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[Qemu-devel] Re: [RFC] allow multi-core guests: introduce cores= option
[Qemu-devel] Re: [RFC] allow multi-core guests: introduce cores= option to -cpu
Sat, 4 Jul 2009 00:52:30 +0200
Thunderbird 18.104.22.168 (X11/20081105)
Brian Jackson wrote:
Andre Przywara wrote:
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.
Personally, I'd like to see it as an extra arg to the -smp option. We've
seen too many people use -cpu incorrectly in #kvm, so we've gotten into
the habit of telling people not to touch that option unless they know
exactly what they are doing. Plus it seems odd to have to use -cpu foo
when you just want more cpus, not a specific cpu.
Ok, I see your point. I simply used -cpu because of technical reasons
(the core topology is reflected in CPUID, which -cpu cares about). But
you are right, it does not belong here, -smp looks like a good candidate
(IMO better than -numa). Or we use an abstract "-topology" for this, but
this seems like overkill.
So what about: "-smp 4,cores=2,threads=2[,sockets=1]" to inject 4 vCPUs
in one package (automatically determined if omitted) with two cores and
two threads/core? All parameters except the number of vCPUs would be
optional, which would make this new format backwards compatible.
Only we have to agree on the default topology: multi-socket like the
current implementation or multi-core, which would mimic the most common
SMP architecture today. It seems that the latter one causes less
problems for guests.
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