From mboxrd@z Thu Jan  1 00:00:00 1970
From: Tejun Heo <tj-DgEjT+Ai2ygdnm+yROfE0A@public.gmane.org>
Subject: Re: [PATCH 23/24] cfq-iosched: collect stats from dead cfqgs
Date: Wed, 2 Jan 2013 11:52:42 -0500
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To: Vivek Goyal <vgoyal-H+wXaHxf7aLQT0dZR+AlfA@public.gmane.org>
Cc: lizefan-hv44wF8Li93QT0dZR+AlfA@public.gmane.org, axboe-tSWWG44O7X1aa/9Udqfwiw@public.gmane.org, containers-cunTk1MwBs9QetFLy7KEm3xJsTq8ys+cHZ5vskTnxNA@public.gmane.org, cgroups-u79uwXL29TY76Z2rM5mHXA@public.gmane.org, linux-kernel-u79uwXL29TY76Z2rM5mHXA@public.gmane.org, ctalbott-hpIqsD4AKlfQT0dZR+AlfA@public.gmane.org, rni-hpIqsD4AKlfQT0dZR+AlfA@public.gmane.org

Hey, Vivek.

On Wed, Jan 02, 2013 at 11:44:15AM -0500, Vivek Goyal wrote:
> > > In fact if we have a realiable way of resetting status then online/offline
> > > infrastructure might not be required? I think per cpu stats will be a
> > > problem though and that's why we probably require logic to online/offline
> > > the group?
> > 
> > Hmmm?  What do you mean?
> 
> I mean if we had a reliable way of resetting stats after transferring
> then we would not need to keep a track of whether group is online/offline.
> We could add everything and adding zero will not change anything. In fact
> it will also take care of residual IO (IO which happened after transfer
> of stats).

Ah... yeah, if we can do atomic transfer, we might be able to do away
with on/offlining.  Couldn't think of a way to do that without
incurring overhead to hot paths.

> Or I missed the real reason of why do we have group online/offline
> infrastructure.

But given that on/offline state is something common to cgroup, I don't
think adding the states to blkcg is a bad idea.  We need it for
reliable iterations anyways.

Thanks.

-- 
tejun