linux-kernel - Re: QUEUE_FLAG

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Date:	Tue, 14 Oct 2008 09:54:08 +0200
From:	Jens Axboe <jens.axboe@...cle.com>
To:	Pierre Ossman <drzeus-list@...eus.cx>
Cc:	Jeff Garzik <jeff@...zik.org>, LKML <linux-kernel@...r.kernel.org>
Subject: Re: QUEUE_FLAG_NONROT and merges

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...

> 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.

-- 
Jens Axboe

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