Subject: Re: [patch 07/15] sched: expire invalid runtime
From: Peter Zijlstra <a.p.zijlstra@chello.nl>
To: Paul Turner <pjt@google.com>
Cc: linux-kernel@vger.kernel.org, Bharata B Rao <bharata@linux.vnet.ibm.com>,
        Dhaval Giani <dhaval.giani@gmail.com>,
        Balbir Singh <balbir@linux.vnet.ibm.com>,
        Vaidyanathan Srinivasan <svaidy@linux.vnet.ibm.com>,
        Srivatsa Vaddagiri <vatsa@in.ibm.com>,
        Kamalesh Babulal <kamalesh@linux.vnet.ibm.com>,
        Ingo Molnar <mingo@elte.hu>, Pavel Emelyanov <xemul@openvz.org>
In-Reply-To: <20110503092905.075386331@google.com>
References: <20110503092846.022272244@google.com>
	 <20110503092905.075386331@google.com>
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Date: Mon, 16 May 2011 13:07:41 +0200
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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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