Xen devel - Jul 2005 - RE: [PATCH] per-cpu time changes

Keir,

I would be interested in the interim patch.

Thanks,
Aravindh
> -----Original Message-----
> From: xen-devel-bounces@lists.xensource.com [mailto:xen-devel-
> bounces@lists.xensource.com] On Behalf Of Keir Fraser
> Sent: Saturday, July 09, 2005 5:40 AM
> To: Don Fry
> Cc: xen-devel@lists.xensource.com
> Subject: Re: [Xen-devel] [PATCH] per-cpu time changes
> 
> 
> On 8 Jul 2005, at 23:47, Don Fry wrote:
> 
> > Here is another set of patches for the per-cpu timer changes to xen
and
> > linux.  The patch is against today''s xen-unstable-src.tgz. 
This
fixes
> > the occasional panic I was seeing on booting a slower system, and
the
> > constant panic booting a fast system.  It has been tested UP and SMP
on
> > an IBM summit system, and an IntelliStation.  The ''time went
backwards''
> > messages are no longer seen.
> 
> Great! I''m cooking up a time patch to check in over the next few
days
> -- it should handle the one remaining problem I see with your patch,
> that although ''guest time'' will be monotonic on each
individual cpu,
> they will diverge over time because percpu_ticks does not update local
> time w.r.t. a shared timebase. I think solving that necessarily means
> some bigger changes to how time is handled in Xen, and the interface
to
> guests, and I''m currently merging those changes into the xenlinux
tree
> (the Xen side is done and I can post an interim patch if that''s
> interesting for anyone).
> 
>   -- Keir
> 
> 
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On 9 Jul 2005, at 15:11, Puthiyaparambil, Aravindh wrote:
> Keir,
>
> I would be interested in the interim patch.
>
> Thanks,
> Aravindh
http://www.cl.cam.ac.uk/~kaf24/xentime.diff

I removed the Linux patches because they''re still in progress, but it 
illustrates the substantial changes that were needed in Xen to ensure 
that time doesn''t go backwards, but also that all cpus stay in sync.

I also latex''ed up some of my private notes justifying and explaining 
this approach:
http://www.cl.cam.ac.uk/~kaf24/xentime.pdf

It''s very similar to what we discussed on the list a few months ago.

  -- Keir


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