linux-kernel - Re: [PATCH] perf sched replay: Fix -r/--repeat command line option for infinity

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Date: Tue, 18 Jun 2024 14:04:42 +0100
From: James Clark <james.clark@....com>
To: Madadi Vineeth Reddy <vineethr@...ux.ibm.com>,
 Arnaldo Carvalho de Melo <acme@...nel.org>,
 Namhyung Kim <namhyung@...nel.org>, Ian Rogers <irogers@...gle.com>,
 Athira Rajeev <atrajeev@...ux.vnet.ibm.com>, Chen Yu <yu.c.chen@...el.com>
Cc: Peter Zijlstra <peterz@...radead.org>, Ingo Molnar <mingo@...hat.com>,
 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>, acme@...hat.com,
 Fernand Sieber <sieberf@...zon.com>,
 linux-perf-users <linux-perf-users@...r.kernel.org>,
 LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] perf sched replay: Fix -r/--repeat command line option
 for infinity



On 18/06/2024 12:29, Madadi Vineeth Reddy wrote:
> Currently, the -r/--repeat option accepts values from 0 and complains
> for -1. The help section specifies:
> -r, --repeat <n>      repeat the workload replay N times (-1: infinite)
> 

I was wondering if this was a regression or was always like this but
it's at least been broken long before it becomes difficult to build
Perf for me.

> The -r -1 option raises an error because replay_repeat is defined as
> an unsigned int.
> 
> In the current implementation, the workload is repeated n times when
> -r <n> is used, except when n is 0.
> 
> When -r is set to 0, the workload is also repeated once. This happens
> because when -r=0, the run_one_test function is not called. (Note that
> mutex unlocking, which is essential for child threads spawned to emulate
> the workload, happens in run_one_test.) However, mutex unlocking is
> still performed in the destroy_tasks function. Thus, -r=0 results in the
> workload running once coincidentally.
> 

I also saw an intermittent hang waiting in destroy_tasks() which is now
fixed.
 
> To clarify and maintain the existing logic for -r >= 1 (which runs the
> workload the specified number of times) and to fix the issue with infinite
> runs, make -r=0 perform an infinite run.
> 
> Signed-off-by: Madadi Vineeth Reddy <vineethr@...ux.ibm.com>
> ---
>  tools/perf/Documentation/perf-sched.txt | 7 +++++++
>  tools/perf/builtin-sched.c              | 8 ++++++--
>  2 files changed, 13 insertions(+), 2 deletions(-)
> 
> diff --git a/tools/perf/Documentation/perf-sched.txt b/tools/perf/Documentation/perf-sched.txt
> index a216d2991b19..f1be8f0b249e 100644
> --- a/tools/perf/Documentation/perf-sched.txt
> +++ b/tools/perf/Documentation/perf-sched.txt
> @@ -202,6 +202,13 @@ OPTIONS for 'perf sched timehist'
>  --state::
>  	Show task state when it switched out.
>  
> +OPTIONS for 'perf sched replay'
> +------------------------------
> +
> +-r::
> +--repeat <n>::
> +	repeat the workload n times (0: infinite). Default is 10.
> +
>  SEE ALSO
>  --------
>  linkperf:perf-record[1]
> diff --git a/tools/perf/builtin-sched.c b/tools/perf/builtin-sched.c
> index 8cdf18139a7e..2c4ed5c2d695 100644
> --- a/tools/perf/builtin-sched.c
> +++ b/tools/perf/builtin-sched.c
> @@ -3383,8 +3383,12 @@ static int perf_sched__replay(struct perf_sched *sched)
>  	sched->thread_funcs_exit = false;
>  	create_tasks(sched);
>  	printf("------------------------------------------------------------\n");
> -	for (i = 0; i < sched->replay_repeat; i++)
> +
> +	i = 0;
> +	while (sched->replay_repeat == 0 || i < sched->replay_repeat) {

Very minor nit, but you don't really need to remove the for loop, just add
the new condition to the existing one. Not sure if it's worth re-spinning
for though.

Reviewed-by: James Clark <james.clark@....com>

>  		run_one_test(sched);
> +		i++;
> +	}
>  
>  	sched->thread_funcs_exit = true;
>  	destroy_tasks(sched);
> @@ -3548,7 +3552,7 @@ int cmd_sched(int argc, const char **argv)
>  	};
>  	const struct option replay_options[] = {
>  	OPT_UINTEGER('r', "repeat", &sched.replay_repeat,
> -		     "repeat the workload replay N times (-1: infinite)"),
> +		     "repeat the workload replay N times (0: infinite)"),
>  	OPT_PARENT(sched_options)
>  	};
>  	const struct option map_options[] = {