Message-ID: <41634236.1020602@pobox.com>
Date: Tue, 05 Oct 2004 20:54:14 -0400
From: Jeff Garzik <jgarzik@pobox.com>
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To: Gianluca Cecchi <gianluca.cecchi@tiscali.it>
CC: linux-kernel@vger.kernel.org
Subject: Re: Cannot enable DMA on SATA drive (SCSI-libsata, VIA SATA)
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Gianluca Cecchi wrote:
> Eventually I can provide config. Btw, I'm using udev and kernel preemption.

I strongly recommend disabling kernel preemption.  It is a hack that 
hides bugs.


> ata1: dev 0 ATA, max UDMA/133, 240121728 sectors:
> ata1: dev 0 configured for UDMA/100
> and the same for ata2?

The controller maximum is set to UDMA/100.


> But taking in parallel top with refresh 1s in another window, during the
> 80
> seconds elapsed above, I had two freezes in top session: one of 20sec and
> another
> of 15 sec: about the half of the time of the total I/O operation!
> During this time there was one cpu used at about 30%, no other cpu constraints.
> I repeated the operation with similar behaviour. Sometimes also 50 contiguos
> secs
> of freeze, until I/O operation finished.
> The freeze is not about all system itself, but only certian things.
> For example I tried also a vmstat session in another window with 3secs of
> delay
> and it had no problems while top was blocked:

Make sure you have the latest BIOS update for your system, and latest 
BIOS update for your card.

	Jeff


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