Subject: Re: Strange IO behaviour on wakeup from sleep
From: Benjamin Herrenschmidt <benh@kernel.crashing.org>
To: Zachary Amsden <zach@vmware.com>
Cc: Linux Kernel list <linux-kernel@vger.kernel.org>
In-Reply-To: <417FAE3F.20908@vmware.com>
References: <417FAE3F.20908@vmware.com>
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Date: Thu, 28 Oct 2004 08:40:31 +1000
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On Wed, 2004-10-27 at 07:18 -0700, Zachary Amsden wrote:

> I would tend to be very suspicious of DMA not being restored correctly 
> because on some systems, prior to or during suspend, DMA may be shutdown 
> to conserve power.  There are changes afloat that touch suspend/resume, 
> and there have been historical problems with DMA not being restored 
> properly after wakeup on some laptops.

DMA is restored, and the resulting is way slower than what PIO would
explain anyway. I get less than 100Kb/sec !

(I wrote the IDE suspend/resume code and the driver for this chipset, so
I'm fairly sure that side is ok, it didn't change for a while, but I'll
double check in case Bart latest updates broke something).

> Although this may be another shot in the dark, it might rule out the DMA 
> problem:  try cat /proc/ide/yourchipset before and after suspend and 
> note any changes.  Failing that, use hdparm to turn off DMA before 
> suspend and see if the performance suffers to the same degree as after 
> wakeup.

Tried all of that.

Ben.


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