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RE: [Xen-devel] Real-time support

To: "Geoffrey Lefebvre" <geoffrey@xxxxxxxxx>, "Ky Srinivasan" <ksrinivasan@xxxxxxxxxx>
Subject: RE: [Xen-devel] Real-time support
From: "Ian Pratt" <Ian.Pratt@xxxxxxxxxxxx>
Date: Tue, 8 May 2007 21:56:44 +0100
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Thread-topic: [Xen-devel] Real-time support
> I did some basic measurements on worst case execution time inside the
> hypervisor a while ago (6-8 months ago).  From what i remember, the
> worst case where between 1-2msec on a 3GHz P4.  This was under some
> load (make -j64 bzImage).  A big culprit was the mmu-ext hypercall
> which in certain cases recursively unpins a page table. Handling
> certain page faults also took a while. This was just a preliminary
> study so i didn't push the analysis very far.

The pin/unpin operations are certainly by far the longest running
operations in Xen, and it's been on the to-do list to make them
preemptable for a long time. This should be very simple as we can exit
the hypervisor leaving the EIP on the hypercall, and next time the guest
calls in we'll pick up where we left off. 

Anyone who cares about real time on x86 up for implementing this?


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