linux-kernel - Re: [PATCH mmotm 2.5/4] memcg: disable irq at page cgroup lock (Re: [PATCH -mmotm 3/4] memcg: dirty pages accounting and limiting infrastructure)

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Message-ID: <20100310035624.GP3073@balbir.in.ibm.com>
Date:	Wed, 10 Mar 2010 09:26:24 +0530
From:	Balbir Singh <balbir@...ux.vnet.ibm.com>
To:	Daisuke Nishimura <nishimura@....nes.nec.co.jp>
Cc:	linux-mm@...ck.org, Andrea Righi <arighi@...eler.com>,
	linux-kernel@...r.kernel.org,
	Trond Myklebust <trond.myklebust@....uio.no>,
	Suleiman Souhlal <suleiman@...gle.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	containers@...ts.linux-foundation.org,
	Vivek Goyal <vgoyal@...hat.com>
Subject: Re: [PATCH mmotm 2.5/4] memcg: disable irq at page cgroup lock (Re:
 [PATCH -mmotm 3/4] memcg: dirty pages accounting and limiting
 infrastructure)

* nishimura@....nes.nec.co.jp <nishimura@....nes.nec.co.jp> [2010-03-10 10:43:09]:

> > Please please measure the performance overhead of this change.
> > 
> 
> here.
> 
> > > > > > > I made a patch below and measured the time(average of 10 times) of kernel build
> > > > > > > on tmpfs(make -j8 on 8 CPU machine with 2.6.33 defconfig).
> > > > > > > 
> > > > > > > <before>
> > > > > > > - root cgroup: 190.47 sec
> > > > > > > - child cgroup: 192.81 sec
> > > > > > > 
> > > > > > > <after>
> > > > > > > - root cgroup: 191.06 sec
> > > > > > > - child cgroup: 193.06 sec
> > > > > > > 
> 
> <after2(local_irq_save/restore)>
> - root cgroup: 191.42 sec
> - child cgroup: 193.55 sec
> 
> hmm, I think it's in error range, but I can see a tendency by testing several times
> that it's getting slower as I add additional codes. Using local_irq_disable()/enable()
> except in mem_cgroup_update_file_mapped(it can be the only candidate to be called
> with irq disabled in future) might be the choice.
>

Error range would depend on things like standard deviation and
repetition. It might be good to keep update_file_mapped and see the
impact. My concern is with large systems, the difference might be
larger.
 
-- 
	Three Cheers,
	Balbir
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