linux-kernel - Re: [patch 11/15] sched: hierarchical task accounting for SCHED

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Date:	Tue, 05 Apr 2011 15:28:10 +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 11/15] sched: hierarchical task accounting for
 SCHED_OTHER

On Tue, 2011-03-22 at 20:03 -0700, Paul Turner wrote:
> With task entities participating in throttled sub-trees it is possible for
> task activation/de-activation to not lead to root visible changes to
> rq->nr_running.  This in turn leads to incorrect idle and weight-per-task load
> balance decisions.
> 
> To allow correct accounting we move responsibility for updating rq->nr_running
> to the respective sched::classes.  In the fair-group case this update is
> hierarchical, tracking the number of active tasks rooted at each group entity.
> 
> This also allows us to fix a small buglet in pick_next_task() when group
> scheduling is enabled.
> 
> Note: technically this issue also exists with the existing sched_rt
> throttling; however due to the nearly complete provisioning of system
> resources for rt scheduling this is much less common by default.

Shouldn't this patch live at the start of the series?


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