linux-kernel - Re: [PATCH] perf record: Allow poll timeout to be specified

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Message-ID: <20150325123855.GC26966@krava.brq.redhat.com>
Date:	Wed, 25 Mar 2015 13:38:55 +0100
From:	Jiri Olsa <jolsa@...hat.com>
To:	David Ahern <david.ahern@...cle.com>
Cc:	acme@...nel.org, linux-kernel@...r.kernel.org,
	Ingo Molnar <mingo@...nel.org>,
	Frederic Weisbecker <fweisbec@...il.com>,
	Peter Zijlstra <peterz@...radead.org>,
	Jiri Olsa <jolsa@...nel.org>,
	Namhyung Kim <namhyung@...nel.org>,
	Stephane Eranian <eranian@...gle.com>,
	Adrian Hunter <adrian.hunter@...el.com>
Subject: Re: [PATCH] perf record: Allow poll timeout to be specified

On Tue, Mar 24, 2015 at 12:09:48PM -0400, David Ahern wrote:
> Record currently wakes up based on watermarks to read events from the mmaps and
> write them out to the file. The result is a file that can have large blocks of
> events per mmap before a finished round event is added to the stream.  This in
> turn affects the quantity of events that have to be passed through the ordered
> events queue before results can be displayed to the user. For commands like
> perf-script this can lead to long unnecessarily long delays before a user gets
> output. Large systems (e.g, 1024 cpus) further compound this effect. I have seen
> instances where I have to wait 45 minutes for perf-script to process a 5GB file
> before any events are shown.

so you have pipe to perf script, right?

> 
> This patch adds an option to perf-record to allow a user to specify the
> poll timeout in msec. For example using 100 msec timeouts similar to perf-top
> means the mmaps are traversed much more frequently leading to a smoother
> analysis side.

there's also the '--no-buffering' option that sets:

                attr->watermark = 0;
                attr->wakeup_events = 1;

but that's just the other edge, which is not what you'd want

I think it's good to have user side configurable as well

Acked-by: Jiri Olsa <jolsa@...nel.org>

thanks,
jirka
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