Re: [RFC] allow multi-core guests: introduce cores= option to -cpu

From: Alexander Graf <agraf@suse.de>
To: Avi Kivity <avi@redhat.com>
Cc: Andre Przywara <andre.przywara@amd.com>,
	anthony@codemonkey.ws, qemu-devel@nongnu.org,
	kvm@vger.kernel.org
Subject: Re: [RFC] allow multi-core guests: introduce cores= option to -cpu
Date: Sun, 5 Jul 2009 15:23:27 +0200	[thread overview]
Message-ID: <DB13E24C-654D-4752-884E-D951A42D4CB5@suse.de> (raw)
In-Reply-To: <4A4F745C.8010001@redhat.com>

On 04.07.2009, at 17:25, Avi Kivity wrote:

> On 07/03/2009 05:41 PM, Andre Przywara wrote:
>> Hi,
>>
>> currently SMP guests happen to see<n>  vCPUs as<n>  different  
>> sockets.
>> Some guests (Windows comes to mind) have license restrictions and  
>> refuse
>> to run on multi-socket machines.
>> So lets introduce a "cores=" parameter to the -cpu option to let  
>> the user
>> specify the number of _cores_ the guest should see.
>>
>> This patch has not been tested with all corner cases, so I just  
>> want to
>> hear your comments whether
>> a) we need such an option  and
>> b) you like this particular approach.
>>
>> Applying this qemu.git patch to qemu-kvm.git fixes Windows SMP boot  
>> on
>> some versions, I successfully tried up to -smp 16 -cpu host,cores=8  
>> with
>> WindowsXP Pro.
>>
>>
>
> I thought of using -smp [processors=]2,cores=4,threads=2 (for a  
> total of 16 threads), but I think it makes more sense with -cpu.

I actually think putting this in -smp makes more sense. -cpu really  
shouldn't need to be touched by normal users and as long as you can  
either -cpu host or -cpu safe that should be enough.

But then again maybe we should replace -smp with something more useful  
like -numa where you'd then specify #CPUs, #cores, mem-cpu connection,  
etc.

Alex