Re: [PATCH] perf data: Increase RLIMIT_NOFILE limit when open too many files in perf_data__create_dir()

[Yang Jihong]

Hello,

On 2023/10/20 13:59, Namhyung Kim wrote:
> Hello,
>
> On Fri, Oct 13, 2023 at 1:01 AM Yang Jihong <yangjihong1@xxxxxxxxxx> wrote:
> > If using parallel threads to collect data, perf record needs at least 6 fds
> > per CPU. (one for sys_perf_event_open, four for pipe msg and ack of the
> > pipe, see record__thread_data_open_pipes(), and one for open perf.data.XXX)
>
> Yep, probably one more for the dummy event.
>
> > For an environment with more than 100 cores, if perf record uses both
> > `-a` and `--threads` options, it is easy to exceed the upper limit of the
> > file descriptor number, when we run out of them try to increase the limits.
> >
> > Before:
> >    $ ulimit -n
> >    1024
> >    $ lscpu | grep 'On-line CPU(s)'
> >    On-line CPU(s) list:                0-159
> >    $ perf record --threads -a sleep 1
> >    Failed to create data directory: Too many open files
> >
> > After:
> >    $ ulimit -n
> >    1024
> >    $ lscpu | grep 'On-line CPU(s)'
> >    On-line CPU(s) list:                0-159
> >    $ perf record --threads -a sleep 1
> >    [ perf record: Woken up 1 times to write data ]
> >    [ perf record: Captured and wrote 0.394 MB perf.data (1576 samples) ]
> > Signed-off-by: Yang Jihong <yangjihong1@xxxxxxxxxx>
> > ---
> >   tools/perf/util/data.c | 12 ++++++++++++
> >   1 file changed, 12 insertions(+)
> >
> > diff --git a/tools/perf/util/data.c b/tools/perf/util/data.c
> > index fc16299c915f..098f9e3bb2e7 100644
> > --- a/tools/perf/util/data.c
> > +++ b/tools/perf/util/data.c
> > @@ -17,6 +17,7 @@
> >   #include "util.h" // rm_rf_perf_data()
> >   #include "debug.h"
> >   #include "header.h"
> > +#include "evsel.h"
> >   #include <internal/lib.h>
> >
> >   static void close_dir(struct perf_data_file *files, int nr)
> > @@ -35,6 +36,7 @@ void perf_data__close_dir(struct perf_data *data)
> >
> >   int perf_data__create_dir(struct perf_data *data, int nr)
> >   {
> > +       enum rlimit_action set_rlimit = NO_CHANGE;
> >          struct perf_data_file *files = NULL;
> >          int i, ret;
> >
> > @@ -54,11 +56,21 @@ int perf_data__create_dir(struct perf_data *data, int nr)
> >                          goto out_err;
> >                  }
> >
> > +retry_open:
> >                  ret = open(file->path, O_RDWR|O_CREAT|O_TRUNC, S_IRUSR|S_IWUSR);
> >                  if (ret < 0) {
> > +                       /*
> > +                        * If using parallel threads to collect data,
> > +                        * perf record needs at least 6 fds per CPU.
> > +                        * When we run out of them try to increase the limits.
> > +                        */
> > +                       if (errno == EMFILE && evsel__increase_rlimit(&set_rlimit))
>
> It seems weird that we have this helper with evsel prefix and
> it does nothing with evsel.  But it's a separate concern, so
>
> Acked-by: Namhyung Kim <namhyung@xxxxxxxxxx>
Thanks for the Acked-by tag.

Uh... The name of this helper doesn't seem to be appropriate.
Okay, I'll submit a patch to fix this helper name.

Thanks,
Yang