linux-kernel - Re: [PATCH] sched: Support current clocksource handling in fallback sched

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Message-Id: <1243369815.6600.2.camel@laptop>
Date:	Tue, 26 May 2009 22:30:15 +0200
From:	Peter Zijlstra <peterz@...radead.org>
To:	john stultz <johnstul@...ibm.com>
Cc:	Linus Walleij <linus.ml.walleij@...il.com>,
	Paul Mundt <lethal@...ux-sh.org>, Ingo Molnar <mingo@...e.hu>,
	Andrew Victor <linux@...im.org.za>,
	Haavard Skinnemoen <hskinnemoen@...el.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	linux-kernel@...r.kernel.org, linux-sh@...r.kernel.org,
	linux-arm-kernel@...ts.arm.linux.org.uk,
	John Stultz <johnstul@...ux.vnet.ibm.com>,
	Thomas Gleixner <tglx@...utronix.de>
Subject: Re: [PATCH] sched: Support current clocksource handling in
 fallback sched_clock().

On Tue, 2009-05-26 at 13:23 -0700, john stultz wrote:
> Overall, I'd probably suggest thinking this through a bit more. At some
> point doing this right will cause sched_clock() to be basically the same
> as ktime_get(). So why not just use that instead of remaking it?

simply because we don't require the strict global monotonicy for
scheduling as we do from a regular time source (its nice to have
though).

That means that on x86 we can always use TSC for sched_clock(), even
when its quite unsuitable for ktime.



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