linux-kernel - Re: A question about group CFS scheduling

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Date:	Thu, 26 Jun 2008 16:33:11 +0800
From:	"Zhao Forrest" <forrest.zhao@...il.com>
To:	"Peter Zijlstra" <peterz@...radead.org>
Cc:	vatsa@...ux.vnet.ibm.com, mingo@...e.hu, containers@...ts.osdl.org,
	linux-kernel@...r.kernel.org
Subject: Re: A question about group CFS scheduling

>
> Let me explain the cgroup case (the sanest option IMHO):
>
> initially all your tasks will belong to the root cgroup, eg:
>
> assuming:
> mkdir -p /cgroup/cpu
> mount none /cgroup/cpu -t cgroup -o cpu
>
> Then the root cgroup (cgroup:/) is /cgroup/cpu/ and all tasks will be
> found in /cgroup/cpu/tasks.
>
> You can then create new groups as sibling from this root group, eg:
>
> cgroup:/foo
> cgroup:/bar
>
> They will get a weigth of 1024 by default, exactly as heavy as a nice 0
> task.
>
> That means that no matter how many tasks you stuff into foo, their
> combined cpu time will be as much as a single tasks in cgroup:/ would
> get.
>
> This is fully recursive, so you can also create:
>
> cgroup:/foo/bar and its tasks in turn will get as much combined cpu time
> as a single task in cgroup:/foo would get.
>
> In theory this should go on indefinitely, in practise we'll run into
> serious numerical issues quite quickly.
>
>
> The USER grouping basically creates a fake root and all uids (including
> 0) are its siblings. The only special case is that uid-0 (aka root) will
> get twice the weight of the others.
>

Thank you for your detailed explanation! I have one more question:
cgrouping and USER grouping is mutual exclusive, am I right? That is,
when enabling cgrouping, USER grouping need to be disabled, vice
versa.

Thanks,
Forrest
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