linux-kernel - Re: [PATCH 2/5] perf record: Fix done

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Date:   Wed, 24 Aug 2022 08:41:27 -0700
From:   Ian Rogers <irogers@...gle.com>
To:     Adrian Hunter <adrian.hunter@...el.com>
Cc:     Arnaldo Carvalho de Melo <acme@...nel.org>,
        Jiri Olsa <jolsa@...hat.com>,
        Namhyung Kim <namhyung@...nel.org>,
        Andi Kleen <ak@...ux.intel.com>,
        Alexey Bayduraev <alexey.v.bayduraev@...ux.intel.com>,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH 2/5] perf record: Fix done_fd wakeup event

On Wed, Aug 24, 2022 at 12:28 AM Adrian Hunter <adrian.hunter@...el.com> wrote:
>
> evlist__add_wakeup_eventfd() calls perf_evlist__add_pollfd() to add a
> non-perf-event to the evlist pollfds. Since commit 415ccb58f68a
> ("perf record: Introduce thread specific data array") that doesn't work
> because evlist pollfs is not polled and done_fd is not duplicated into
> thread-data.
>
> Patch "perf record: Fix way of handling non-perf-event pollfds" added a new
> approach that ensures file descriptors like done_fd are handled correctly
> by flagging them as fdarray_flag__non_perf_event.
>
> Fix by flagging done_fd as fdarray_flag__non_perf_event.
>
> Example:
>
>  Before:
>
>   $ sleep 3 & perf record -vv -p $!
>   ...
>   thread_data[0x55f44bd34140]: pollfd[0] <- event_fd=5
>   thread_data[0x55f44bd34140]: pollfd[1] <- event_fd=6
>   thread_data[0x55f44bd34140]: pollfd[2] <- event_fd=7
>   thread_data[0x55f44bd34140]: pollfd[3] <- event_fd=8
>   thread_data[0x55f44bd34140]: pollfd[4] <- event_fd=9
>   thread_data[0x55f44bd34140]: pollfd[5] <- event_fd=10
>   thread_data[0x55f44bd34140]: pollfd[6] <- event_fd=11
>   thread_data[0x55f44bd34140]: pollfd[7] <- event_fd=12
>   ...
>
>  After:
>
>   $ sleep 3 & perf record -vv -p $!
>   ...
>   thread_data[0x55a8ded89140]: pollfd[0] <- event_fd=5
>   thread_data[0x55a8ded89140]: pollfd[1] <- event_fd=6
>   thread_data[0x55a8ded89140]: pollfd[2] <- event_fd=7
>   thread_data[0x55a8ded89140]: pollfd[3] <- event_fd=8
>   thread_data[0x55a8ded89140]: pollfd[4] <- event_fd=9
>   thread_data[0x55a8ded89140]: pollfd[5] <- event_fd=10
>   thread_data[0x55a8ded89140]: pollfd[6] <- event_fd=11
>   thread_data[0x55a8ded89140]: pollfd[7] <- event_fd=12
>   thread_data[0x55a8ded89140]: pollfd[8] <- non_perf_event fd=4
>   ...
>
> This patch depends on "perf record: Fix way of handling non-perf-event
> pollfds".
>
> Fixes: 415ccb58f68a ("perf record: Introduce thread specific data array")
> Signed-off-by: Adrian Hunter <adrian.hunter@...el.com>

Acked-by: Ian Rogers <irogers@...gle.com>

Thanks,
Ian

> ---
>  tools/perf/util/evlist.c | 3 ++-
>  1 file changed, 2 insertions(+), 1 deletion(-)
>
> diff --git a/tools/perf/util/evlist.c b/tools/perf/util/evlist.c
> index 48167f3941a6..0b2222d05577 100644
> --- a/tools/perf/util/evlist.c
> +++ b/tools/perf/util/evlist.c
> @@ -608,7 +608,8 @@ int evlist__filter_pollfd(struct evlist *evlist, short revents_and_mask)
>  int evlist__add_wakeup_eventfd(struct evlist *evlist, int fd)
>  {
>         return perf_evlist__add_pollfd(&evlist->core, fd, NULL, POLLIN,
> -                                      fdarray_flag__nonfilterable);
> +                                      fdarray_flag__nonfilterable |
> +                                      fdarray_flag__non_perf_event);
>  }
>  #endif
>
> --
> 2.25.1
>