From: "Michael S. Tsirkin" <mst@redhat.com>
To: Jason Wang <jasowang@redhat.com>
Cc: kvm@vger.kernel.org, netdev@vger.kernel.org,
linux-kernel@vger.kernel.org,
virtualization@lists.linux-foundation.org,
linux-api@vger.kernel.org
Subject: Re: [PATCH net-next RFC 1/3] virtio: support for urgent descriptors
Date: Mon, 13 Oct 2014 10:16:19 +0300 [thread overview]
Message-ID: <20141013071619.GA10178@redhat.com> (raw)
In-Reply-To: <543B6F94.2090107@redhat.com>
On Mon, Oct 13, 2014 at 02:22:12PM +0800, Jason Wang wrote:
> On 10/12/2014 05:27 PM, Michael S. Tsirkin wrote:
> > On Sat, Oct 11, 2014 at 03:16:44PM +0800, Jason Wang wrote:
> >> Below should be useful for some experiments Jason is doing.
> >> I thought I'd send it out for early review/feedback.
> >>
> >> event idx feature allows us to defer interrupts until
> >> a specific # of descriptors were used.
> >> Sometimes it might be useful to get an interrupt after
> >> a specific descriptor, regardless.
> >> This adds a descriptor flag for this, and an API
> >> to create an urgent output descriptor.
> >> This is still an RFC:
> >> we'll need a feature bit for drivers to detect this,
> >> but we've run out of feature bits for virtio 0.X.
> >> For experimentation purposes, drivers can assume
> >> this is set, or add a driver-specific feature bit.
> >>
> >> Signed-off-by: Michael S. Tsirkin <mst@redhat.com>
> >> Signed-off-by: Jason Wang <jasowang@redhat.com>
> > I see that as compared to my original patch, you have
> > added a new flag: VRING_AVAIL_F_NO_URGENT_INTERRUPT
> > I don't think it's necessary, see below.
> >
> > As such, I think this patch should be split:
> > - original patch adding support for urgent descriptors
> > - a patch adding virtqueue_enable/disable_cb_urgent(_prepare)?
>
> Not sure this is a good idea, since the api of first patch is in-completed.
> >
> >> ---
> >> drivers/virtio/virtio_ring.c | 75 +++++++++++++++++++++++++++++++++++++---
> >> include/linux/virtio.h | 14 ++++++++
> >> include/uapi/linux/virtio_ring.h | 5 ++-
> >> 3 files changed, 89 insertions(+), 5 deletions(-)
> >>
> [...]
> >>
> >> +unsigned virtqueue_enable_cb_prepare_urgent(struct virtqueue *_vq)
> >> +{
> >> + struct vring_virtqueue *vq = to_vvq(_vq);
> >> + u16 last_used_idx;
> >> +
> >> + START_USE(vq);
> >> + vq->vring.avail->flags &= ~VRING_AVAIL_F_NO_URGENT_INTERRUPT;
> >> + last_used_idx = vq->last_used_idx;
> >> + END_USE(vq);
> >> + return last_used_idx;
> >> +}
> >> +EXPORT_SYMBOL_GPL(virtqueue_enable_cb_prepare_urgent);
> >> +
> > You can implement virtqueue_enable_cb_prepare_urgent
> > simply by clearing ~VRING_AVAIL_F_NO_INTERRUPT.
> >
> > The effect is same: host sends interrupts only if there
> > is an urgent descriptor.
>
> Seems not, consider the case when event index was disabled. This will
> turn on all interrupts.
This means that a legacy device without event index support
will get more interrupts.
Sounds reasonable.
--
MST
next prev parent reply other threads:[~2014-10-13 7:16 UTC|newest]
Thread overview: 18+ messages / expand[flat|nested] mbox.gz Atom feed top
2014-10-11 7:16 [PATCH net-next RFC 0/3] virtio-net: Conditionally enable tx interrupt Jason Wang
2014-10-11 7:16 ` [PATCH net-next RFC 1/3] virtio: support for urgent descriptors Jason Wang
2014-10-12 9:27 ` Michael S. Tsirkin
2014-10-13 6:22 ` Jason Wang
2014-10-13 7:16 ` Michael S. Tsirkin [this message]
2014-10-15 5:40 ` Rusty Russell
2014-10-17 5:23 ` Jason Wang
2014-10-11 7:16 ` [PATCH net-next RFC 2/3] vhost: support " Jason Wang
2014-10-11 7:16 ` [PATCH net-next RFC 3/3] virtio-net: conditionally enable tx interrupt Jason Wang
2014-10-11 14:48 ` Eric Dumazet
2014-10-13 6:02 ` Jason Wang
2014-10-14 21:51 ` Michael S. Tsirkin
2014-10-15 3:34 ` Jason Wang
[not found] ` <1413011806-3813-1-git-send-email-jasowang-H+wXaHxf7aLQT0dZR+AlfA@public.gmane.org>
2014-10-14 18:53 ` [PATCH net-next RFC 0/3] virtio-net: Conditionally " David Miller
2014-10-14 21:51 ` Michael S. Tsirkin
2014-10-15 3:24 ` Jason Wang
2014-10-14 23:06 ` Michael S. Tsirkin
2014-10-15 7:28 ` Jason Wang
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