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Date: Wed, 20 Jun 2018 17:29:11 +0300
From: "Michael S. Tsirkin" <mst@redhat.com>
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Subject: Re: [Qemu-devel] [PATCH v3 1/2] kvm: support -dedicated
 cpu-pm=on|off
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To: Paolo Bonzini <pbonzini@redhat.com>
Cc: qemu-devel@nongnu.org, Richard Henderson <rth@twiddle.net>, Eduardo Habkost <ehabkost@redhat.com>, Marcelo Tosatti <mtosatti@redhat.com>, kvm@vger.kernel.org

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 ...

> 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. 

> 
> Paolo

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.

Or, how about

-locked

?


> > The issues in question:
> > 1. a malicious guest can cause high latency for others sharing the host cpu.
> > 2. to host scheduler cpu looks busier than it really is.