char* record_file) EXPORT;
-bool SetKallsymsFile(ReportLib* report_lib, const char* kallsyms_file) EXPORT;
-void ShowIpForUnknownSymbol(ReportLib* report_lib) EXPORT;
-void ShowArtFrames(ReportLib* report_lib, bool show) EXPORT;
-void MergeJavaMethods(ReportLib* report_lib, bool merge) EXPORT;
-
-Sample* GetNextSample(ReportLib* report_lib) EXPORT;
-Event* GetEventOfCurrentSample(ReportLib* report_lib) EXPORT;
-SymbolEntry* GetSymbolOfCurrentSample(ReportLib* report_lib) EXPORT;
-CallChain* GetCallChainOfCurrentSample(ReportLib* report_lib) EXPORT;
-const char* GetTracingDataOfCurrentSample(ReportLib* report_lib) EXPORT;
-
-const char* GetBuildIdForPath(ReportLib* report_lib, const char* path) EXPORT;
-FeatureSection* GetFeatureSection(ReportLib* report_lib, const char* feature_name) EXPORT;
-}
+namespace simpleperf {
 
 struct EventInfo {
   perf_event_attr attr;
@@ -418,6 +391,39 @@
   return &feature_section_;
 }
 
+}  // namespace simpleperf
+
+using ReportLib = simpleperf::ReportLib;
+
+extern "C" {
+
+#define EXPORT __attribute__((visibility("default")))
+
+// Create a new instance,
+// pass the instance to the other functions below.
+ReportLib* CreateReportLib() EXPORT;
+void DestroyReportLib(ReportLib* report_lib) EXPORT;
+
+// Set log severity, different levels are:
+// verbose, debug, info, warning, error, fatal.
+bool SetLogSeverity(ReportLib* report_lib, const char* log_level) EXPORT;
+bool SetSymfs(ReportLib* report_lib, const char* symfs_dir) EXPORT;
+bool SetRecordFile(ReportLib* report_lib, const char* record_file) EXPORT;
+bool SetKallsymsFile(ReportLib* report_lib, const char* kallsyms_file) EXPORT;
+void ShowIpForUnknownSymbol(ReportLib* report_lib) EXPORT;
+void ShowArtFrames(ReportLib* report_lib, bool show) EXPORT;
+void MergeJavaMethods(ReportLib* report_lib, bool merge) EXPORT;
+
+Sample* GetNextSample(ReportLib* report_lib) EXPORT;
+Event* GetEventOfCurrentSample(ReportLib* report_lib) EXPORT;
+SymbolEntry* GetSymbolOfCurrentSample(ReportLib* report_lib) EXPORT;
+CallChain* GetCallChainOfCurrentSample(ReportLib* report_lib) EXPORT;
+const char* GetTracingDataOfCurrentSample(ReportLib* report_lib) EXPORT;
+
+const char* GetBuildIdForPath(ReportLib* report_lib, const char* path) EXPORT;
+FeatureSection* GetFeatureSection(ReportLib* report_lib, const char* feature_name) EXPORT;
+}
+
 // Exported methods working with a client created instance
 ReportLib* CreateReportLib() {
   return new ReportLib();
diff --git a/simpleperf/sample_tree.h b/simpleperf/sample_tree.h
index 3e5936a..4d5152f 100644
--- a/simpleperf/sample_tree.h
+++ b/simpleperf/sample_tree.h
@@ -27,7 +27,7 @@
 #include "record.h"
 #include "thread_tree.h"
 
-using namespace simpleperf;
+namespace simpleperf {
 
 // A SampleTree is a collection of samples. A profiling report is mainly about
 // constructing a SampleTree and display it. There are three steps involved:
@@ -346,4 +346,6 @@
   SampleDisplayer<EntryT, InfoT> displayer_;
 };
 
+}  // namespace simpleperf
+
 #endif  // SIMPLE_PERF_SAMPLE_TREE_H_
diff --git a/simpleperf/sample_tree_test.cpp b/simpleperf/sample_tree_test.cpp
index 56f4a7e..bee187d 100644
--- a/simpleperf/sample_tree_test.cpp
+++ b/simpleperf/sample_tree_test.cpp
@@ -19,6 +19,8 @@
 #include "sample_tree.h"
 #include "thread_tree.h"
 
+using namespace simpleperf;
+
 namespace {
 
 struct SampleEntry {
diff --git a/simpleperf/test_util.h b/simpleperf/test_util.h
index 8c4a41c..d3d9b46 100644
--- a/simpleperf/test_util.h
+++ b/simpleperf/test_util.h
@@ -24,8 +24,11 @@
 
 #include "environment.h"
 #include "read_elf.h"
+#include "utils.h"
 #include "workload.h"
 
+using namespace simpleperf;
+
 static const std::string SLEEP_SEC = "0.001";
 
 void RunWorkloadFunction();
@@ -34,8 +37,6 @@
 void ParseSymbol(const ElfFileSymbol& symbol, std::map<std::string, ElfFileSymbol>* symbols);
 void CheckElfFileSymbols(const std::map<std::string, ElfFileSymbol>& symbols);
 
-bool IsRoot();
-
 #define TEST_IN_ROOT(TestStatement)                                                            \
   do {                                                                                         \
     if (IsRoot()) {                                                                            \
diff --git a/simpleperf/thread_tree.cpp b/simpleperf/thread_tree.cpp
index b738937..9aad38b 100644
--- a/simpleperf/thread_tree.cpp
+++ b/simpleperf/thread_tree.cpp
@@ -30,7 +30,6 @@
 #include "utils.h"
 
 namespace simpleperf {
-
 namespace {
 
 // Real map file path depends on where the process can create files.
diff --git a/simpleperf/thread_tree.h b/simpleperf/thread_tree.h
index d2a365f..4003fda 100644
--- a/simpleperf/thread_tree.h
+++ b/simpleperf/thread_tree.h
@@ -26,13 +26,13 @@
 
 #include "dso.h"
 
+namespace simpleperf {
+
 struct Record;
 
 constexpr char DEFAULT_KERNEL_MMAP_NAME[] = "[kernel.kallsyms]";
 constexpr char DEFAULT_EXECNAME_FOR_THREAD_MMAP[] = "//anon";
 
-namespace simpleperf {
-
 namespace map_flags {
 constexpr uint32_t PROT_JIT_SYMFILE_MAP = 0x4000;
 }  // namespace map_flags
@@ -170,8 +170,4 @@
 
 }  // namespace simpleperf
 
-using MapEntry = simpleperf::MapEntry;
-using ThreadEntry = simpleperf::ThreadEntry;
-using ThreadTree = simpleperf::ThreadTree;
-
 #endif  // SIMPLE_PERF_THREAD_TREE_H_
diff --git a/simpleperf/tracing.cpp b/simpleperf/tracing.cpp
index 08a6335..cb6a862 100644
--- a/simpleperf/tracing.cpp
+++ b/simpleperf/tracing.cpp
@@ -38,6 +38,8 @@
 using android::base::Split;
 using android::base::StartsWith;
 
+namespace simpleperf {
+
 template <>
 void MoveFromBinaryFormat(std::string& data, const char*& p) {
   data.clear();
@@ -47,8 +49,6 @@
   p++;
 }
 
-namespace simpleperf {
-
 const char TRACING_INFO_MAGIC[10] = {23, 8, 68, 't', 'r', 'a', 'c', 'i', 'n', 'g'};
 
 template <class T>
@@ -147,7 +147,7 @@
   version = "0.5";
   endian = 0;
   size_of_long = static_cast<int>(sizeof(long));  // NOLINT(google-runtime-int)
-  page_size = static_cast<uint32_t>(::GetPageSize());
+  page_size = static_cast<uint32_t>(simpleperf::GetPageSize());
 }
 
 bool TracingFile::RecordHeaderFiles() {
diff --git a/simpleperf/utils.cpp b/simpleperf/utils.cpp
index 387c345..b89f21a 100644
--- a/simpleperf/utils.cpp
+++ b/simpleperf/utils.cpp
@@ -40,6 +40,8 @@
 #include <Xz.h>
 #include <XzCrc64.h>
 
+namespace simpleperf {
+
 using android::base::ParseInt;
 using android::base::Split;
 using android::base::StringPrintf;
@@ -430,3 +432,5 @@
   }
   return tids;
 }
+
+}  // namespace simpleperf
diff --git a/simpleperf/utils.h b/simpleperf/utils.h
index c041f9b..1e3b52b 100644
--- a/simpleperf/utils.h
+++ b/simpleperf/utils.h
@@ -32,6 +32,8 @@
 #include <android-base/unique_fd.h>
 #include <ziparchive/zip_archive.h>
 
+namespace simpleperf {
+
 static inline uint64_t AlignDown(uint64_t value, uint64_t alignment) {
   return value & ~(alignment - 1);
 }
@@ -178,14 +180,12 @@
 std::optional<std::set<int>> GetCpusFromString(const std::string& s);
 std::optional<std::set<pid_t>> GetTidsFromString(const std::string& s, bool check_if_exists);
 
-namespace {
-
 // from boost::hash_combine
 template <typename T>
-void HashCombine(size_t& seed, const T& val) {
+static inline void HashCombine(size_t& seed, const T& val) {
   seed ^= std::hash<T>()(val) + 0x9e3779b9 + (seed << 6) + (seed >> 2);
 }
 
-}  // namespace
+}  // namespace simpleperf
 
 #endif  // SIMPLE_PERF_UTILS_H_
diff --git a/simpleperf/utils_test.cpp b/simpleperf/utils_test.cpp
index 27941a4..7854862 100644
--- a/simpleperf/utils_test.cpp
+++ b/simpleperf/utils_test.cpp
@@ -19,6 +19,8 @@
 #include "get_test_data.h"
 #include "utils.h"
 
+using namespace simpleperf;
+
 TEST(utils, ConvertBytesToValue) {
   char buf[8];
   for (int i = 0; i < 8; ++i) {
diff --git a/simpleperf/workload.cpp b/simpleperf/workload.cpp
index 6fd5510..e82e47b 100644
--- a/simpleperf/workload.cpp
+++ b/simpleperf/workload.cpp
@@ -25,6 +25,8 @@
 #include <android-base/logging.h>
 #include <android-base/strings.h>
 
+namespace simpleperf {
+
 std::unique_ptr<Workload> Workload::CreateWorkload(const std::vector<std::string>& args) {
   std::unique_ptr<Workload> workload(new Workload(args, std::function<void()>()));
   if (workload != nullptr && workload->CreateNewProcess()) {
@@ -202,3 +204,5 @@
   }
   return finished;
 }
+
+}  // namespace simpleperf
diff --git a/simpleperf/workload.h b/simpleperf/workload.h
index cfb5fec..22718a9 100644
--- a/simpleperf/workload.h
+++ b/simpleperf/workload.h
@@ -25,6 +25,8 @@
 
 #include <android-base/macros.h>
 
+namespace simpleperf {
+
 class Workload {
  private:
   enum WorkState {
@@ -71,4 +73,6 @@
   DISALLOW_COPY_AND_ASSIGN(Workload);
 };
 
+}  // namespace simpleperf
+
 #endif  // SIMPLE_PERF_WORKLOAD_H_
diff --git a/simpleperf/workload_test.cpp b/simpleperf/workload_test.cpp
index 33d1c3e..f99ec75 100644
--- a/simpleperf/workload_test.cpp
+++ b/simpleperf/workload_test.cpp
@@ -22,6 +22,8 @@
 #include "utils.h"
 #include "workload.h"
 
+using namespace simpleperf;
+
 TEST(workload, success) {
   IOEventLoop loop;
   ASSERT_TRUE(loop.AddSignalEvent(SIGCHLD, [&]() { return loop.ExitLoop(); }));