linux-kernel - Re: [PATCH v5] sched: Avoid unnecessary work in reweight

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Message-ID: <20120227041259.GA2331@linux.vnet.ibm.com>
Date:	Mon, 27 Feb 2012 09:42:59 +0530
From:	Srivatsa Vaddagiri <vatsa@...ux.vnet.ibm.com>
To:	Michael Wang <wangyun@...ux.vnet.ibm.com>
Cc:	Peter Zijlstra <a.p.zijlstra@...llo.nl>,
	Ingo Molnar <mingo@...e.hu>,
	LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v5] sched: Avoid unnecessary work in reweight_entity

* Michael Wang <wangyun@...ux.vnet.ibm.com> [2012-02-25 21:56:18]:

> Hi, Peter
> 
> I have collected more testing data, here is the test results:
> 
> Machine:	ThinkPad T420
> OS:		Ubuntu 11.10
> Benchmark:	time make -j14 (build kernel)

Is that benchmark run in root (cpu) cgroup? If so, reweight_entity() should not
kick in at all.

static void update_cfs_shares(struct cfs_rq *cfs_rq)
{

        ..

        if (!se || throttled_hierarchy(cfs_rq))
                return;

        ..

	reweight_entity();
}

If you want to stress reweight_entity() create several (cpu) cgroups
and launch workload like kernbench in each of them ..

- vatsa

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