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

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Date:   Wed, 27 Sep 2023 10:46:17 +0530
From:   Wyes Karny <wyes.karny@....com>
To:     Doug Smythies <dsmythies@...us.net>
Cc:     lenb@...nel.org, linux-pm@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH] tools/power turbostat: Increase the limit for fd opened

Hi Doug,

Thanks for taking a look at the patch.

On 22 Sep 13:48, Doug Smythies wrote:
> 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.

I think below will fix the problem.

+#define MAX_NOFILE 0x8000
+
+void set_rlimit(void)
+{
+       struct rlimit limit;
+
+       if(getrlimit(RLIMIT_NOFILE, &limit) < 0) {
+               err(1, "Failed to get rlimit");
+       }
+
+       if (limit.rlim_max < MAX_NOFILE)
+               limit.rlim_max = MAX_NOFILE;
+       if (limit.rlim_cur < MAX_NOFILE)
+               limit.rlim_cur = MAX_NOFILE;
+
+       if (setrlimit(RLIMIT_NOFILE, &limit) < 0) {
+               err(1, "Failed to set rlimit");
+       }
+       return;
+}


Is this looks okay to you?

Thanks,
Wyes
> 
> 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
> >
>