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

[Namhyung Kim]

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,
Namhyung


> +                               goto retry_open;
> +
>                         ret = -errno;
>                         goto out_err;
>                 }
> +               set_rlimit = NO_CHANGE;
>
>                 file->fd = ret;
>         }
> --
> 2.34.1
>