From mboxrd@z Thu Jan 1 00:00:00 1970 From: Jason Wang Subject: Re: [PATCH net-next RFC 1/3] virtio: support for urgent descriptors Date: Mon, 13 Oct 2014 14:22:12 +0800 Message-ID: <543B6F94.2090107@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> Mime-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Cc: kvm@vger.kernel.org, netdev@vger.kernel.org, linux-kernel@vger.kernel.org, virtualization@lists.linux-foundation.org, linux-api@vger.kernel.org To: "Michael S. Tsirkin" Return-path: In-Reply-To: <20141012092744.GA9567@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 List-Id: netdev.vger.kernel.org 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.