tree 0fbf4c1455c00af8734c4889c28327120ab69f52
parent bdbe8cc1a30c7280bc5e6119fb5d37bfdd723c47
author Fred Lotter <frederik.lotter@netronome.com> 1547608011 -0800
committer David S. Miller <davem@davemloft.net> 1547680994 -0800

nfp: flower: increase cmesg reply timeout

QA tests report occasional timeouts on REIFY message replies. Profiling
of the two cmesg reply types under burst conditions, with a 12-core host
under heavy cpu and io load (stress --cpu 12 --io 12), show both PHY MTU
change and REIFY replies can exceed the 10ms timeout. The maximum MTU
reply wait under burst is 16ms, while the maximum REIFY wait under 40 VF
burst is 12ms. Using a 4 VF REIFY burst results in an 8ms maximum wait.
A larger VF burst does increase the delay, but not in a linear enough
way to justify a scaled REIFY delay. The worse case values between
MTU and REIFY appears close enough to justify a common timeout. Pick a
conservative 40ms to make a safer future proof common reply timeout. The
delay only effects the failure case.

Change the REIFY timeout mechanism to use wait_event_timeout() instead
of wait_event_interruptible_timeout(), to match the MTU code. In the
current implementation, theoretically, a signal could interrupt the
REIFY waiting period, with a return code of ERESTARTSYS. However, this is
caught under the general timeout error code EIO. I cannot see the benefit
of exposing the REIFY waiting period to signals with such a short delay
(40ms), while the MTU mechnism does not use the same logic. In the absence
of any reply (wakeup() call), both reply types will wake up the task after
the timeout period. The REIFY timeout applies to the entire representor
group being instantiated (e.g. VFs), while the MTU timeout apples to a
single PHY MTU change.

Signed-off-by: Fred Lotter <frederik.lotter@netronome.com>
Reviewed-by: Jakub Kicinski <jakub.kicinski@netronome.com>
Signed-off-by: David S. Miller <davem@davemloft.net>