From: Balbir Singh <balbir@linux.vnet.ibm.com>
To: Vivek Goyal <vgoyal@redhat.com>
Cc: Jens Axboe <jaxboe@fusionio.com>,
linux kernel mailing list <linux-kernel@vger.kernel.org>,
Gui Jianfeng <guijianfeng@cn.fujitsu.com>,
KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>,
Li Zefan <lizf@cn.fujitsu.com>,
Nauman Rafique <nauman@google.com>,
"Daniel P. Berrange" <berrange@redhat.com>
Subject: Re: [RFC] blk-cgroup: Allow creation of hierarchical cgroups
Date: Wed, 3 Nov 2010 07:57:33 +0530 [thread overview]
Message-ID: <20101103022733.GJ3769@balbir.in.ibm.com> (raw)
In-Reply-To: <20101102222030.GI7198@redhat.com>
* Vivek Goyal <vgoyal@redhat.com> [2010-11-02 18:20:30]:
> o Allow hierarchical cgroup creation for blkio controller
>
> o Currently we disallow it as both the io controller policies (throttling
> as well as proportion bandwidth) do not support hierarhical accounting
> and control. But the flip side is that blkio controller can not be used with
> libvirt as libvirt creates a cgroup hierarchy deeper than 1 level.
>
> <top-level-cgroup-dir>/<controller>/libvirt/qemu/<virtual-machine-groups>
>
> o So this patch will allow creation of cgroup hierarhcy but at the backend
> everything will be treated as flat. So if somebody created a an hierarchy
> like as follows.
>
> root
> / \
> test1 test2
> |
> test3
>
> CFQ and throttling will practically treat all groups at same level.
>
> pivot
> / | \ \
> root test1 test2 test3
>
> o Once we have actual support for hierarchical accounting and control
> then we can introduce another cgroup tunable file "blkio.use_hierarchy"
> which will be 0 by default but if user wants to enforce hierarhical
> control then it can be set to 1. This way there should not be any
> ABI problems down the line.
>
> o The only not so pretty part is introduction of extra file "use_hierarchy"
> down the line. Kame-san had mentioned that hierarhical accounting is
> expensive in memory controller hence they keep it off by default. I
> suspect same will be the case for IO controller also as for each IO
> completion we shall have to account IO through hierarchy up to the root.
> if yes, then it probably is not a very bad idea to introduce this extra
> file so that it will be used only when somebody needs it and some people
> might enable hierarchy only in part of the hierarchy.
>
> o This is how basically memory controller also uses "use_hierarhcy" and
> they also allowed creation of hierarchies when actual backend support
> was not available.
>
> Signed-off-by: Vivek Goyal <vgoyal@redhat.com>
Acked-by: Balbir Singh <balbir@linux.vnet.ibm.com>
--
Three Cheers,
Balbir
next prev parent reply other threads:[~2010-11-03 2:27 UTC|newest]
Thread overview: 9+ messages / expand[flat|nested] mbox.gz Atom feed top
2010-11-02 22:20 [RFC] blk-cgroup: Allow creation of hierarchical cgroups Vivek Goyal
2010-11-03 0:11 ` Chad Talbott
2010-11-03 13:26 ` Vivek Goyal
2010-11-03 2:27 ` Balbir Singh [this message]
2010-11-03 4:14 ` Gui Jianfeng
2010-11-03 15:03 ` Ciju Rajan K
2010-11-15 15:28 ` Vivek Goyal
2010-11-15 18:38 ` Jens Axboe
2010-11-16 2:50 ` KAMEZAWA Hiroyuki
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