Bug#634149: kvm extremely __slow__ under 2.6.39-2-amd64 compared to 2.6.32-5-amd64
Jonathan Nieder wrote:
> Michael Tokarev wrote:
>> So, the problem is that with this kernel commit:
>>
>> commit 7972995b0c346de76fe260ce0fd6bcc8ffab724a
>> Author: Gleb Natapov <gleb@redhat.com>
>> Date: Thu Mar 18 15:20:24 2010 +0200
>>
>> KVM: x86 emulator: Move string pio emulation into emulator.c
>[...]
>> which went into mainline with 2.6.35, there has been
>> quite some changes in PIO emulation handling in kvm
>> which resulted in correct but slow (as opposed by
>> fast but incorrect) emulation. This slowed down
>> guests that use PIO to access disks.
[...]
> That means "wishlist", and probably not worth tracking unless we want
> to document it somewhere or someone is interested in working on it,
> right?
On second thought, a regression's a regression --- going from usable
but subtly buggy to unusable is not progress. :) Maybe it would be
possible to introduce some kind of parameter to get back the speed
at the cost of correctness again?
Just musing. Sorry for the noise; I'll leave this to the experts.
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