Re: [kvm-unit-tests PATCH v2 0/6] arm: pmu: Fix random failures of pmu-chain-promotion

[Alexandru Elisei <alexandru.elisei@arm.com>]

Hi,

On Wed, Jun 07, 2023 at 09:07:09PM +0200, Andrew Jones wrote:
> On Wed, May 31, 2023 at 10:14:32PM +0200, Eric Auger wrote:
> > On some HW (ThunderXv2), some random failures of
> > pmu-chain-promotion test can be observed.
> > 
> > pmu-chain-promotion is composed of several subtests
> > which run 2 mem_access loops. The initial value of
> > the counter is set so that no overflow is expected on
> > the first loop run and overflow is expected on the second.
> > However it is observed that sometimes we get an overflow
> > on the first run. It looks related to some variability of
> > the mem_acess count. This variability is observed on all
> > HW I have access to, with different span though. On
> > ThunderX2 HW it looks the margin that is currently taken
> > is too small and we regularly hit failure.
> > 
> > although the first goal of this series is to increase
> > the count/margin used in those tests, it also attempts
> > to improve the pmu-chain-promotion logs, add some barriers
> > in the mem-access loop, clarify the chain counter
> > enable/disable sequence.
> > 
> > A new 'pmu-mem-access-reliability' is also introduced to
> > detect issues with MEM_ACCESS event variability and make
> > the debug easier.
> > 
> > Obviously one can wonder if this variability is something normal
> > and does not hide any other bug. I hope this series will raise
> > additional discussions about this.
> > 
> > https://github.com/eauger/kut/tree/pmu-chain-promotion-fixes-v2
> > 
> > History:
> > v1 -> v2:
> > - Take into account Alexandru's & Mark's comments. Added some
> >   R-b's and T-b's.
> > 
> > Eric Auger (6):
> >   arm: pmu: pmu-chain-promotion: Improve debug messages
> >   arm: pmu: pmu-chain-promotion: Introduce defines for count and margin
> >     values
> >   arm: pmu: Add extra DSB barriers in the mem_access loop
> >   arm: pmu: Fix chain counter enable/disable sequences
> >   arm: pmu: Add pmu-mem-access-reliability test
> >   arm: pmu-chain-promotion: Increase the count and margin values
> > 
> >  arm/pmu.c         | 196 +++++++++++++++++++++++++++++++++-------------
> >  arm/unittests.cfg |   6 ++
> >  2 files changed, 148 insertions(+), 54 deletions(-)
> > 
> > -- 
> > 2.38.1
> >
> 
> Hi Eric,
> 
> I'm eager to merge this, but I'll give Alexandru some time to revisit it
> since he had comments on the last revision.

I've just come back from holiday, I'll have a look next week.

Thanks,
Alex

> 
> Thanks,
> drew