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

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Date:   Fri, 23 Aug 2019 18:26:34 +0530
From:   Ganapatrao Kulkarni <gklkml16@...il.com>
To:     Peter Zijlstra <peterz@...radead.org>
Cc:     Ian Rogers <irogers@...gle.com>, Ingo Molnar <mingo@...hat.com>,
        Arnaldo Carvalho de Melo <acme@...nel.org>,
        Alexander Shishkin <alexander.shishkin@...ux.intel.com>,
        Jiri Olsa <jolsa@...hat.com>,
        Namhyung Kim <namhyung@...nel.org>,
        LKML <linux-kernel@...r.kernel.org>,
        Kan Liang <kan.liang@...ux.intel.com>,
        Andi Kleen <ak@...ux.intel.com>,
        Stephane Eranian <eranian@...gle.com>,
        Ganapatrao Kulkarni <gkulkarni@...vell.com>,
        Jayachandran Chandrasekharan Nair <jnair@...vell.com>
Subject: Re: [PATCH] perf cgroups: Don't rotate events for cgroups unnecessarily

Hi Peter,

On Fri, Aug 23, 2019 at 5:29 PM Peter Zijlstra <peterz@...radead.org> 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