linux-kernel - Re: [RFC 1/4] libata: cache device select

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Message-ID: <20100218101603.23c16786@lxorguk.ukuu.org.uk>
Date:	Thu, 18 Feb 2010 10:16:03 +0000
From:	Alan Cox <alan@...rguk.ukuu.org.uk>
To:	Mark Lord <kernel@...savvy.com>
Cc:	Alan Cox <alan@...ux.intel.com>, jeff@...zik.org.com,
	linux-kernel@...r.kernel.org, linux-ide@...r.kernel.org
Subject: Re: [RFC 1/4] libata: cache device select

O> I totally agree with this patch, but question the timings used to justify it.
> Surely the overhead is only 1-2usec for the case where the device
> is the one that was already selected (on a "smart" interface) ?

IFF you have a smart interface. A lot of the controllers in the PCI space
don't appear to be that clever.

> And for the case where the currently selected device is different
> than the desired device (the 1msec case), this patch makes little/no difference?

Correct, but even with two devices per cable (which is not the most
common setup) you win. Worst case (which I've never seen) you draw.

Alan
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