linux-kernel - Re: [PATCH v2 07/18] perf record: Update use of pthread mutex

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Message-ID: <02152f40-1dc5-7f1b-ad88-61ecb146a3da@intel.com>
Date:   Wed, 24 Aug 2022 13:14:55 +0300
From:   Adrian Hunter <adrian.hunter@...el.com>
To:     Ian Rogers <irogers@...gle.com>,
        Peter Zijlstra <peterz@...radead.org>,
        Ingo Molnar <mingo@...hat.com>,
        Arnaldo Carvalho de Melo <acme@...nel.org>,
        Mark Rutland <mark.rutland@....com>,
        Alexander Shishkin <alexander.shishkin@...ux.intel.com>,
        Jiri Olsa <jolsa@...nel.org>,
        Namhyung Kim <namhyung@...nel.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Darren Hart <dvhart@...radead.org>,
        Davidlohr Bueso <dave@...olabs.net>,
        André Almeida <andrealmeid@...lia.com>,
        Nathan Chancellor <nathan@...nel.org>,
        Nick Desaulniers <ndesaulniers@...gle.com>,
        Tom Rix <trix@...hat.com>, Weiguo Li <liwg06@...mail.com>,
        Athira Rajeev <atrajeev@...ux.vnet.ibm.com>,
        Thomas Richter <tmricht@...ux.ibm.com>,
        Ravi Bangoria <ravi.bangoria@....com>,
        Dario Petrillo <dario.pk1@...il.com>,
        Hewenliang <hewenliang4@...wei.com>,
        yaowenbin <yaowenbin1@...wei.com>,
        Wenyu Liu <liuwenyu7@...wei.com>,
        Song Liu <songliubraving@...com>,
        Andrii Nakryiko <andrii@...nel.org>,
        Dave Marchevsky <davemarchevsky@...com>,
        Leo Yan <leo.yan@...aro.org>,
        Kim Phillips <kim.phillips@....com>,
        Pavithra Gurushankar <gpavithrasha@...il.com>,
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        Quentin Monnet <quentin@...valent.com>,
        William Cohen <wcohen@...hat.com>,
        Andres Freund <andres@...razel.de>,
        Adrian Hunter <adrian.hunter@...el.com>,
        Martin Liška <mliska@...e.cz>,
        Colin Ian King <colin.king@...el.com>,
        James Clark <james.clark@....com>,
        Fangrui Song <maskray@...gle.com>,
        Stephane Eranian <eranian@...gle.com>,
        Kajol Jain <kjain@...ux.ibm.com>,
        Alexey Bayduraev <alexey.v.bayduraev@...ux.intel.com>,
        Riccardo Mancini <rickyman7@...il.com>,
        Andi Kleen <ak@...ux.intel.com>,
        Masami Hiramatsu <mhiramat@...nel.org>,
        Zechuan Chen <chenzechuan1@...wei.com>,
        Jason Wang <wangborong@...rlc.com>,
        Christophe JAILLET <christophe.jaillet@...adoo.fr>,
        Remi Bernon <rbernon@...eweavers.com>,
        linux-kernel@...r.kernel.org, linux-perf-users@...r.kernel.org,
        bpf@...r.kernel.org, llvm@...ts.linux.dev
Subject: Re: [PATCH v2 07/18] perf record: Update use of pthread mutex

On 24/08/22 01:09, Ian Rogers wrote:
> Switch to the use of mutex wrappers that provide better error checking
> for synth_lock.

It would be better to distinguish patches that make drop-in
replacements from patches like this that change logic.

> 
> Signed-off-by: Ian Rogers <irogers@...gle.com>
> ---
>  tools/perf/builtin-record.c | 13 +++++++++----
>  1 file changed, 9 insertions(+), 4 deletions(-)
> 
> diff --git a/tools/perf/builtin-record.c b/tools/perf/builtin-record.c
> index 4713f0f3a6cf..02eb85677e99 100644
> --- a/tools/perf/builtin-record.c
> +++ b/tools/perf/builtin-record.c
> @@ -21,6 +21,7 @@
>  #include "util/evsel.h"
>  #include "util/debug.h"
>  #include "util/mmap.h"
> +#include "util/mutex.h"
>  #include "util/target.h"
>  #include "util/session.h"
>  #include "util/tool.h"
> @@ -608,17 +609,18 @@ static int process_synthesized_event(struct perf_tool *tool,
>  	return record__write(rec, NULL, event, event->header.size);
>  }
>  
> +static struct mutex synth_lock;
> +
>  static int process_locked_synthesized_event(struct perf_tool *tool,
>  				     union perf_event *event,
>  				     struct perf_sample *sample __maybe_unused,
>  				     struct machine *machine __maybe_unused)
>  {
> -	static pthread_mutex_t synth_lock = PTHREAD_MUTEX_INITIALIZER;
>  	int ret;
>  
> -	pthread_mutex_lock(&synth_lock);
> +	mutex_lock(&synth_lock);
>  	ret = process_synthesized_event(tool, event, sample, machine);
> -	pthread_mutex_unlock(&synth_lock);
> +	mutex_unlock(&synth_lock);
>  	return ret;
>  }
>  
> @@ -1917,6 +1919,7 @@ static int record__synthesize(struct record *rec, bool tail)
>  	}
>  
>  	if (rec->opts.nr_threads_synthesize > 1) {
> +		mutex_init(&synth_lock, /*pshared=*/false);

It would be better to have mutex_init() and mutex_init_shared()
since /*pshared=*/true is rarely used.

>  		perf_set_multithreaded();
>  		f = process_locked_synthesized_event;
>  	}
> @@ -1930,8 +1933,10 @@ static int record__synthesize(struct record *rec, bool tail)
>  						    rec->opts.nr_threads_synthesize);
>  	}
>  
> -	if (rec->opts.nr_threads_synthesize > 1)
> +	if (rec->opts.nr_threads_synthesize > 1) {
>  		perf_set_singlethreaded();
> +		mutex_destroy(&synth_lock);
> +	}
>  
>  out:
>  	return err;