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Re: [Xen-devel] [PATCH] linux-2.6.18: improve floppy behavior

from [Jeremy Fitzhardinge]

[Permanent Link][Original]

To:	Jan Beulich <JBeulich@xxxxxxxx>
Subject:	Re: [Xen-devel] [PATCH] linux-2.6.18: improve floppy behavior
From:	Jeremy Fitzhardinge <jeremy@xxxxxxxx>
Date:	Tue, 11 Oct 2011 10:14:09 -0700
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On 10/11/2011 06:41 AM, Jan Beulich wrote:
> Timing is significantly different from native both because Xen traps
> I/O port accesses and since DMA use is not possible (without intrusive
> changes). Due to the overhead of trapped port accesses, I/O is already
> slow enough (and Xen doesn't run on very old hardware anyway), so the
> situation can easily be improved by not enforcing REALLY_SLOW_IO.
>
> This doesn't completely address the issue - Xen just cannot guarantee
> scheduling of a particular vCPU with a maximum latency of about 80us
> (needed for the default FIFO threshold value of 10). The only complete
> solution would require making ISA DMA usable on Xen.

Just out of curiosity, was this in response to a real bug report or
something?

    J


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