Re: [Qemu-devel] Boot Problems Windows XP guest

[Paolo Bonzini <pbonzini@redhat.com>]

Il 28/08/2013 11:07, Erik Rull ha scritto:
>>> It could be a real difference, actually.  An unexpectedly fast disk
>>> might screw a sloppy driver.  IIRC you're not the first person reporting
>>> it.  Stefan, do you think using block throttling could fix it (with some
>>> trial and error)?
>>
>> That might work.  You could start with something like -drive ...,iops=20
>> and then disable the limit from the QEMU monitor once the guest OS is
>> booting (block_set_io_throttle virtio0 0 0 0 0 0 0).
>>
>> It would be easier to try -drive ...,cache=writethrough and -win2k-hack
>> first as Anthony suggests.
>>
>> Stefan
> 
> Thanks.
> I tried that, but when should I reset the throttle?

Never.  The bug will be there through the whole execution of the guest.

> When I reset it some seconds
> after the BIOS screen disappeared same result as without throttling. When I keep
> it, Windows still reboots, the cycle just takes longer (half an hour), but the
> progress seems to be the same as without throttle.

On second thought that is expected.  Until throttling kicks in, I/O will
complete just as fast as without throttling.  Maybe limiting the number
of bytes per second instead of I/O ops would be better.  Can you try
-drive ...,bps=1048576 (possibly higher or lower numbers too)?

And maybe Benoit's new algorithm could help too.  Benoit, do you have a
tree for Erik to try?

Paolo