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

[Andrew Jones <andrew.jones@linux.dev>]

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.

Thanks,
drew