linux-kernel - Re: [CFS Bandwidth Control v4 5/7] sched: add exports tracking cfs bandwidth control statistics

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Date:	Wed, 23 Feb 2011 14:32:12 +0100
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@...ux.vnet.ibm.com>,
	Balbir Singh <balbir@...ux.vnet.ibm.com>,
	Vaidyanathan Srinivasan <svaidy@...ux.vnet.ibm.com>,
	Gautham R Shenoy <ego@...ibm.com>,
	Srivatsa Vaddagiri <vatsa@...ibm.com>,
	Kamalesh Babulal <kamalesh@...ux.vnet.ibm.com>,
	Ingo Molnar <mingo@...e.hu>,
	Pavel Emelyanov <xemul@...nvz.org>,
	Herbert Poetzl <herbert@...hfloor.at>,
	Avi Kivity <avi@...hat.com>,
	Chris Friesen <cfriesen@...tel.com>,
	Nikhil Rao <ncrao@...gle.com>
Subject: Re: [CFS Bandwidth Control v4 5/7] sched: add exports tracking cfs
 bandwidth control statistics

On Tue, 2011-02-15 at 19:18 -0800, Paul Turner wrote:
> +       raw_spin_lock(&cfs_b->lock);
> +       cfs_b->throttled_time += (rq->clock - cfs_rq->throttled_timestamp);
> +       raw_spin_unlock(&cfs_b->lock); 

That seems to put the cost of things on the wrong side. Read is rare,
update is frequent, and you made the frequent thing the most expensive
one.


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