linux-kernel - Re: [PATCH v3.4-rc5] block: iocontext->nr

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Message-ID: <20120501185906.GE18239@redhat.com>
Date:	Tue, 1 May 2012 14:59:06 -0400
From:	Vivek Goyal <vgoyal@...hat.com>
To:	Jeff Moyer <jmoyer@...hat.com>
Cc:	Jens Axboe <jaxboe@...ionio.com>, Tejun Heo <tj@...nel.org>,
	Dave Jones <davej@...hat.com>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	Sasha Levin <levinsasha928@...il.com>
Subject: Re: [PATCH v3.4-rc5] block: iocontext->nr_tasks should be
 initialized to one

On Tue, May 01, 2012 at 02:48:41PM -0400, Jeff Moyer wrote:
> Vivek Goyal <vgoyal@...hat.com> writes:
> 
> > On Tue, May 01, 2012 at 02:31:07PM -0400, Jeff Moyer wrote:
> >
> > [..]
> >> > But as to actual users, I really don't know. I agree it's probably not
> >> > that widely used. If google still had that code search, we could get a
> >> > better idea :-)
> >> 
> >> I know of one project: the venerable dump/restore utility uses CLONE_IO.
> >
> > I thought you wrote cooperating queue logic to fix dump as it was not
> > using CLONE_IO and IO from multiple threads was going in separate 
> > queues.
> 
> That's correct.  I believe I sent the patch for dump before the kernel
> patch was accepted.  Plus, it can't hurt, right?

Ok, so now you have fixed dump to use CLONE_IO.

So only other user of coop thing remaining potentially is qemu. I was
doing some qemu testing where threads were doing IO to nearby area
but no coop merging was taking place. So not sure in practice how well
does it work. Thought, that's irrlevant for this discussion. Thought of
mentioning this observation.

Thanks
Vivek
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