linux-kernel - Re: [PATCH 05/10] block: remove per-queue plugging

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Message-ID: <20110422161016.GC8255@redhat.com>
Date:	Fri, 22 Apr 2011 12:10:16 -0400
From:	Vivek Goyal <vgoyal@...hat.com>
To:	"hch@...radead.org" <hch@...radead.org>
Cc:	Jens Axboe <jaxboe@...ionio.com>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 05/10] block: remove per-queue plugging

On Fri, Apr 22, 2011 at 12:01:10PM -0400, Vivek Goyal wrote:
> On Fri, Apr 22, 2011 at 11:39:08AM -0400, hch@...radead.org wrote:
> > On Mon, Apr 18, 2011 at 05:23:06PM -0400, hch@...radead.org wrote:
> > > > NeilBrown (6):
> > > >       md: use new plugging interface for RAID IO.
> > > >       md/dm - remove remains of plug_fn callback.
> > > >       md - remove old plugging code.
> > > >       md: provide generic support for handling unplug callbacks.
> > > >       md: incorporate new plugging into raid5.
> > > >       md: fix up raid1/raid10 unplugging.
> > > 
> > > Looking over more of the unplugging left over, is there a reason to
> > > keep the unplug_work bits in CFQ?  They seem to rather counter the
> > > current scheme (and it is the last user of kblockd outside of
> > > blk-core.c)
> > 
> > Jens, Vivkek:
> > 
> > can you take a look at if cfq_schedule_dispatch is still needed in
> > new unplugging world order?  It's the only kblockd user outside the
> > block core that's still left, and it seems rather odd to me at least.
> 
> I guess cfq_schedule_dispatch() will still be required. One use case is
> that CFQ might not dispatch requests to driver even if it has one (idling on
> cfqq) and once the timer fires, it still need to be able to kick the queue
> and dispatch requests.
> 
> To me this sounds independent of plugging logic. Or am I missing something.

I guess you question probably was that do we still need cfqd->unplug_work
and cfq_kick_queue() and can these be replaced by delay_work mechanism.
I think would think that we should be able to. Will wirte a patch and
test it.

Thanks
Vivek
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