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

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Date:	Wed, 25 Mar 2015 08:41:07 -0600
From:	David Ahern <david.ahern@...cle.com>
To:	Arnaldo Carvalho de Melo <acme@...nel.org>,
	Ingo Molnar <mingo@...nel.org>
CC:	linux-kernel@...r.kernel.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 3/25/15 6:14 AM, Arnaldo Carvalho de Melo wrote:
> If David doesn't come up with something I'll probably will, as making
> 'trace' use the ordered_samples, like 'perf top' does (initially with
> some arbitrary reasonable poll timeout value), is a low hanging fruit to
> get those multi-CPU tracepoints sorted until I get something better in
> place...

I have thought about it. It needs to be an adaptive algorithm:
1. start at 100 msec.
2. Read the maps. How much data are there (not events, but data size)? 
3. Adjust poll timeout up or down with some heuristic -- maybe something 
similar to the algorithm perf-top uses for removing entries from the 
histograms.

That said, I still thinking giving the user control is not a crazy idea.

David
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