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Re: [Qemu-devel] [PATCH v5 2/4] virtio-pci: Use ioeventfd for virtqueue
From: |
Michael S. Tsirkin |
Subject: |
Re: [Qemu-devel] [PATCH v5 2/4] virtio-pci: Use ioeventfd for virtqueue notify |
Date: |
Mon, 24 Jan 2011 21:47:29 +0200 |
User-agent: |
Mutt/1.5.21 (2010-09-15) |
On Mon, Jan 24, 2011 at 08:48:05PM +0100, Kevin Wolf wrote:
> Am 24.01.2011 20:36, schrieb Michael S. Tsirkin:
> > On Mon, Jan 24, 2011 at 07:54:20PM +0100, Kevin Wolf wrote:
> >> Am 12.12.2010 16:02, schrieb Stefan Hajnoczi:
> >>> Virtqueue notify is currently handled synchronously in userspace virtio.
> >>> This
> >>> prevents the vcpu from executing guest code while hardware emulation code
> >>> handles the notify.
> >>>
> >>> On systems that support KVM, the ioeventfd mechanism can be used to make
> >>> virtqueue notify a lightweight exit by deferring hardware emulation to the
> >>> iothread and allowing the VM to continue execution. This model is
> >>> similar to
> >>> how vhost receives virtqueue notifies.
> >>>
> >>> The result of this change is improved performance for userspace virtio
> >>> devices.
> >>> Virtio-blk throughput increases especially for multithreaded scenarios and
> >>> virtio-net transmit throughput increases substantially.
> >>>
> >>> Some virtio devices are known to have guest drivers which expect a notify
> >>> to be
> >>> processed synchronously and spin waiting for completion. Only enable
> >>> ioeventfd
> >>> for virtio-blk and virtio-net for now.
> >>>
> >>> Care must be taken not to interfere with vhost-net, which uses host
> >>> notifiers. If the set_host_notifier() API is used by a device
> >>> virtio-pci will disable virtio-ioeventfd and let the device deal with
> >>> host notifiers as it wishes.
> >>>
> >>> After migration and on VM change state (running/paused) virtio-ioeventfd
> >>> will enable/disable itself.
> >>>
> >>> * VIRTIO_CONFIG_S_DRIVER_OK -> enable virtio-ioeventfd
> >>> * !VIRTIO_CONFIG_S_DRIVER_OK -> disable virtio-ioeventfd
> >>> * virtio_pci_set_host_notifier() -> disable virtio-ioeventfd
> >>> * vm_change_state(running=0) -> disable virtio-ioeventfd
> >>> * vm_change_state(running=1) -> enable virtio-ioeventfd
> >>>
> >>> Signed-off-by: Stefan Hajnoczi <address@hidden>
> >>
> >> On current git master I'm getting hangs when running iozone on a
> >> virtio-blk disk. "Hang" means that it's not responsive any more and has
> >> 100% CPU consumption.
> >>
> >> I bisected the problem to this patch. Any ideas?
> >>
> >> Kevin
> >
> > Does it help if you set ioeventfd=off on command line?
>
> Yes, with ioeventfd=off it seems to work fine.
>
> Kevin
Then it's the ioeventfd that is to blame.
Is it the io thread that consumes 100% CPU?
Or the vcpu thread?
--
MST
- Re: [Qemu-devel] [PATCH v5 2/4] virtio-pci: Use ioeventfd for virtqueue notify, Kevin Wolf, 2011/01/24
- Re: [Qemu-devel] [PATCH v5 2/4] virtio-pci: Use ioeventfd for virtqueue notify, Michael S. Tsirkin, 2011/01/24
- Re: [Qemu-devel] [PATCH v5 2/4] virtio-pci: Use ioeventfd for virtqueue notify, Kevin Wolf, 2011/01/24
- Re: [Qemu-devel] [PATCH v5 2/4] virtio-pci: Use ioeventfd for virtqueue notify,
Michael S. Tsirkin <=
- Re: [Qemu-devel] [PATCH v5 2/4] virtio-pci: Use ioeventfd for virtqueue notify, Kevin Wolf, 2011/01/24
- Re: [Qemu-devel] [PATCH v5 2/4] virtio-pci: Use ioeventfd for virtqueue notify, Stefan Hajnoczi, 2011/01/25
- Re: [Qemu-devel] [PATCH v5 2/4] virtio-pci: Use ioeventfd for virtqueue notify, Stefan Hajnoczi, 2011/01/25
- Re: [Qemu-devel] [PATCH v5 2/4] virtio-pci: Use ioeventfd for virtqueue notify, Stefan Hajnoczi, 2011/01/25
- Re: [Qemu-devel] [PATCH v5 2/4] virtio-pci: Use ioeventfd for virtqueue notify, Michael S. Tsirkin, 2011/01/25
- Re: [Qemu-devel] [PATCH v5 2/4] virtio-pci: Use ioeventfd for virtqueue notify, Stefan Hajnoczi, 2011/01/25
- Re: [Qemu-devel] [PATCH v5 2/4] virtio-pci: Use ioeventfd for virtqueue notify, Stefan Hajnoczi, 2011/01/25
- Re: [Qemu-devel] [PATCH v5 2/4] virtio-pci: Use ioeventfd for virtqueue notify, Anthony Liguori, 2011/01/25
- Re: [Qemu-devel] [PATCH v5 2/4] virtio-pci: Use ioeventfd for virtqueue notify, Stefan Hajnoczi, 2011/01/25
- Re: [Qemu-devel] [PATCH v5 2/4] virtio-pci: Use ioeventfd for virtqueue notify, Anthony Liguori, 2011/01/25