linux-kernel - Re: [PATCH] perf/amd: Prevent grouping of IBS events

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Message-ID: <3b0abd4a-6450-c282-65ff-ec0c7df67b03@amd.com>
Date:   Wed, 21 Jun 2023 08:57:41 +0530
From:   Ravi Bangoria <ravi.bangoria@....com>
To:     Ian Rogers <irogers@...gle.com>
Cc:     peterz@...radead.org, acme@...nel.org, jolsa@...nel.org,
        namhyung@...nel.org, bp@...en8.de, x86@...nel.org,
        linux-perf-users@...r.kernel.org, linux-kernel@...r.kernel.org,
        sandipan.das@....com, ananth.narayan@....com,
        santosh.shukla@....com, Ravi Bangoria <ravi.bangoria@....com>
Subject: Re: [PATCH] perf/amd: Prevent grouping of IBS events

Hi Ian,

On 20-Jun-23 10:14 PM, Ian Rogers wrote:
> On Tue, Jun 20, 2023 at 2:16 AM Ravi Bangoria <ravi.bangoria@....com> wrote:
>>
>> IBS PMUs can have only one event active at any point in time. Restrict
>> grouping of multiple IBS events.
> 
> Thanks Ravi,
> 
> can you provide an example/test for this? Should this be a weak group issue?

Before:
  $ sudo ./perf record -e "{ibs_op//,ibs_op//}" -C 0
  ^C[ perf record: Woken up 1 times to write data ]
  [ perf record: Captured and wrote 0.540 MB perf.data (531 samples) ]

After:
  $ sudo ./perf record -e "{ibs_op//,ibs_op//}" -C 0
  Error:
  AMD IBS may only be available in system-wide/per-cpu mode.
  Try using -a, or -C and workload affinity

The error message is stale and misleading. I have a patch to fix it.
I'll post it separately.

Thanks,
Ravi