Re: [PATCH] perf cgroups: Don't rotate events for cgroups unnecessarily

From: Ganapatrao Kulkarni
Date: Fri Aug 23 2019 - 08:56:50 EST


Hi Peter,

On Fri, Aug 23, 2019 at 5:29 PM Peter Zijlstra <peterz@xxxxxxxxxxxxx> wrote:
>
>
> A: Because it messes up the order in which people normally read text.
> Q: Why is top-posting such a bad thing?
> A: Top-posting.
> Q: What is the most annoying thing in e-mail?

Sorry for the top-posting.
>
> On Fri, Aug 23, 2019 at 04:13:46PM +0530, Ganapatrao Kulkarni wrote:
>
> > We are seeing regression with our uncore perf driver(Marvell's
> > ThunderX2, ARM64 server platform) on 5.3-Rc1.
> > After bisecting, it turned out to be this patch causing the issue.
>
> Funnily enough; the email you replied to didn't contain a patch.

Hmm sorry, not sure why the patch is clipped-off, I see it in my inbox.
>
> > Test case:
> > Load module and run perf for more than 4 events( we have 4 counters,
> > event multiplexing takes place for more than 4 events), then unload
> > module.
> > With this sequence of testing, the system hangs(soft lockup) after 2
> > or 3 iterations. Same test runs for hours on 5.2.
> >
> > while [ 1 ]
> > do
> > rmmod thunderx2_pmu
> > modprobe thunderx2_pmu
> > perf stat -a -e \
> > uncore_dmc_0/cnt_cycles/,\
> > uncore_dmc_0/data_transfers/,\
> > uncore_dmc_0/read_txns/,\
> > uncore_dmc_0/config=0xE/,\
> > uncore_dmc_0/write_txns/ sleep 1
> > sleep 2
> > done
>
> Can you reproduce without the module load+unload? I don't think people
> routinely unload modules.

The issue wont happen, if module is not unloaded/reloaded.
IMHO, this could be potential bug!

>
>

Thanks,
Ganapat