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Re: [Qemu-devel] [PATCH V2 03/11] virito: introduce bus specific queue l
From: |
Cornelia Huck |
Subject: |
Re: [Qemu-devel] [PATCH V2 03/11] virito: introduce bus specific queue limit |
Date: |
Fri, 27 Feb 2015 10:34:05 +0100 |
On Fri, 27 Feb 2015 03:42:00 +0008
Jason Wang <address@hidden> wrote:
> On Thu, Feb 26, 2015 at 8:57 PM, Cornelia Huck
> <address@hidden> wrote:
> > On Thu, 26 Feb 2015 15:04:38 +0800
> > Jason Wang <address@hidden> wrote:
> >
> >> This patch introduces a bus specific queue limitation. It will be
> >> useful for increasing the limit for one of the bus without
> >> disturbing
> >> other buses.
> >> diff --git a/hw/virtio/virtio.c b/hw/virtio/virtio.c
> >> index ffc22e8..5a806b5 100644
> >> --- a/hw/virtio/virtio.c
> >> +++ b/hw/virtio/virtio.c
> >> @@ -541,6 +541,14 @@ void virtio_update_irq(VirtIODevice *vdev)
> >> virtio_notify_vector(vdev, VIRTIO_NO_VECTOR);
> >> }
> >>
> >> +int virtio_get_queue_max(VirtIODevice *vdev)
> >> +{
> >> + BusState *qbus = qdev_get_parent_bus(DEVICE(vdev));
> >> + VirtioBusClass *k = VIRTIO_BUS_GET_CLASS(qbus);
> >> +
> >> + return k->queue_max;
> >> +}
> >> +
> >
> > Are all callers of this in the slow path? So we don't introduce
> > processing overhead.
>
> Looks not. For overhead, do you mean one introduced by
> VIRTIO_BUS_GET_CLASS()? Not sure how much it will affact but we've
> already used something like this in the datapath, e.g
> virtio_notify_vector().
I may have misremembered how much overhead those types of operation
introduce.
But it made me think: This function is basically introducing a
per-VirtIODevice queue limit. We set it once in the VirtioBusClass
during initialization, but don't expect it to change. Why don't we just
propagate it to a new member of VirtIODevice during initialization
instead?
[Qemu-devel] [PATCH V2 05/11] virtio-serial-bus: switch to bus specific queue limit, Jason Wang, 2015/02/26
[Qemu-devel] [PATCH V2 04/11] virtio-ccw: introduce ccw specific queue limit, Jason Wang, 2015/02/26
[Qemu-devel] [PATCH V2 07/11] virtio-mmio: switch to bus specific queue limit, Jason Wang, 2015/02/26
[Qemu-devel] [PATCH V2 06/11] virtio-s390: switch to bus specific queue limit, Jason Wang, 2015/02/26