linux-kernel - Re: [PATCH v1] perf cpumap: Increment reference count for online cpumap

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Message-ID: <a27a9066-b0e3-4d8f-bbb3-2dfd080800ef@linux.ibm.com>
Date: Wed, 19 Mar 2025 10:05:05 +0100
From: Thomas Richter <tmricht@...ux.ibm.com>
To: Ian Rogers <irogers@...gle.com>,
        Suzuki K Poulose
 <suzuki.poulose@....com>,
        Mike Leach <mike.leach@...aro.org>,
        James Clark <james.clark@...aro.org>,
        John Garry <john.g.garry@...cle.com>, Will Deacon <will@...nel.org>,
        Leo Yan <leo.yan@...ux.dev>, Peter Zijlstra <peterz@...radead.org>,
        Ingo Molnar <mingo@...hat.com>,
        Arnaldo Carvalho de Melo <acme@...nel.org>,
        Namhyung Kim <namhyung@...nel.org>,
        Mark Rutland <mark.rutland@....com>,
        Alexander Shishkin <alexander.shishkin@...ux.intel.com>,
        Jiri Olsa <jolsa@...nel.org>, Adrian Hunter <adrian.hunter@...el.com>,
        Kan Liang <kan.liang@...ux.intel.com>,
        Howard Chu <howardchu95@...il.com>, Levi Yun <yeoreum.yun@....com>,
        "Dr. David Alan Gilbert"
 <linux@...blig.org>,
        Thomas Falcon <thomas.falcon@...el.com>, coresight@...ts.linaro.org,
        linux-arm-kernel@...ts.infradead.org, linux-perf-users@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH v1] perf cpumap: Increment reference count for online
 cpumap

On 3/18/25 18:19, Ian Rogers wrote:
> Thomas Richter <tmricht@...ux.ibm.com> reported a double put on the
> cpumap for the placeholder core PMU:
> https://lore.kernel.org/lkml/20250318095132.1502654-3-tmricht@linux.ibm.com/
> Requiring the caller to get the cpumap is not how these things are
> usually done, switch cpu_map__online to do the get and then fix up any
> use cases where a put is needed.
> 
> Signed-off-by: Ian Rogers <irogers@...gle.com>

Ian,

thanks for fixing this. Here are the results on s390 z/VM:

# ./perf bench internals pmu-scan
# Running 'internals/pmu-scan' benchmark:
Computing performance of sysfs PMU event scan for 100 times
  Average core PMU scanning took: 6.340 usec (+- 0.050 usec)
  Average PMU scanning took: 93.785 usec (+- 6.210 usec)
# 

Tested-by: Thomas Richter <tmricht@...ux.ibm.com>

-- 
Thomas Richter, Dept 3303, IBM s390 Linux Development, Boeblingen, Germany
--
IBM Deutschland Research & Development GmbH

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