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From: | Wei Huang |
Subject: | Re: [Qemu-devel] [PATCH 1/1] target-i386: prevent users from setting threads>1 for AMD CPUs |
Date: | Tue, 07 Oct 2014 16:16:51 -0500 |
User-agent: | Mozilla/5.0 (X11; Linux x86_64; rv:24.0) Gecko/20100101 Thunderbird/24.7.0 |
On 10/07/2014 03:58 PM, Paolo Bonzini wrote:
Il 07/10/2014 21:44, Wei Huang ha scritto:AMD CPU doesn't support hyperthreading. Even though QEMU fixes this issue by setting CPUID_0000_0001_EBX and CPUID_8000_0008_ECX via conversion, it is better to stop end-users in the first place with a warning message.Hi Wei, what exactly breaks if you try creating an AMD VM with hyperthreading?
Hi Paolo,It isn't a bug IMO. I tested various combinations; and current QEMU handles it very well. It converts threads=n to proper CPUID_0000_0001_EBX[LogicalProcCount] and CPUID_8000_0008_ECX[NC] accordingly for AMD.
There is a bugzilla reported for such configuration: https://bugzilla.redhat.com/show_bug.cgi?id=1135772. So I thought such checking might be a good thing to do.
I am worried that the default CPU is an AMD one when KVM is disabled, and thus "qemu-system-x86_64 -smp threads=2" will likely be broken.
"-smp threads=2" will be rejected by the patch. Unless the meaning of threads is not limited to threads-per-core, shouldn't end users use "-smp 2" in this case or something like "-smp 2,cores=2,sockets=1"?
Paolo
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