Re: [PATCH RFC] hist lookups

Jiri Olsa
2018-11-11T23:26:32Z

On Sun, Nov 11, 2018 at 03:08:01PM -0800, David Miller wrote:
> From: Jiri Olsa <jolsa@redhat.com>
> Date: Sun, 11 Nov 2018 20:41:32 +0100
>
> > On Thu, Nov 08, 2018 at 05:07:21PM -0800, David Miller wrote:
> >> From: Jiri Olsa <jolsa@redhat.com>
> >> Date: Thu, 8 Nov 2018 08:13:03 +0100
> >>
> >> > we could separated fork/mmaps to separate dummy event map, or just
> >> > parse them out in the read thread and create special queue for them
> >> > and drop just samples in case we are behind
> >>
> >> What you say at the end here is basically what I am proposing.
> >>
> >> Perf dequeues events from mmap ring as fast as possible.
> >>
> >> Perf has two internal queues, high priority and low priority.
> >>
> >> High priority events are never dropped.
> >>
> >> Low priority events are dropped on overload, oldest first.
> >
> > I added the dropping logic, it's simple so far..
>
> So for me perf top gets into a state where the samples counter stops
> incrementing, but the event counter does keep moving (which is the
> histogram code decaying histogram entries from the display thread).
>
> Which means the event processing has basically stopped.
>
> The event threads are not stuck in a loop, because they respond to
> the "q" keypress and we can exit.

is the drop count showing something?

jirka