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Date: Sun, 05 Apr 2009 16:57:21 -0400
From: Jeff Garzik <jeff@garzik.org>
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To: Mark Lord <lkml@rtr.ca>
CC: Linus Torvalds <torvalds@linux-foundation.org>,
       Theodore Tso <tytso@mit.edu>, Arjan van de Ven <arjan@infradead.org>,
       Jens Axboe <jens.axboe@oracle.com>,
       Linux Kernel Developers List <linux-kernel@vger.kernel.org>,
       Ext4 Developers List <linux-ext4@vger.kernel.org>
Subject: Re: [GIT PULL] Ext3 latency fixes
References: <alpine.LFD.2.00.0904031150190.4015@localhost.localdomain> <alpine.LFD.2.00.0904031329410.7007@localhost.localdomain> <20090404135719.GA9812@mit.edu> <20090404151649.GE5178@kernel.dk> <alpine.LFD.2.00.0904040854470.3915@localhost.localdomain> <20090404173412.GF5178@kernel.dk> <alpine.LFD.2.00.0904041039230.3915@localhost.localdomain> <20090404180108.GH5178@kernel.dk> <20090404232222.GA7480@mit.edu> <20090404163349.20df1208@infradead.org> <20090405001005.GA7553@mit.edu> <alpine.LFD.2.00.0904050927580.4023@localhost.localdomain> <49D8E71F.6000703@rtr.ca>
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Mark Lord wrote:
> Linus Torvalds wrote:
>>
>> Non-rotational media would tend to want the unplugging, but the block 
>> layer already does that (ie in __make_request() we already do:
>>
>>         if (unplug || blk_queue_nonrot(q))
>>                 __generic_unplug_device(q);
>>
>> so non-rotational devices get unplugged whether the request was a 
>> unplugging request or not).
> ..
> 
> Mmm.. except that Jeff's SSD doesn't appear to identify itself
> as a non-rotating media.  I suppose there's a way to "quirk" that
> somewhere, though.

We set it in libata-scsi.c:ata_scsi_dev_config() based on ata_id_is_ssd()

That hueristic probably assumes Intel SSDs or something :/

	Jeff