linux-kernel - Re: QUEUE_FLAG

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Message-ID: <20081014105425.4731de06@mjolnir.drzeus.cx>
Date:	Tue, 14 Oct 2008 10:54:25 +0200
From:	Pierre Ossman <drzeus-list@...eus.cx>
To:	Jens Axboe <jens.axboe@...cle.com>
Cc:	Jeff Garzik <jeff@...zik.org>, LKML <linux-kernel@...r.kernel.org>
Subject: Re: QUEUE_FLAG_NONROT and merges

On Tue, 14 Oct 2008 09:54:08 +0200
Jens Axboe <jens.axboe@...cle.com> wrote:

> On Tue, Oct 14 2008, Pierre Ossman wrote:
> > Hi Jeff,
> > 
> > I noticed you've added a new flag to indicate that the drive has no
> > seek costs and I figured it would be a good idea to use that on the
> > MMC/SD cards.
> 
> That was me, actually...
> 

Sorry, this was meant for you of course. I don't know how I got things
mixed up there. I guess I'll have to blame lack of coffee this
morning. :)

> > Since the name isn't entirely clear in what is implied, I just wanted
> > to check that there are no plans to assume that there is negligable
> > request overhead for queues with this flag. I.e. the flag should
> > indicate that the elevator doesn't have to care about seeks, but it
> > should still try to merge requests to reduce the transaction overhead.
> 
> Sounds about right. The flag is just meant to indicate zero-seek cost,
> as devices will still have per-command overheads, merging is still
> applicable.
> 
> So yes, you want to set that flag for mmc/sd cards, definitely.
> 

Great. I'll get a patch out ASAP.

Rgds
-- 
     -- Pierre Ossman

  Linux kernel, MMC maintainer        http://www.kernel.org
  rdesktop, core developer          http://www.rdesktop.org

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