linux-kernel - Re: [patch 07/16] sched: expire invalid runtime

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Date:	Wed, 22 Jun 2011 18:38:55 +0900
From:	Hidetoshi Seto <seto.hidetoshi@...fujitsu.com>
To:	Paul Turner <pjt@...gle.com>
CC:	linux-kernel@...r.kernel.org,
	Peter Zijlstra <a.p.zijlstra@...llo.nl>,
	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 07/16] sched: expire invalid runtime

(2011/06/21 16:16), Paul Turner wrote:
> Since quota is managed using a global state but consumed on a per-cpu basis
> we need to ensure that our per-cpu state is appropriately synchronized.  
> Most importantly, runtime that is state (from a previous period) should not be
> locally consumable.
> 
> We take advantage of existing sched_clock synchronization about the jiffy to
> efficiently detect whether we have (globally) crossed a quota boundary above.
> 
> One catch is that the direction of spread on sched_clock is undefined, 
> specifically, we don't know whether our local clock is behind or ahead
> of the one responsible for the current expiration time.
> 
> Fortunately we can differentiate these by considering whether the
> global deadline has advanced.  If it has not, then we assume our clock to be 
> "fast" and advance our local expiration; otherwise, we know the deadline has
> truly passed and we expire our local runtime.
> 
> Signed-off-by: Paul Turner <pjt@...gle.com>
> Reviewed-by: Hidetoshi Seto <seto.hidetoshi@...fujitsu.com>
> 
> ---

Reviewed-by: Hidetoshi Seto <seto.hidetoshi@...fujitsu.com>


Thanks,
H.Seto

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