Re: FPU issue, xm dmesg

[Manuel Bouyer <bouyer%antioche.eu.org@localhost>]

On Wed, Nov 02, 2005 at 12:31:08PM +0100, Quentin Garnier wrote:
> Hi all,
> 
> First, a short notice about port-xen/30977:  it still happens.  Userland
> is from september, everything works fine with a non-Xen kernel, and with
> a Xen kernel, the FPU gets crazy.
> 
> I've tried running benchmarks/paranoia, and sometimes it reports a flaw,
> sometimes it only whines a bit about some rounding, and sometimes it
> says everything is perfect.  With the non-Xen kernel, I always get the
> rounding whining (that makes the fact that paranoia says everything is
> perfect from times to times under Xen even weirder).

Ha, this is interesting. I can reproduce it too with paranoia. I tried a few
other tests but couldn't reproduce the failure.

One though I had about this is that it's possible that the hypervisor uses the
FPU/MMX registers but don't save/restore them. Maybe turning off our lazy FPU
save/restore would fix this ?

> 
> Xen itself is release 2.0.7.  I haven't heard of anyone else having
> those troubles, but obviously I can't really blame a faulty FPU, as it
> doesn't happen with the regular kernel.
> 
> While I'm there, does "xm dmesg" work for anybody?

It doesn't for from linux either for me.

-- 
Manuel Bouyer <bouyer%antioche.eu.org@localhost>
     NetBSD: 26 ans d'experience feront toujours la difference
--