linux-kernel - Re: [PATCH] block: export SSD/non-rotational queue flag through sysfs

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Message-ID: <20090203133242.29904063@mjolnir.drzeus.cx>
Date:	Tue, 3 Feb 2009 13:32:42 +0100
From:	Pierre Ossman <drzeus-list@...eus.cx>
To:	Jens Axboe <jens.axboe@...cle.com>
Cc:	Hugh Dickins <hugh@...itas.com>,
	James Bottomley <James.Bottomley@...senPartnership.com>,
	Grant Grundler <grundler@...gle.com>,
	Greg Freemyer <greg.freemyer@...il.com>,
	Tejun Heo <htejun@...il.com>, Michael Tokarev <mjt@....msk.ru>,
	Kay Sievers <kay.sievers@...y.org>,
	Bartlomiej Zolnierkiewicz <bzolnier@...il.com>,
	linux-kernel@...r.kernel.org, linux-ide@...r.kernel.org,
	Alan Cox <alan@...rguk.ukuu.org.uk>
Subject: Re: [PATCH] block: export SSD/non-rotational queue flag through
 sysfs

On Fri, 16 Jan 2009 07:48:18 +0100
Jens Axboe <jens.axboe@...cle.com> wrote:

> 
> For non-queuing devices, I think our current check is a bit too drastic.
> We probably want to change that to
> 
> int dont_plug(q)
> {
>         return blk_queue_nonrot(q) && blk_queue_tagged(q);
> }
> 

Please do. The MMC block driver sets nonrot as of late, but it is
extremely dependent on merging. The command overhead is just silly, so
to get anywhere near the speed numbers indicated in marketing you need
large requests.

It seems that too many confuse "non-rotational" with "low latency",
which isn't always the same. :)

Rgds
-- 
     -- Pierre Ossman

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

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