linux-kernel - Re: [PATCH 3/6] perf record: add time-of-day option

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Date:	Tue, 01 Mar 2011 15:35:36 -0700
From:	David Ahern <daahern@...co.com>
To:	Peter Zijlstra <peterz@...radead.org>
CC:	linux-perf-users@...r.kernel.org, linux-kernel@...r.kernel.org,
	acme@...stprotocols.net, mingo@...e.hu, fweisbec@...il.com,
	paulus@...ba.org, tglx@...utronix.de
Subject: Re: [PATCH 3/6] perf record: add time-of-day option



On 03/01/2011 03:28 PM, Peter Zijlstra wrote:

>> And for some silly reason I sense a time trap here (pun intended) .....
>>
>> So your pushback is:
>> 1. throw out the realtime-clock event patch,
> 
> Well, no, you need continues samples to keep in sync, so having this is
> required [*].
> 
>> 2. add a new CLOCK_TRACING type to clock_gettime with VDSO hook,
> 
> Right, that is something we need anyway at some point in time.
> 
>> 3. and use a synthesized event from userspace for snapshotting
>> perf_clock to time-of-day -- similar to what I have now, but one that
>> will guarantee a time-of-day to perf_clock correlation (versus the
>> current one which hopes that perf_clock is the monotonic clock).
> 
> I guess you could do that if we have full userspace tracing support, but
> it wouldn't need synthesized events, it would need a pure userspace
> event stream.


I still don't see how this solves the need to trigger the initial sample
into the event stream.

David

> 
> Thing is, I really dislike the ioctl() trigger
> 
> 
> 
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