Re: [Xen-devel] [PATCH][QEMU] Clear bios framebuffer with minimal writes

[Keir Fraser <Keir.Fraser@xxxxxxxxxxxx>]

On 25/10/07 16:23, "Gary Grebus" <ggrebus@xxxxxxxxxxxxxxx> wrote:

>> Is this really just a workaround for the insane-sounding case of Vista
>> clearing the screen, as described in one of the comments? Do I understand
>> correctly, and it looks like Vista does 4096 writes for each iteration of
>> the rep stosw?
> 
> Yep.  This happens when resizing the screen in Vista.  It appears to do
> this by executing the VGA BIOS code in some sort of emulation, and the
> BIOS function to clear the screen (which uses a rep stosw) gets emulated
> as 4096 separate writes.
> 
> This is so slow that occasionally some watchdog timer in Vista (that was
> timing the BIOS emulation) would expire and cause a blue screen.
> 
> This fix was a bit of a hack.  It might be possible to speed up VGA
> writes enough to make this unnecessary, but that was more of a challenge
> than I wanted at the time.

Ugh, that is awkward. Did you do this hack before the stdvga
emulation-in-xen and buffered-io patch that you guys also sent out today? I
wonder whether that speeds up vga writes enough, or whether you needed this
hack despite the speedups that other patch achieved? Overall, I guess I'm
not against this patch even though it is a bit sleazy. :-) But obviously
it's even better if the problem goes away by other means...

 -- Keir



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