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Re: [Qemu-devel] [PATCH 2/3] push CPUID level to 4 to allow Intel multic
Re: [Qemu-devel] [PATCH 2/3] push CPUID level to 4 to allow Intel multicore decoding
Thu, 20 Aug 2009 23:35:07 +0200
Thunderbird 126.96.36.199 (X11/20081105)
Jamie Lokier wrote:
Well, but long enough to get those software issues ruled out. If any
serious OS would have had problems, somebody would have noticed and
Andre Przywara wrote:
The other option would be to push the level only to four if we use more
than one thread or core.
In my research it turned out that Intel pushed the level beyond 4
with Pentium4 Prescott (probably with the introduction of real dual
core chips to differentiate threads and cores), so this is quite
some time ago.
Pentium 4 wasn't that long ago, from a point of view of running legacy
Yeah, but most of the stuff Linux checks are bugs and workarounds, so I
am not 100% sure whether it's an advantage. We should be careful with
adjusting the working default QEMU/KVM has right now.
I see quite a lot of code in Linux (to pick an example - presumably
also other OSes) which checks for things by looking at model and
family number, so I wonder if it's wise to depart a long way from
CPUIDs which resemble real hardware which has existed.
We've already seen a problem along these lines, which was the x86
CPUID_SEP feature not getting used properly, but that was quite well
hidden, only affecting one application (Skype) on Windows.
Could it make more sense to, in effect, upgrade the default CPUID
to Pentium 4 (instead of Pentium Pro) when cores > 1?
OK, OK, I will finally send this patch out (following in another mail).
This is a kvm64 CPU (which should become the new KVM's default, if it
proves to work well). It looks like a P4 Prescott, that seems to be a
good base, since it has a decent base line of features and is among the
first CPUs which are supported by KVM.
If someone has such a real beast (best would be a Pentium 4 662 or other
Prescotts with x86_64, HT and VT-x), I would love to see a complete
CPUID dump (including the 0000_0004 subleafs, which x86info omits).
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[Qemu-devel] [PATCH 1/3] extend -smp parsing to include cores= and threads= options, Andre Przywara, 2009/08/19
[Qemu-devel] [PATCH 3/3] set CPUID bits to present cores and threads topology, Andre Przywara, 2009/08/19