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RE: [Xen-devel] segfault in VM - FIXED!

To: Chris Andrews <chris@xxxxxxxxxx>, <xen-devel@xxxxxxxxxxxxxxxxxxxxx>
Subject: RE: [Xen-devel] segfault in VM - FIXED!
From: James Harper <JamesH@xxxxxxxxxxxxxxxx>
Date: Sun, 25 Jul 2004 19:27:24 +1000
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Thread-topic: [Xen-devel] segfault in VM - FIXED!
I'm building this now.
The way I see it, currently it must be incorrect for only a very very small number of cases or the system would crash and burn almost instantly. So in theory, unless these cases are undetectable, or the cost of detecting them is high for some reason, the performance difference should be almost unnoticable
I assume the patch would only affect dom0 and so should matter if domU is patched or not. Is there a way of installing a patch so that it's picked up by 'make world'?
i'll follow up with results shortly.

From: Chris Andrews
Sent: Sun 25/07/2004 1:54 AM
To: xen-devel@xxxxxxxxxxxxxxxxxxxxx
Subject: Re: [Xen-devel] segfault in VM - FIXED!

On 24 Jul 2004, at 13:47, I wrote:

> I'm just testing a patch which disables merging in the scsi layer when 
> it believes it has contiguous requests in different pages. I think 
> this is more pessimistic that it needs to be, as the pages may after 
> all be contiguous, but it does allow some merging  to happen and so 
> far seems to be stable.

I've given this a bit more testing, and it seems to be working fine - 
the machine is now running a dom0 kernel built while running the patch. 
As for performance, it's 'not bad' -- I've just done a bonnie++ run, 
and some compiles. Based on sticking printks in and watching the 
console, it's allowing merges much more often than not, but still I 
suspect not as much as it could. Probably it should use something with 
more arch-knowledge than page_to_phys().

patch for linux-2.4.26-xen0: 
bonnie++ stats: http://munky.nodnol.org/~chris/munkyII_stats.txt


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