linux-kernel - Re: [patch 07/15] sched: expire invalid runtime

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Message-ID: <1305544061.2466.4157.camel@twins>
Date:	Mon, 16 May 2011 13:07:41 +0200
From:	Peter Zijlstra <a.p.zijlstra@...llo.nl>
To:	Paul Turner <pjt@...gle.com>
Cc:	linux-kernel@...r.kernel.org,
	Bharata B Rao <bharata@...ux.vnet.ibm.com>,
	Dhaval Giani <dhaval.giani@...il.com>,
	Balbir Singh <balbir@...ux.vnet.ibm.com>,
	Vaidyanathan Srinivasan <svaidy@...ux.vnet.ibm.com>,
	Srivatsa Vaddagiri <vatsa@...ibm.com>,
	Kamalesh Babulal <kamalesh@...ux.vnet.ibm.com>,
	Ingo Molnar <mingo@...e.hu>, Pavel Emelyanov <xemul@...nvz.org>
Subject: Re: [patch 07/15] sched: expire invalid runtime

On Tue, 2011-05-03 at 02:28 -0700, Paul Turner wrote:
> With the global quota pool, one challenge is determining when the runtime we
> have received from it is still valid.  Fortunately we can take advantage of
> sched_clock synchronization around the jiffy to do this cheaply.
> 
> The one catch is that we don't know whether our local clock is behind or ahead
> of the cpu setting the expiration time (relative to its own clock).
> 
> Fortunately we can detect which of these is the case by determining whether the
> global deadline has advanced.  If it has not, then we assume we are behind, and
> advance our local expiration; otherwise, we know the deadline has truly passed
> and we expire our local runtime.

This needs a few words explaining why we need to do all this. It only e
explains the how of it.
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