linux-kernel - Re: [ckrm-tech] [PATCH 0/2] resource control file system

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Message-ID: <20070305173401.GA17044@in.ibm.com>
Date:	Mon, 5 Mar 2007 23:04:01 +0530
From:	Srivatsa Vaddagiri <vatsa@...ibm.com>
To:	Paul Jackson <pj@....com>, ckrm-tech@...ts.sourceforge.net,
	linux-kernel@...r.kernel.org, xemul@...ru, ebiederm@...ssion.com,
	winget@...gle.com, containers@...ts.osdl.org, menage@...gle.com,
	akpm@...ux-foundation.org
Subject: Re: [ckrm-tech] [PATCH 0/2] resource control file system - aka containers on top of nsproxy!

On Sat, Mar 03, 2007 at 06:32:44PM +0100, Herbert Poetzl wrote:
> > Yes, perhaps this overloads nsproxy more than what it was intended for.
> > But, then if we have to to support resource management of each
> > container/vserver (or whatever group is represented by nsproxy),
> > then nsproxy seems the best place to store this resource control 
> > information for a container.
> 
> well, the thing is, as nsproxy is working now, you
> will get a new one (with a changed subset of entries)
> every time a task does a clone() with one of the 
> space flags set, which means, that you will end up
> with quite a lot of them, but resource limits have
> to address a group of them, not a single nsproxy
> (or act in a deeply hierarchical way which is not
> there atm, and probably will never be, as it simply
> adds too much overhead)

Thats why nsproxy has pointers to resource control objects, rather than
embedding resource control information in nsproxy itself.

>From the patches:

struct nsproxy {

+#ifdef CONFIG_RCFS
+       struct list_head list;
+       void *ctlr_data[CONFIG_MAX_RC_SUBSYS];
+#endif

}

This will let different nsproxy structures share the same resource
control objects (ctlr_data) and thus be governed by the same parameters.

Where else do you think the resource control information for a container
should be stored?

> > It should have the same perf overhead as the original
> > container patches (basically a double dereference -
> > task->containers/nsproxy->cpuset - required to get to the 
> > cpuset from a task).
> 
> on every limit accounting or check? I think that
> is quite a lot of overhead ...

tsk->nsproxy->ctlr_data[cpu_ctlr->id]->limit (4 dereferences) is what we 
need to get to the cpu b/w limit for a task.

If cpu_ctlr->id is compile time decided, then that would reduce it to 3.

But I think if CPU scheduler schedules tasks from same container one
after another (to the extent possible that is), then other derefences
(->ctlr_data[] and ->limit) should be fast, as they should be in the cache?


-- 
Regards,
vatsa
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