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RE: [Xen-devel] [PATCH] turn off writable page tables

To: "Andrew Theurer" <habanero@xxxxxxxxxx>, "Keir Fraser" <Keir.Fraser@xxxxxxxxxxxx>
Subject: RE: [Xen-devel] [PATCH] turn off writable page tables
From: "Ian Pratt" <m+Ian.Pratt@xxxxxxxxxxxx>
Date: Fri, 28 Jul 2006 16:51:52 +0100
Cc: Gerd Hoffmann <kraxel@xxxxxxx>, xen-devel@xxxxxxxxxxxxxxxxxxx
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Thread-index: AcayWZe2qMej3960R5Scp0aFhs9MlAARs8gA
Thread-topic: [Xen-devel] [PATCH] turn off writable page tables
> So, in summary, we know writable page tables are not broken, they just
> don't help on typical workloads because the PTEs/page are so low.
> However, they do hurt SMP guest performance.  If we are not seeing a
> benefit today, should we turn it off?  Should we make it a compile
> option, with the default off?

I wouldn't mind seeing wrpt removed altogether, or at least emulation
made the compile time default for the moment. There's bound to be some
workload that bites us in the future which is why batching updates on
the fork path mightn't be a bad thing if it can be done without too much
gratuitous hacking of linux core code.


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