linux-kernel - Re: [PATCH 1/2] perf tools: Add reference timestamp to perf header

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Date:	Mon, 13 Dec 2010 19:10:24 +0100
From:	Peter Zijlstra <a.p.zijlstra@...llo.nl>
To:	Frederic Weisbecker <fweisbec@...il.com>
Cc:	Arnaldo Carvalho de Melo <acme@...stprotocols.net>,
	"David S. Ahern" <daahern@...co.com>,
	linux-perf-users@...r.kernel.org, linux-kernel@...r.kernel.org,
	Thomas Gleixner <tglx@...utronix.de>
Subject: Re: [PATCH 1/2] perf tools: Add reference timestamp to perf header

On Mon, 2010-12-13 at 19:05 +0100, Frederic Weisbecker wrote:
> 
> There is one writer per cpu and a (stupid) multiplexing at report time.
> It was working. Just the sorting on report time was (stupidly) slow.
> 
> I should perhaps rebase that branch and try to make something with it. 

Right, so we need to have a small ~16 events sort window per file [*],
and then a merge-sort over all files, simply consumer the most recent
event across all files.

We can have out-of-order events on a single cpu due to nesting and
taking the time-stamp _before_ we reserve the buffer. We could cure some
of this by moving the perf_clock() call from
__perf_event_header__init_id()/perf_prepare_sample() to
__perf_event_output_id_sample()/perf_output_sample().

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