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

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Date:   Sun, 11 Nov 2018 15:32:59 -0800 (PST)
From:   David Miller <davem@...emloft.net>
To:     jolsa@...hat.com
Cc:     acme@...nel.org, linux-kernel@...r.kernel.org, namhyung@...nel.org,
        jolsa@...nel.org
Subject: Re: [PATCH RFC] hist lookups

From: Jiri Olsa <jolsa@...hat.com>
Date: Mon, 12 Nov 2018 00:26:27 +0100

> 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?

It does soon after starting up, then it drops to zero.