Re: [Qemu-devel] [PATCH v3 1/2] kvm: support -dedicated cpu-pm=on|off

[Paolo Bonzini]

On 20/06/2018 16:29, Michael S. Tsirkin wrote:
> On Wed, Jun 20, 2018 at 04:20:40PM +0200, Paolo Bonzini wrote:
>> On 19/06/2018 22:43, Michael S. Tsirkin wrote:
>>>
>>>> 2) Maybe -hostresource?
>>>
>>> Is ability to cause high latency for other threads really a resource?
>>
>> The "resource" here is host CPU time.
> 
> Right but then everything we do is a host resource in that sense.
> Host network, host disk ...

Yes of course.  These options control how (and how much) QEMU uses those
resources.

>> In general, a vCPU with
>> KVM_CPU_X86_DISABLE_EXITS will use more host CPU time and block
>> overcommitting, just like mlock does for memory.
> 
> What bothers me is that it does not block overcommit as such.
> It has a side effect that if something does end up
> running on the same CPU, that something will get bad
> latency jitter. 
>
> I agree there's similarity here around overcommit.
> 
> That's why I suggested -dedicated as an antonym to -overcommit.
> 
> But I'm fine with -disable-overcommit or -dedicated-host-resource too.

Both of those are quite a mouthful.  I somewhat prefer "-overcommit" to
"-dedicated", though "-hostresource" it's still my favorite mostly
because it's the most future-proof.

Paolo