From: Andi Kleen <ak@suse.de>
To: nagar@watson.ibm.com
Cc: Peter Chubb <peterc@gelato.unsw.edu.au>,
Andrew Morton <akpm@osdl.org>,
linux-kernel@vger.kernel.org, Ingo Molnar <mingo@elte.hu>
Subject: Re: [Patch 1/4] Delay accounting: Initialization
Date: Wed, 16 Nov 2005 02:50:22 +0100 [thread overview]
Message-ID: <200511160250.23213.ak@suse.de> (raw)
In-Reply-To: <437A8FED.3080508@watson.ibm.com>
On Wednesday 16 November 2005 02:48, Shailabh Nagar wrote:
>
> Are there problems with using sched_clock()for timestamping if one is prepared
> to live with them not necessarily being nanosecond accurate ? I'm trying to search
> the archives etc. but if you can respond with any quick comments, that'd be very
> helpful.
First it can be relatively slow on P4s (hundreds of cycles)
On other systems it can run with different frequencies on different CPUs,
so you never need to assume a timestamp from one CPU is comparable with
the one from other CPUs (the scheduler carefully avoids this)
If you need a stable timestamp over multiple CPUs don't use it.
In general do_gettimeofday is much safer.
do_gettimeofday shouldn't be that much slower for the case where TSC
works, and where it doesn't there is no other alternative.
-Andi
next prev parent reply other threads:[~2005-11-16 1:49 UTC|newest]
Thread overview: 16+ messages / expand[flat|nested] mbox.gz Atom feed top
2005-11-15 4:35 [Patch 1/4] Delay accounting: Initialization Shailabh Nagar
2005-11-15 4:20 ` Andrew Morton
2005-11-15 6:49 ` Marcelo Tosatti
2005-11-15 15:19 ` Shailabh Nagar
2005-11-15 12:20 ` Marcelo Tosatti
2005-11-15 12:34 ` Marcelo Tosatti
2005-11-15 15:08 ` Shailabh Nagar
2005-11-16 1:06 ` Peter Chubb
2005-11-16 1:48 ` Shailabh Nagar
2005-11-16 1:50 ` Andi Kleen [this message]
2005-11-16 1:52 ` Peter Chubb
2005-11-15 4:25 ` Parag Warudkar
2005-11-15 22:29 ` Shailabh Nagar
2005-11-15 22:53 ` Parag Warudkar
2005-11-16 0:45 ` Shailabh Nagar
2005-11-16 2:41 ` Parag Warudkar
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