From: Avi Kivity <avi@redhat.com>
To: Stefan Hajnoczi <stefanha@gmail.com>
Cc: Christoph Hellwig <hch@infradead.org>,
Stefan Hajnoczi <stefanha@linux.vnet.ibm.com>,
qemu-devel@nongnu.org, kvm@vger.kernel.org,
"Michael S. Tsirkin" <mst@redhat.com>,
Khoa Huynh <khoa@us.ibm.com>
Subject: Re: [Qemu-devel] Re: [PATCH 2/3] virtio-pci: Use ioeventfd for virtqueue notify
Date: Mon, 06 Dec 2010 17:09:24 +0200 [thread overview]
Message-ID: <4CFCFCA4.3050805@redhat.com> (raw)
In-Reply-To: <AANLkTik7h_4ywLuq2rf+6ZHts18rACNdMMWgrSg-owcs@mail.gmail.com>
On 12/01/2010 11:34 PM, Stefan Hajnoczi wrote:
> >> The guest CPU utilization numbers include an efficiency metric: %vcpu
> >> per MB/sec. Here we see significant improvements too. Guests that
> >> previously couldn't get more CPU work done now have regained some
> >> breathing space.
> >
> > Thanks for those numbers. The guest improvements were expected, but the
> > host numbers surprised me. Do you have an explanation as to why total host
> > load should decrease?
>
> The first vcpu does virtqueue kick - it holds the guest driver
> vblk->lock across kick. Before this kick completes a second vcpu
> tries to acquire vblk->lock, finds it is contended, and spins. So
> we're burning CPU due to the long vblk->lock hold times.
>
> With virtio-ioeventfd those kick times are reduced an there is less
> contention on vblk->lock.
Makes sense.
--
error compiling committee.c: too many arguments to function
next prev parent reply other threads:[~2010-12-06 15:10 UTC|newest]
Thread overview: 23+ messages / expand[flat|nested] mbox.gz Atom feed top
2010-11-11 13:47 [PATCH v2 0/3] virtio: Use ioeventfd for virtqueue notify Stefan Hajnoczi
2010-11-11 13:47 ` [PATCH 1/3] virtio-pci: Rename bugs field to flags Stefan Hajnoczi
2010-11-11 13:47 ` [PATCH 2/3] virtio-pci: Use ioeventfd for virtqueue notify Stefan Hajnoczi
2010-11-11 15:53 ` Michael S. Tsirkin
2010-11-12 9:18 ` Stefan Hajnoczi
2010-11-12 9:25 ` Michael S. Tsirkin
2010-11-12 13:10 ` Stefan Hajnoczi
2010-11-11 16:45 ` Christoph Hellwig
2010-11-12 9:20 ` [Qemu-devel] " Stefan Hajnoczi
2010-11-14 10:34 ` Avi Kivity
2010-11-14 10:37 ` Stefan Hajnoczi
2010-11-14 11:05 ` Avi Kivity
2010-11-14 12:19 ` Avi Kivity
2010-11-15 11:20 ` Stefan Hajnoczi
2010-12-01 11:44 ` Stefan Hajnoczi
2010-12-01 12:30 ` Avi Kivity
2010-12-01 21:34 ` Stefan Hajnoczi
2010-12-06 15:09 ` Avi Kivity [this message]
2010-11-11 16:59 ` Avi Kivity
2010-11-11 17:12 ` Michael S. Tsirkin
2010-11-11 17:55 ` Gleb Natapov
2010-11-11 13:47 ` [PATCH 3/3] virtio-pci: Don't use ioeventfd on old kernels Stefan Hajnoczi
2010-11-11 17:46 ` [PATCH v2 0/3] virtio: Use ioeventfd for virtqueue notify Michael S. Tsirkin
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