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Date: Fri, 11 Aug 2017 08:51:14 -0300
From: Eduardo Habkost <ehabkost@redhat.com>
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Subject: Re: [Qemu-devel] [PATCH] x86: Increase max vcpu number to 352
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To: Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>
Cc: Lan Tianyu <tianyu.lan@intel.com>, qemu-devel@nongnu.org, pbonzini@redhat.com, rth@twiddle.net, mst@redhat.com

On Thu, Aug 10, 2017 at 02:08:38PM -0400, Konrad Rzeszutek Wilk wrote:
> On Wed, Aug 09, 2017 at 11:58:20PM -0400, Lan Tianyu wrote:
> > Intel Xeon phi chip will support 352 logical threads. For HPC
> > usage case, it will create a huge VM with vcpus number as same as host
> > cpus. This patch is to increase max vcpu number to 352.
> 
> There is this ioctl called KVM_CAP_MAX_VCPUS. Why not use that?
> 
> Oh wait, this is generic code. Perhaps there is a way to make
> this more abstract? Where this information is provided via
> an function to which various accelerators register?

We already check KVM_CAP_MAX_VCPUS, see kvm-all.c:kvm_init().
MachineClass::max_cpus is a limit defined at compile time, based
on the limitations of the existing QEMU machine/device code.

-- 
Eduardo