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Re: [PATCH v2 3/5] change number_of_cpusets to an atomic [message #46058 is a reply to message #46057]

Tue, 24 April 2012 16:24

Christoph Lameter
Messages: 123
Registered: September 2006

Senior Member

On Tue, 24 Apr 2012, Glauber Costa wrote:

> > Would this not also be a good case to introduce static branching?
> >
> > number_of_cpusets is used to avoid going through unnecessary processing
> > should there be no cpusets in use.
>
> static branches comes with a set of problems themselves, so I usually prefer
> to use them only in places where we don't want to pay even a cache miss if we
> can avoid, or a function call, or anything like that - like the slub cache
> alloc as you may have seen in my kmem memcg series.
>
> It doesn't seem to be the case here.

How did you figure that? number_of_cpusets was introduced exactly because
the functions are used in places where we do not pay the cost of calling
__cpuset_node_allowed_soft/hardwall. Have a look at these. They may take
locks etc etc in critical allocation paths

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[Message index]

		[PATCH v2 0/5] Fix problem with static_key decrement By: Glauber Costa on Mon, 23 April 2012 19:37
		[PATCH v2 1/5] don't attach a task to a dead cgroup By: Glauber Costa on Mon, 23 April 2012 19:37
		Re: [PATCH v2 1/5] don't attach a task to a dead cgroup By: KAMEZAWA Hiroyuki on Tue, 24 April 2012 02:20
		[PATCH v2 2/5] blkcg: protect blkcg->policy_list By: Glauber Costa on Mon, 23 April 2012 19:37
		[PATCH v2 3/5] change number_of_cpusets to an atomic By: Glauber Costa on Mon, 23 April 2012 19:37
		Re: [PATCH v2 3/5] change number_of_cpusets to an atomic By: KAMEZAWA Hiroyuki on Tue, 24 April 2012 02:25
		Re: [PATCH v2 3/5] change number_of_cpusets to an atomic By: Christoph Lameter on Tue, 24 April 2012 15:02
		Re: [PATCH v2 3/5] change number_of_cpusets to an atomic By: Glauber Costa on Tue, 24 April 2012 16:15
		Re: [PATCH v2 3/5] change number_of_cpusets to an atomic By: Christoph Lameter on Tue, 24 April 2012 16:24
		Re: [PATCH v2 3/5] change number_of_cpusets to an atomic By: Glauber Costa on Tue, 24 April 2012 16:30
		Re: [PATCH v2 3/5] change number_of_cpusets to an atomic By: Christoph Lameter on Tue, 24 April 2012 18:27
		[PATCH v2 4/5] don't take cgroup_mutex in destroy() By: Glauber Costa on Mon, 23 April 2012 19:37
		Re: [PATCH v2 4/5] don't take cgroup_mutex in destroy() By: KAMEZAWA Hiroyuki on Tue, 24 April 2012 02:31
		Re: [PATCH v2 4/5] don't take cgroup_mutex in destroy() By: Glauber Costa on Tue, 24 April 2012 11:42
		Re: [PATCH v2 4/5] don't take cgroup_mutex in destroy() By: Li Zefan on Wed, 25 April 2012 08:01
		[PATCH v2 5/5] decrement static keys on real destroy time By: Glauber Costa on Mon, 23 April 2012 19:37
		Re: [PATCH v2 5/5] decrement static keys on real destroy time By: KAMEZAWA Hiroyuki on Tue, 24 April 2012 02:40
		Re: [PATCH v2 5/5] decrement static keys on real destroy time By: Glauber Costa on Tue, 24 April 2012 11:41
		Re: [PATCH v2 5/5] decrement static keys on real destroy time By: KAMEZAWA Hiroyuki on Wed, 25 April 2012 00:22

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