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Re: [Xen-devel] Is patches/linux-2.6.18/xen-hotplug.patch still necessar

To: Keir Fraser <keir@xxxxxxxxxxxxx>
Subject: Re: [Xen-devel] Is patches/linux-2.6.18/xen-hotplug.patch still necessary?
From: Alex Williamson <alex.williamson@xxxxxx>
Date: Wed, 09 May 2007 09:38:00 -0600
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On Wed, 2007-05-09 at 16:32 +0100, Keir Fraser wrote:
> On 9/5/07 16:07, "Alex Williamson" <alex.williamson@xxxxxx> wrote:
> >> It has to be handled in top itself. With some versions at least it was the
> >> case that top would crash when CPUs where hot-unplugged. If you revert that
> >> patch, does your version of top work okay in the hot-unplug case (you have
> >> to run top across the unplug operation to see if it will crash or not)?
> > 
> >    Top still crashes without that patch, but the patch just hides the
> > problem.  Top also crashes during a CPU hotplug operation on bare metal.
> > I think this patch causes more problems than if fixes.  Thanks,
> The fact that physical CPU hotplug is an incredibly rare operation, even on
> the 0.001% of all systems that it is actually supported on, compared with
> virtual CPU hotplug being potentially quite frequent, is a real concern.
> Users are actually moderately likely to see this bug when running on Xen. In
> fact they used to, and then they complained to us, at which point we applied
> the band-aid solution.

   Likewise, I've had users complain that the
sysconf(_SC_NPROCESSORS_ONLN) fails to report the correct number of
online CPUs with this patch.  Thanks,


Alex Williamson                             HP Open Source & Linux Org.

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