On Thu, Oct 02, 2014 at 08:38:55PM +0400, Alexander Yarygin wrote:
> When processing events the session code has an ordered samples queue which is
> used to time-sort events coming in across multiple mmaps. At a later point in
> time samples on the queue are flushed up to some timestamp at which point the
> event is actually processed.
>
> When analyzing events live (ie., record/analysis path in the same command)
> there is a race that leads to corrupted events and parse errors which cause
> perf to terminate. The problem is that when the event is placed in the ordered
> samples queue it is only a reference to the event which is really sitting in
> the mmap buffer. Even though the event is queued for later processing the mmap
> tail pointer is updated which indicates to the kernel that the event has been
> processed. The race is flushing the event from the queue before it gets
> overwritten by some other event. For commands trying to process events live
> (versus just writing to a file) and processing a high rate of events this
> leads
> to parse failures and perf terminates.
>
> Examples hitting this problem are 'perf kvm stat live', especially with nested
> VMs which generate 100,000+ traces per second, and a command processing
> scheduling events with a high rate of context switching -- e.g., running
> 'perf bench sched pipe'.
>
> This patch offers live commands an option to copy the event when it is placed
> in
> the ordered samples queue.
>
> Based on a patch from David Ahern <dsah...@gmail.com>
>
> Signed-off-by: Alexander Yarygin <yary...@linux.vnet.ibm.com>
> Cc: Arnaldo Carvalho de Melo <a...@kernel.org>
> Cc: Christian Borntraeger <borntrae...@de.ibm.com>
> Cc: Frederic Weisbecker <fweis...@gmail.com>
> Cc: Ingo Molnar <mi...@kernel.org>
> Cc: Jiri Olsa <jo...@redhat.com>
> Cc: Mike Galbraith <efa...@gmx.de>
> Cc: Namhyung Kim <namhyung....@lge.com>
> Cc: Peter Zijlstra <a.p.zijls...@chello.nl>
> Cc: Stephane Eranian <eran...@google.com>
> ---
> tools/perf/util/ordered-events.c | 51
> ++++++++++++++++++++++++++++++++++++----
> tools/perf/util/ordered-events.h | 10 +++++++-
> tools/perf/util/session.c | 5 ++--
> 3 files changed, 58 insertions(+), 8 deletions(-)
apart from extra whitespaces (below):
Acked-by: Jiri Olsa <jo...@kernel.org>
thanks,
jirka
>
> diff --git a/tools/perf/util/ordered-events.c
> b/tools/perf/util/ordered-events.c
> index 706ce1a..06d53ee 100644
> --- a/tools/perf/util/ordered-events.c
> +++ b/tools/perf/util/ordered-events.c
SNIP
> + }
>
> pr("alloc size %" PRIu64 "B (+%zu), max %" PRIu64 "B\n",
> oe->cur_alloc_size, size, oe->max_alloc_size);
> @@ -90,15 +127,19 @@ static struct ordered_event *alloc_event(struct
> ordered_events *oe)
> pr("allocation limit reached %" PRIu64 "B\n",
> oe->max_alloc_size);
> }
>
> + new->event = new_event;
> +
> return new;
^^^ here
> }
>
> struct ordered_event *
> -ordered_events__new(struct ordered_events *oe, u64 timestamp)
> +ordered_events__new(struct ordered_events *oe, u64 timestamp,
> + union perf_event *event)
> {
> struct ordered_event *new;
>
> - new = alloc_event(oe);
> + new = alloc_event(oe, event);
> +
> if (new) {
^^^ and here
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