linux-kernel - RE: [PATCH] tools/power turbostat: Increase the limit for fd opened

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Date:   Fri, 22 Sep 2023 13:48:05 -0700
From:   "Doug Smythies" <dsmythies@...us.net>
To:     "'Wyes Karny'" <wyes.karny@....com>, <lenb@...nel.org>
Cc:     <linux-pm@...r.kernel.org>, <linux-kernel@...r.kernel.org>,
        "Doug Smythies" <dsmythies@...us.net>
Subject: RE: [PATCH] tools/power turbostat: Increase the limit for fd opened

On 2023.09.22 02:28 Wyes Karny wrote:

> When running turbostat, a system with 512 cpus reaches the limit for

Suggest" ... reaches the default limit for..."

> maximum number of file descriptors that can be opened. To solve this
> problem, the limit is raised to 2^15, which is a large enough number.
>
> Below data is collected from AMD server systems while running turbostat:
>
> |-----------+-------------------------------|
> | # of cpus | # of opened fds for turbostat |
> |-----------+-------------------------------|
> | 128       | 260                           |
> |-----------+-------------------------------|
> | 192       | 388                           |
> |-----------+-------------------------------|
> | 512       | 1028                          |
> |-----------+-------------------------------|

The number of open files is a function of what is being "show"ed or "hide"en.
They can also increase beyond the above 2 X (# of CPUs) + 4 number
via the --add directive. 
>
> So, the new max limit would be sufficient up to 2^14 cpus.

Well, not quiet, but the point is valid.

Normally, I would assume that a server with a large number of
CPUs would have set a much higher limit of the number of open
files than the default. I use 131,072 and so this patch reduces the
maximum.

Unpatched:
root@s19:~# cat /proc/47043/limits | grep "Max open files"
Max open files            131072               131072               files

Patched:
root@s19:~# cat /proc/47032/limits | grep "Max open files"
Max open files            32768                32768                files

Anyway:

Reviewed-by: Doug Smythies <dsmythies@...us.net>
Tested-by: Doug Smythies <dsmythies@...us.net>

>
> Signed-off-by: Wyes Karny <wyes.karny@....com>
> ---
>  tools/power/x86/turbostat/turbostat.c | 15 +++++++++++++++
>  1 file changed, 15 insertions(+)
>
> diff --git a/tools/power/x86/turbostat/turbostat.c b/tools/power/x86/turbostat/turbostat.c
> index 9a10512e3407..23f1fe58289a 100644
> --- a/tools/power/x86/turbostat/turbostat.c
> +++ b/tools/power/x86/turbostat/turbostat.c
> @@ -6717,6 +6717,18 @@ void cmdline(int argc, char **argv)
>       }
>  }
>
> +void set_rlimit(void)
> +{
> +     struct rlimit limit;
> +
> +     limit.rlim_cur = 0x8000;
> +     limit.rlim_max = 0x8000;
> +
> +     if (setrlimit(RLIMIT_NOFILE, &limit) < 0) {
> +             err(1, "Failed to set rlimit");
> +     }
> +}
> +
>  int main(int argc, char **argv)
>  {
>       outf = stderr;
> @@ -6729,6 +6741,9 @@ int main(int argc, char **argv)
>
>       probe_sysfs();
>
> +     if (!getuid())
> +             set_rlimit();
> +
>       turbostat_init();
>
>       msr_sum_record();
> --
> 2.34.1
>