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From: Jens Axboe <jens.axboe@oracle.com>
To: Andrew Morton <akpm@linux-foundation.org>
Cc: Paul Clements <paul.clements@steeleye.com>,
	randy.dunlap@oracle.com, linux-kernel@vger.kernel.org
Subject: Re: [PATCH 1/1] NBD: make nbd default to deadline I/O scheduler
Date: Tue, 19 Feb 2008 10:19:43 +0100	[thread overview]
Message-ID: <20080219091943.GS23197@kernel.dk> (raw)
In-Reply-To: <20080218155001.97bf5976.akpm@linux-foundation.org>

On Mon, Feb 18 2008, Andrew Morton wrote:
> On Mon, 18 Feb 2008 19:16:30 +0100 Jens Axboe <jens.axboe@oracle.com> wrote:
> 
> > On Tue, Feb 12 2008, Andrew Morton wrote:
> > > On Sat, 09 Feb 2008 08:30:40 -0500
> > > Paul Clements <paul.clements@steeleye.com> wrote:
> > > 
> > > > +		old_e = disk->queue->elevator;
> > > > +		if (elevator_init(disk->queue, "deadline") == 0 ||
> > > > +			elevator_init(disk->queue, "noop") == 0) {
> > > > +				elevator_exit(old_e);
> > > > +		}
> > > >  	}
> > > 
> > > afacit elevator_init() will not trigger a request_module().  And you really
> > > do want to trigger the request_module() here.  Perhaps the block layer
> > > should provide a means of doing so?
> > 
> > Good point, I think elevator_get() should do that automatically. Does
> > this look sane?
> > 
> > diff --git a/block/elevator.c b/block/elevator.c
> > index bafbae0..88318c3 100644
> > --- a/block/elevator.c
> > +++ b/block/elevator.c
> > @@ -134,6 +134,21 @@ static struct elevator_type *elevator_get(const char *name)
> >  	spin_lock(&elv_list_lock);
> >  
> >  	e = elevator_find(name);
> > +	if (!e) {
> > +		char elv[ELV_NAME_MAX + strlen("-iosched")];
> > +
> > +		spin_unlock(&elv_list_lock);
> > +
> > +		if (!strcmp(name, "anticipatory"))
> > +			sprintf(elv, "as-iosched");
> > +		else
> > +			sprintf(elv, "%s-iosched", name);
> > +
> > +		request_module(elv);
> > +		spin_lock(&elv_list_lock);
> > +		e = elevator_find(name);
> > +	}
> > +
> >  	if (e && !try_module_get(e->elevator_owner))
> >  		e = NULL;
> 
> Looks nice and simple.  There might be some of the usual ordering problems
> when this is called during boot, maybe is-initramfs-available-yet problems,
> etc.  But it's unlikely to make things regress from where they are now.

Isn't request_module() and below robust enough to handle that?

> Should we emit a warning if the desired elevator wasn't available?

Hmm, not sure. Either the request came from a driver, in which case
it'll be notified that we could not load that elevator. Or it'll come
through sysfs online switching, in which case we already print a
warning.

-- 
Jens Axboe


  reply	other threads:[~2008-02-19  9:20 UTC|newest]

Thread overview: 17+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2008-02-08 16:47 Paul Clements
2008-02-08 17:33 ` Randy Dunlap
2008-02-08 18:11   ` Andrew Morton
2008-02-08 18:41     ` Paul Clements
2008-02-08 20:45       ` Jens Axboe
2008-02-08 20:47         ` Jens Axboe
2008-02-08 21:23           ` Paul Clements
2008-02-08 22:02             ` Andrew Morton
2008-02-09 13:30               ` Paul Clements
2008-02-12 23:16                 ` Andrew Morton
2008-02-18 18:16                   ` Jens Axboe
2008-02-18 23:50                     ` Andrew Morton
2008-02-19  9:19                       ` Jens Axboe [this message]
2008-02-19  9:24                         ` Jens Axboe
2008-02-19 10:02                           ` Andrew Morton
2008-02-19 10:05                             ` Jens Axboe
2008-02-08 22:45       ` [Nbd] " Mike Snitzer

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