linux-kernel - Re: [PATCH] perf/bench: Fix perf bench syscall XXXX loop count

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Message-Id: <69345A2D-EF10-4530-8C95-1E7BDC0B64F1@linux.ibm.com>
Date: Tue, 4 Mar 2025 19:44:39 +0530
From: Athira Rajeev <atrajeev@...ux.ibm.com>
To: Thomas Richter <tmricht@...ux.ibm.com>
Cc: LKML <linux-kernel@...r.kernel.org>, linux-s390@...r.kernel.org,
        "open list:PERFORMANCE EVENTS SUBSYSTEM" <linux-perf-users@...r.kernel.org>,
        Arnaldo Carvalho de Melo <acme@...nel.org>,
        Namhyung Kim <namhyung@...nel.org>, yangtiezhu@...ngson.cn,
        agordeev@...ux.ibm.com, gor@...ux.ibm.com, sumanthk@...ux.ibm.com,
        hca@...ux.ibm.com
Subject: Re: [PATCH] perf/bench: Fix perf bench syscall XXXX loop count



> On 4 Mar 2025, at 2:53 PM, Thomas Richter <tmricht@...ux.ibm.com> wrote:
> 
> Command 'perf bench syscall fork -l 100000' offers option
> -l to run for a specified number of iterations. However this
> option is not always observed. The number is silently limited to
> 10000 iterations as can be seen:
> 
> Output before:
> # perf bench syscall fork -l 100000
> # Running 'syscall/fork' benchmark:
> # Executed 10,000 fork() calls
>     Total time: 23.388 [sec]
> 
>    2338.809800 usecs/op
>            427 ops/sec
> #
> 
> When explicitly specified with option -l or --loops, also observe
> higher number of iterations:
> 
> Output after:
> # perf bench syscall fork -l 100000
> # Running 'syscall/fork' benchmark:
> # Executed 100,000 fork() calls
>     Total time: 716.982 [sec]
> 
>    7169.829510 usecs/op
>            139 ops/sec
> #
> 

Tested-by: Athira Rajeev <atrajeev@...ux.ibm.com>

Thanks
Athira
> This patch fixes the issue for basic execve fork and getpgid.
> 
> Fixes: ece7f7c0507c ("perf bench syscall: Add fork syscall benchmark")
> Signed-off-by: Thomas Richter <tmricht@...ux.ibm.com>
> Acked-by: Sumanth Korikkar <sumanthk@...ux.ibm.com>
> Cc: Tiezhu Yang <yangtiezhu@...ngson.cn>
> ---
> tools/perf/bench/syscall.c | 22 +++++++++++++---------
> 1 file changed, 13 insertions(+), 9 deletions(-)
> 
> diff --git a/tools/perf/bench/syscall.c b/tools/perf/bench/syscall.c
> index ea4dfc07cbd6..e7dc216f717f 100644
> --- a/tools/perf/bench/syscall.c
> +++ b/tools/perf/bench/syscall.c
> @@ -22,8 +22,7 @@
> #define __NR_fork -1
> #endif
> 
> -#define LOOPS_DEFAULT 10000000
> -static int loops = LOOPS_DEFAULT;
> +static int loops;
> 
> static const struct option options[] = {
> OPT_INTEGER('l', "loop", &loops, "Specify number of loops"),
> @@ -80,6 +79,18 @@ static int bench_syscall_common(int argc, const char **argv, int syscall)
> const char *name = NULL;
> int i;
> 
> + switch (syscall) {
> + case __NR_fork:
> + case __NR_execve:
> + /* Limit default loop to 10000 times to save time */
> + loops = 10000;
> + break;
> + default:
> + loops = 10000000;
> + break;
> + }
> +
> + /* Options -l and --loops override default above */
> argc = parse_options(argc, argv, options, bench_syscall_usage, 0);
> 
> gettimeofday(&start, NULL);
> @@ -94,16 +105,9 @@ static int bench_syscall_common(int argc, const char **argv, int syscall)
> break;
> case __NR_fork:
> test_fork();
> - /* Only loop 10000 times to save time */
> - if (i == 10000)
> - loops = 10000;
> break;
> case __NR_execve:
> test_execve();
> - /* Only loop 10000 times to save time */
> - if (i == 10000)
> - loops = 10000;
> - break;
> default:
> break;
> }
> -- 
> 2.47.0
> 
>