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

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Message-ID: <4D066407.3040707@cisco.com>
Date:	Mon, 13 Dec 2010 11:20:55 -0700
From:	"David S. Ahern" <daahern@...co.com>
To:	Peter Zijlstra <peterz@...radead.org>
CC:	Arnaldo Carvalho de Melo <acme@...stprotocols.net>,
	Frederic Weisbecker <fweisbec@...il.com>,
	linux-perf-users@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 1/2] perf tools: Add reference timestamp to perf header



On 12/13/10 11:06, Peter Zijlstra wrote:
> On Mon, 2010-12-13 at 11:01 -0700, David S. Ahern wrote:
>>> Another problem with this approach is things like flight-recorder mode
>>> where you constantly over-write your old data, you'd have to build some
>>> trigger to always output a new record before you over-write the old one,
>>> so there's always one consistent record around. Drift is an even more
>>> serious problem here since flight-record more could be running for days
>>> before (if ever) you dump it.
>>
>> Ok. I was not aware flight-recorder mode was an option today.
> 
> You get it when you mmap the fd RO -- the only thing is you don't get a
> consistent tail pointer so you have to fudge a bit.

Awesome. Flight recorder mode is on our wish list. I'll try it out when
I get some time.

David

> 
> But even if we didn't have it, we'd need a solution that would work once
> we did grow it ;-)
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