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

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

On Tue, Apr 04, 2023 at 02:47:49PM +0200, Andrew Jones wrote:
> On Tue, Apr 04, 2023 at 08:23:15AM +0200, Eric Auger wrote:
> > Hi,
> > 
> > On 3/15/23 12:07, 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-memaccess-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-v1
> > 
> > Gentle ping.
> 
> I'd be happy to take this, but I was hoping to see some r-b's and/or t-b's
> from some of the others.

Any takers? Ricardo? Alexandru?

Thanks,
drew