linux-kernel - Re: [PATCH] i386 tsc: remove xtime_lock'ing around cpufreq notifier

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Message-ID: <461E8B7B.1000006@goop.org>
Date:	Thu, 12 Apr 2007 12:41:47 -0700
From:	Jeremy Fitzhardinge <jeremy@...p.org>
To:	Andi Kleen <ak@...ell.com>
CC:	Andrew Morton <akpm@...ux-foundation.org>,
	Daniel Walker <dwalker@...sta.com>,
	linux-kernel@...r.kernel.org, johnstul@...ibm.com,
	tglx@...utronix.de
Subject: Re: [PATCH] i386 tsc: remove xtime_lock'ing around cpufreq notifier

Andi Kleen wrote:
> They should always just store the cpu too and educate the users that
> only (cpu, timestamp) pairs make sense to compare.
>
> That said at least my new sched_clock should not normally show 
> large non differences between CPUs, so it can be usually ignored, but they can 
> happen. I believe some of the already existing sched_clocks() (like the
> one used on Altix) have the same property. 
>
> But on VMI/Xen as currently implemented the differences will be large.

Yes, it's pretty much unavoidable.  It seems to me that these
non-scheduler uses of sched_clock should use something else.  Or we
could add a new clock function for the scheduler to use, but
"sched_clock" seems like the best name for it.

    J
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