Re: [RFC PATCH V3 0/5] Utilizing VMX preemption for timer virtualization

[yunhong jiang <yunhong.jiang@linux.intel.com>]

On Mon, 6 Jun 2016 14:45:37 +0200
Paolo Bonzini <pbonzini@redhat.com> wrote:

> 
> 
> On 04/06/2016 02:42, Yunhong Jiang wrote:
> > It adds a little bit latency for each VM-entry because we need
> > setup the preemption timer each time.
> 
> Really it doesn't according to your tests:
> 
> > 1. enable_hv_timer=Y.
> > 
> > 000004 002174
> > 000005 042961
> > 000006 479383
> > 000007 071123
> > 000008 003720
> > 
> > 2. enable_hv_timer=N.
> > 
> > # Histogram
> > ......
> > 000005 000042
> > 000006 000772
> > 000007 008262
> > 000008 200759
> > 000009 381126
> > 000010 008056
> 
> So perhaps you can replace that paragraph with "The benefits offset
> the small extra work to do on each VM-entry to setup the preemption
> timer".
> 
> I'll play with this patch and kvm-unit-tests in the next few days.
> 
> David, it would be great if you could also try this on your
> message-passing benchmarks (e.g. TCP_RR).  On one hand they are heavy
> on vmexits, on the other hand they also have many expensive TSC
> deadline WRMSRs.  I have requested a few small changes, but I am very
> happy with the logic and the vmentry cost.
> 
> Thanks,

Paolo, thanks for the feedback a lot. I will get a system with TSC scaling and
try there, and then will update the patch accordingly.

Thanks
--jyh

> 
> Paolo