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Re: [Xen-devel] xen-unstable, winxp32 very poor performance on AMD FX-8150, I bisected and changeset is 24770:7f79475d3de7

On 10/22/2012 03:59 PM, Tim Deegan wrote:
> At 19:21 +0200 on 20 Oct (1350760876), Peter Maloney wrote:
>> I ran a bisect to find out when Windows XP 32 bit becomes unusably slow.
>> And I found the changeset that caused it.
>> ==========
>> The problem:
>> ==========
>> Windows 8 64 bit and 32 bit run fast and fine in the newest xen versions.
>> Windows XP 32 bit runs unusably slow in anything new that I built from
>> xen-unstable, but runs fast in 4.1.2 and 4.1.3 stable. While it is
>> running slow, "xm top" or "xl top" show cpu usage around 650% for the domu.
>> The bug might be AMD specific. I'm running an AMD FX-8150.
> The bug does seem to be AMD-specific, and NPT-specific; with
> 'hap=0' it goes much faster. 
K. glad to hear it  ;) I just guessed it was AMD specific since not so
many of us seem to run AMDs and it seemed to be only me with the problem.
>> ==========
>> The result:
>> ==========
>> good: 24769:730f6ed72d70
>> bad: 24770:7f79475d3de7
>> The change was 8 months ago
>> changeset:   24770:7f79475d3de7
>> user:        Andres Lagar-Cavilla <andres@xxxxxxxxxxxxxxxx>
>> date:        Fri Feb 10 16:07:07 2012 +0000
>> summary:     x86/mm: Make p2m lookups fully synchronized wrt modifications
> This change was bad for performnace across the board and most of it has
> since been either reverted or amended, but clearly we missed something
> here. 
> It's interesting that Win8 isn't slowed down.  I wonder whether that's to
> do with the way it drives the VGA card -- IIRC it uses a generic VESA
> driver rather than a Cirrus one. 
My tests included
- passthrough and "stdvga=1" which replaces the cirrus one with some
other card.
- no passthrougn, and did not set stdvga (used vnc and cirrus)
Both were slow.
> Tim.
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