linux-kernel - Re: [PATCH RFC] hist lookups

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Date:   Mon, 12 Nov 2018 00:26:27 +0100
From:   Jiri Olsa <jolsa@...hat.com>
To:     David Miller <davem@...emloft.net>
Cc:     acme@...nel.org, linux-kernel@...r.kernel.org, namhyung@...nel.org,
        jolsa@...nel.org
Subject: Re: [PATCH RFC] hist lookups

On Sun, Nov 11, 2018 at 03:08:01PM -0800, David Miller wrote:
> From: Jiri Olsa <jolsa@...hat.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@...hat.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