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

To: Alex Williamson <alex.williamson@xxxxxx>
Subject: Re: [Xen-devel] Is patches/linux-2.6.18/xen-hotplug.patch still necessary?
From: Keir Fraser <keir@xxxxxxxxxxxxx>
Date: Wed, 09 May 2007 16:32:29 +0100
Cc: xen-devel <xen-devel@xxxxxxxxxxxxxxxxxxx>
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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.

 -- Keir

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