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

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Message-ID: <1298997435.5226.890.camel@laptop>
Date:	Tue, 01 Mar 2011 17:37:15 +0100
From:	Peter Zijlstra <peterz@...radead.org>
To:	David Ahern <daahern@...co.com>
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 Tue, 2011-03-01 at 09:09 -0700, David Ahern wrote:
> 
> I did not code it create samples of a realtime-clock event; I coded it
> to add an event to the stream on demand -- whatever event the fd is
> tied to.
> 
> 
Well yes, but aside from you and the realtime clock stuff, who'd ever
want to do this particular thing?

I'd much rather expose the whole
local_clock()/perf_clock()/trace_clock() (should all be the same anyway)
as a posix clock using CLOCK_TRACING or whatever would be an appropriate
name.

[ Since the whole thing is NMI safe it should be well possible to make a
VDSO version as well. ]

Anyway, once its visible as a posix clock you can sync up from
userspace. And this clock is indeed wanted for other things too, like
user-space tracing etc.

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