Date: Sun, 7 Apr 2013 11:43:01 +0300
From: "Michael S. Tsirkin" <mst@redhat.com>
To: Gleb Natapov <gleb@redhat.com>
Cc: Alexander Graf <agraf@suse.de>, Marcelo Tosatti <mtosatti@redhat.com>,
        Thomas Gleixner <tglx@linutronix.de>, Ingo Molnar <mingo@redhat.com>,
        "H. Peter Anvin" <hpa@zytor.com>, x86@kernel.org,
        Xiao Guangrong <xiaoguangrong@linux.vnet.ibm.com>,
        Takuya Yoshikawa <yoshikawa_takuya_b1@lab.ntt.co.jp>,
        Alex Williamson <alex.williamson@redhat.com>,
        Will Deacon <will.deacon@arm.com>,
        Christoffer Dall <c.dall@virtualopensystems.com>,
        Sasha Levin <sasha.levin@oracle.com>,
        Andrew Morton <akpm@linux-foundation.org>, kvm@vger.kernel.org,
        linux-kernel@vger.kernel.org,
        virtualization@lists.linux-foundation.org
Subject: Re: [PATCH RFC] kvm: add PV MMIO EVENTFD
Message-ID: <20130407084301.GC10317@redhat.com>
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 <20130404125649.GI17919@redhat.com>
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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
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