linux-ext4 - Re: Is TRIM/DISCARD going to be a performance problem?

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Date:	Mon, 11 May 2009 11:43:44 -0400
From:	Jeff Garzik <jeff@...zik.org>
To:	Jens Axboe <jens.axboe@...cle.com>
CC:	Jörn Engel <joern@...fs.org>,
	Theodore Tso <tytso@....edu>,
	Matthew Wilcox <willy@...ux.intel.com>,
	Ric Wheeler <rwheeler@...hat.com>,
	linux-fsdevel@...r.kernel.org, linux-ext4@...r.kernel.org
Subject: Re: Is TRIM/DISCARD going to be a performance problem?

Jens Axboe wrote:
>>> The only problem with SSD's is the people who designed the ATA TRIM
>>> command requires us to completely drian the I/O queue before issuing
>>> it.  Because of this incompetence, we need to be a bit more careful
>>> about how we issue them.
>> And this bit that I wasn't aware of.  Such a requirement in the standard
>> is a trainwreck indeed.
> 
> Precisely, but that's how basically anything works with SATA NCQ, only
> read/write dma commands may be queued. Anything else requires an idle
> drive before issue.

Very true -- but FWIW, one option being considered at T13 is having a 
queue-able TRIM.

	Jeff


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