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

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Message-ID: <4D065F69.7080707@cisco.com>
Date:	Mon, 13 Dec 2010 11:01:13 -0700
From:	"David S. Ahern" <daahern@...co.com>
To:	Peter Zijlstra <peterz@...radead.org>,
	Arnaldo Carvalho de Melo <acme@...stprotocols.net>
CC:	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 10:57, Peter Zijlstra wrote:
>> What about creating a PERF_RECORD_TIME and generate an event when the
>> counter is opened? It contains a PERF_SAMPLE_TIME and say
>> PERF_SAMPLE_TOD (time-of-day)? We're not sending rockets to saturn; we
>> just need the timestamps to match other log files.
> 
> That's similar to the first thing I proposed. The problem is with long
> record sessions your drift can become quite significant, then when you
> merge sort your other log events stuff can get out of order. Which can
> lead to some serious head-scratching..

Gotcha. Missed that in the flury of emails.

Arnaldo: Are you ok with this option? This should append mode as well.

> 
> 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.

David


> 
> 
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