From: Andi Kleen <ak@suse.de>
To: Alan Cox <alan@lxorguk.ukuu.org.uk>
Cc: linux-kernel@vger.kernel.org
Subject: Re: How is user space notified of CPU speed changes?
Date: 24 Oct 2004 01:54:46 +0200 [thread overview]
Message-ID: <p73ekjp7zy1.fsf@verdi.suse.de> (raw)
In-Reply-To: <1098566366.24804.8.camel@localhost.localdomain.suse.lists.linux.kernel>
Alan Cox <alan@lxorguk.ukuu.org.uk> writes:
> It did
>
> - The kernel doesn't always know
> - CPU speed is meaningless in hyper-threading since performance is not
> x2 for two cores but instead varies
> - It doesn't handle split CPU speed SMP - where CPU speeds vary
> - God help you if virtualised
Even without virtualization it doesn't make much sense to know the
exact CPU speed for an user process: it never knows how much CPU time
it will get (even with real time scheduling there could be even higher
priority processes)
The solution is to call gettimeofday frequently to resychronize.
It should be cheap enough that it isn't a big issue.
-Andi
next parent reply other threads:[~2004-10-23 23:54 UTC|newest]
Thread overview: 26+ messages / expand[flat|nested] mbox.gz Atom feed top
[not found] <1098399709.4131.23.camel@krustophenia.net.suse.lists.linux.kernel>
[not found] ` <1098444170.19459.7.camel@localhost.localdomain.suse.lists.linux.kernel>
[not found] ` <1098508238.13176.17.camel@krustophenia.net.suse.lists.linux.kernel>
[not found] ` <1098566366.24804.8.camel@localhost.localdomain.suse.lists.linux.kernel>
2004-10-23 23:54 ` Andi Kleen [this message]
2004-10-21 23:01 How is user space notified of CPU speed changes? Lee Revell
2004-10-22 11:23 ` Alan Cox
2004-10-22 14:12 ` Con Kolivas
2004-10-22 18:05 ` Lee Revell
2004-10-22 18:57 ` Andreas Dilger
2004-10-22 19:40 ` Chris Friesen
2004-10-22 19:46 ` Lee Revell
2004-10-22 20:28 ` Alan Cox
2004-10-22 21:46 ` Chris Friesen
2004-10-22 23:25 ` Lee Revell
2004-10-25 15:28 ` Chris Friesen
2004-10-23 5:10 ` Lee Revell
2004-10-23 10:53 ` Matthew Garrett
2004-10-23 21:19 ` Alan Cox
2004-10-23 22:42 ` Lee Revell
2004-10-23 23:17 ` Jon Masters
2004-10-24 1:40 ` Lee Revell
2004-10-24 14:02 ` Alan Cox
2004-10-26 2:38 ` Lee Revell
2004-10-26 4:05 ` Lee Revell
2004-10-23 23:35 ` Jon Masters
2004-10-23 23:36 ` Jon Masters
2004-10-24 14:04 ` Alan Cox
2004-10-25 5:53 ` Joel Becker
2004-10-24 20:02 ` Robert Love
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