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Date: Wed, 22 Mar 2017 17:54:39 +0100
From: Radim =?utf-8?B?S3LEjW3DocWZ?= <rkrcmar@redhat.com>
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Subject: Re: [Qemu-devel] [PATCH] pc: q35: bump max_cpus to INT32_MAX
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To: "Michael S. Tsirkin" <mst@redhat.com>
Cc: qemu-devel@nongnu.org, Igor Mammedov <imammedo@redhat.com>, Paolo Bonzini <pbonzini@redhat.com>, Richard Henderson <rth@twiddle.net>, Eduardo Habkost <ehabkost@redhat.com>

2017-03-22 18:06+0200, Michael S. Tsirkin:
> On Wed, Mar 22, 2017 at 04:59:06PM +0100, Radim Kr=C4=8Dm=C3=A1=C5=99 w=
rote:
>> QEMU does not allocate based on machine's max_cpus, but only uses it t=
o
>> limit the maximum selected by user and the actual limit of VCPUs is
>> enfoced by other components:
>>  - machine without vIOMMU ends at 255 VCPUs
>>  - TCG currently doesn't support x2APIC, so it also ends below 256
>>  - KVM with vIOMMU cannot exceed the KVM limit (currently 288)
>>=20
>> Using a big value should bring no drawbacks and the benefit is that
>> components (especially out-of-tree KVM) can bump their limits without
>> touching machine's max_cpus.
>>=20
>> max_cpus is unsigned, but it is treated as signed at least in printf a=
nd
>> the other two billion VCPU won't be needed for a while, so we can igno=
re
>> possible bugs by using signed max.
>>=20
>> Signed-off-by: Radim Kr=C4=8Dm=C3=A1=C5=99 <rkrcmar@redhat.com>
>> ---
>>   Should the 2.9 machine type still have 288?
>=20
> It doesn't look like a bugfix to me.
> So if we can defer past 2.9 that would be best IMO.

Sure, I'll wait until the 2.10 machine type pops up.

Thanks.