Re: [PATCH RFC] kvm: add PV MMIO EVENTFD

["Michael S. Tsirkin" <mst@redhat.com>]

On Sun, Apr 07, 2013 at 12:30:38PM +0300, Gleb Natapov wrote:
> On Thu, Apr 04, 2013 at 04:14:57PM +0300, Gleb Natapov wrote:
> > > > 
> > > >>> is to move to MMIO only when PIO address space is exhausted. For PCI it
> > > >>> will be never, for PCI-e it will be after ~16 devices.
> > > >> 
> > > >> Ok, let's go back a step here. Are you actually able to measure any speed in performance with this patch applied and without when going through MMIO kicks?
> > > >> 
> > > >> 
> > > > That's the question for MST. I think he did only micro benchmarks till
> > > > now and he already posted his result here:
> > > > 
> > > > mmio-wildcard-eventfd:pci-mem 3529
> > > > mmio-pv-eventfd:pci-mem 1878
> > > > portio-wildcard-eventfd:pci-io 1846
> > > > 
> > > > So the patch speedup mmio by almost 100% and it is almost the same as PIO.
> > > 
> > > Those numbers don't align at all with what I measured.
> > I am trying to run vmexit test on AMD now, but something does not work
> > there. Next week I'll fix it and see how AMD differs, bit on Intel those are the
> > numbers.
> > 
> The numbers are:
> vmcall 1921
> inl_from_kernel 4227
> outl_to_kernel 2345
> 
> outl is specifically optimized to not go through the emulator since it
> is used for virtio kick. mmio-pv-eventfd is the same kind of
> optimization but for mmio.
>  
> --
> 			Gleb.


Hmm so on AMD it's more like 20% overhead, like ARM.

-- 
MST