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

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Date:   Fri, 23 Aug 2019 13:59:46 +0200
From:   Peter Zijlstra <peterz@...radead.org>
To:     Ganapatrao Kulkarni <gklkml16@...il.com>
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


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?

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.

> 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.