From mboxrd@z Thu Jan 1 00:00:00 1970 From: "Michael S. Tsirkin" Subject: Re: [PATCH net-next RFC 1/3] virtio: support for urgent descriptors Date: Mon, 13 Oct 2014 10:16:19 +0300 Message-ID: <20141013071619.GA10178@redhat.com> References: <1413011806-3813-1-git-send-email-jasowang@redhat.com> <1413011806-3813-2-git-send-email-jasowang@redhat.com> <20141012092744.GA9567@redhat.com> <543B6F94.2090107@redhat.com> Mime-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Return-path: Content-Disposition: inline In-Reply-To: <543B6F94.2090107@redhat.com> List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Sender: virtualization-bounces@lists.linux-foundation.org Errors-To: virtualization-bounces@lists.linux-foundation.org To: Jason Wang Cc: kvm@vger.kernel.org, netdev@vger.kernel.org, linux-kernel@vger.kernel.org, virtualization@lists.linux-foundation.org, linux-api@vger.kernel.org List-Id: linux-api@vger.kernel.org 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 > >> Signed-off-by: Jason Wang > > 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