ART: Optimize PreSetup pass for oat-file open
The PreSetup pass for opening an oatfile with dlopen parses all
shared objects and tries to retrieve the corresponding mem map
(so as to have a fake MemMap to reserve the space for any scanning
operations and so on). Optimistically optimize this pass by counting
the number of shared objects before the dlopen, and skipping as
many afterwards.
This saves about half a millisecond on an N6P.
Bug: 28801010
Change-Id: I70156f9875e89c5af3c9e36e8f01c5662e3f736e
diff --git a/runtime/oat_file.cc b/runtime/oat_file.cc
index ccb8b29..429cba8 100644
--- a/runtime/oat_file.cc
+++ b/runtime/oat_file.cc
@@ -98,6 +98,8 @@
virtual const uint8_t* FindDynamicSymbolAddress(const std::string& symbol_name,
std::string* error_msg) const = 0;
+ virtual void PreLoad() = 0;
+
virtual bool Load(const std::string& elf_filename,
uint8_t* oat_file_begin,
bool writable,
@@ -138,6 +140,9 @@
const char* abs_dex_location,
std::string* error_msg) {
std::unique_ptr<OatFileBase> ret(new kOatFileBaseSubType(location, executable));
+
+ ret->PreLoad();
+
if (!ret->Load(elf_filename,
oat_file_begin,
writable,
@@ -150,6 +155,7 @@
if (!ret->ComputeFields(requested_base, elf_filename, error_msg)) {
return nullptr;
}
+
ret->PreSetup(elf_filename);
if (!ret->Setup(abs_dex_location, error_msg)) {
@@ -509,6 +515,7 @@
DlOpenOatFile(const std::string& filename, bool executable)
: OatFileBase(filename, executable),
dlopen_handle_(nullptr),
+ shared_objects_before_(0),
first_oat_(RegisterOatFileLocation(filename)) {
}
@@ -530,6 +537,8 @@
return ptr;
}
+ void PreLoad() OVERRIDE;
+
bool Load(const std::string& elf_filename,
uint8_t* oat_file_begin,
bool writable,
@@ -551,12 +560,37 @@
// Dummy memory map objects corresponding to the regions mapped by dlopen.
std::vector<std::unique_ptr<MemMap>> dlopen_mmaps_;
+ // The number of shared objects the linker told us about before loading. Used to
+ // (optimistically) optimize the PreSetup stage (see comment there).
+ size_t shared_objects_before_;
+
// Track the registration status (= was this the first oat file) for the location.
const bool first_oat_;
DISALLOW_COPY_AND_ASSIGN(DlOpenOatFile);
};
+void DlOpenOatFile::PreLoad() {
+#ifdef __APPLE__
+ LOG(FATAL) << "Should not reach here.";
+ UNREACHABLE();
+#else
+ // Count the entries in dl_iterate_phdr we get at this point in time.
+ struct dl_iterate_context {
+ static int callback(struct dl_phdr_info *info ATTRIBUTE_UNUSED,
+ size_t size ATTRIBUTE_UNUSED,
+ void *data) {
+ reinterpret_cast<dl_iterate_context*>(data)->count++;
+ return 0; // Continue iteration.
+ }
+ size_t count = 0;
+ } context;
+
+ dl_iterate_phdr(dl_iterate_context::callback, &context);
+ shared_objects_before_ = context.count;
+#endif
+}
+
bool DlOpenOatFile::Load(const std::string& elf_filename,
uint8_t* oat_file_begin,
bool writable,
@@ -657,6 +691,14 @@
struct dl_iterate_context {
static int callback(struct dl_phdr_info *info, size_t /* size */, void *data) {
auto* context = reinterpret_cast<dl_iterate_context*>(data);
+ context->shared_objects_seen++;
+ if (context->shared_objects_seen < context->shared_objects_before) {
+ // We haven't been called yet for anything we haven't seen before. Just continue.
+ // Note: this is aggressively optimistic. If another thread was unloading a library,
+ // we may miss out here. However, this does not happen often in practice.
+ return 0;
+ }
+
// See whether this callback corresponds to the file which we have just loaded.
bool contains_begin = false;
for (int i = 0; i < info->dlpi_phnum; i++) {
@@ -687,11 +729,22 @@
}
const uint8_t* const begin_;
std::vector<std::unique_ptr<MemMap>>* const dlopen_mmaps_;
- } context = { Begin(), &dlopen_mmaps_ };
+ const size_t shared_objects_before;
+ size_t shared_objects_seen;
+ };
+ dl_iterate_context context = { Begin(), &dlopen_mmaps_, shared_objects_before_, 0};
if (dl_iterate_phdr(dl_iterate_context::callback, &context) == 0) {
- PrintFileToLog("/proc/self/maps", LogSeverity::WARNING);
- LOG(ERROR) << "File " << elf_filename << " loaded with dlopen but cannot find its mmaps.";
+ // Hm. Maybe our optimization went wrong. Try another time with shared_objects_before == 0
+ // before giving up. This should be unusual.
+ VLOG(oat) << "Need a second run in PreSetup, didn't find with shared_objects_before="
+ << shared_objects_before_;
+ dl_iterate_context context0 = { Begin(), &dlopen_mmaps_, 0, 0};
+ if (dl_iterate_phdr(dl_iterate_context::callback, &context0) == 0) {
+ // OK, give up and print an error.
+ PrintFileToLog("/proc/self/maps", LogSeverity::WARNING);
+ LOG(ERROR) << "File " << elf_filename << " loaded with dlopen but cannot find its mmaps.";
+ }
}
#endif
}
@@ -728,6 +781,9 @@
return ptr;
}
+ void PreLoad() OVERRIDE {
+ }
+
bool Load(const std::string& elf_filename,
uint8_t* oat_file_begin, // Override where the file is loaded to if not null
bool writable,
