linux-kernel - Re: ehci-hcd affects hda speed

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Message-Id: <200803171406.53241.david-b@pacbell.net>
Date:	Mon, 17 Mar 2008 13:06:52 -0800
From:	David Brownell <david-b@...bell.net>
To:	"Lev A. Melnikovsky" <melnikovsky@...l.ru>
Cc:	Alessandro Suardi <alessandro.suardi@...il.com>,
	Rene Herman <rene.herman@...access.nl>,
	linux-kernel@...r.kernel.org
Subject: Re: ehci-hcd affects hda speed

On Saturday 15 March 2008, Lev A. Melnikovsky wrote:
>  	Particularly, what does "MAC turn around 
> time" stand for with respect to EHCI? I would appreciate some reference, 
> thanks.

Blame VIA for that one.  Notice how their descriptions of the
fields in that register don't even mention a MAC.  :)

But the relevant bit is the "sleep time" and that's described
in the EHCI specification.  It basically means how long it waits,
after noticing a "no work for me" async schedule ring, before
scanning that schedule again.  It seems your system had that
set to just 1 usec, meaning it would hardly give anything else
a chance to get onto the PCI bus.  That's probably why the EHCI
spec uses a value of 10 usec:  basic fairness.

- Dave

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