linux-kernel - Re: Why is NCQ enabled by default by libata? (2.6.20)

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Message-ID: <20070329223505.481a4f5e@the-village.bc.nu>
Date:	Thu, 29 Mar 2007 22:35:05 +0100
From:	Alan Cox <alan@...rguk.ukuu.org.uk>
To:	Phillip Susi <psusi@....rr.com>
Cc:	Jeff Garzik <jeff@...zik.org>,
	Justin Piszcz <jpiszcz@...idpixels.com>, linux@...izon.com,
	htejun@...il.com, linux-ide@...r.kernel.org,
	linux-kernel@...r.kernel.org
Subject: Re: Why is NCQ enabled by default by libata? (2.6.20)

O> writes, and sending down multiple untagged cached writes that complete 
> immediately and actually hit the disk later?  Either way the host keeps 
> sending writes to the disk until it's buffers are full, and the disk is 
> constantly trying to commit those buffers to the media in the most 
> optimal order.

On the controller side primarily you get to queue commands which means
you don't have a dead time period between the completion interrupt and
the next command being issued. Those times add up even when there is a
disk cache buffering the output
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