From mboxrd@z Thu Jan 1 00:00:00 1970 From: Jason Wang Subject: Re: [RFC PATCH net-next 2/6] virtio: introduce virtio_enable_cb_avail() Date: Wed, 15 Oct 2014 18:19:15 +0800 Message-ID: <543E4A23.7060903@redhat.com> References: <1413357930-45302-1-git-send-email-jasowang@redhat.com> <1413357930-45302-3-git-send-email-jasowang@redhat.com> <20141015092849.GA25776@redhat.com> Mime-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Cc: eric.dumazet@gmail.com, netdev@vger.kernel.org, linux-kernel@vger.kernel.org, virtualization@lists.linux-foundation.org, davem@davemloft.net To: "Michael S. Tsirkin" Return-path: In-Reply-To: <20141015092849.GA25776@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 10/15/2014 05:28 PM, Michael S. Tsirkin wrote: > On Wed, Oct 15, 2014 at 03:25:26PM +0800, Jason Wang wrote: >> This patch introduces virtio_enable_cb_avail() to publish avail idx >> and used event. This could be used by batched buffer submitting to >> reduce the number of tx interrupts. >> >> Cc: Rusty Russell >> Cc: Michael S. Tsirkin >> Signed-off-by: Jason Wang >> --- >> drivers/virtio/virtio_ring.c | 22 ++++++++++++++++++++-- >> include/linux/virtio.h | 2 ++ >> 2 files changed, 22 insertions(+), 2 deletions(-) >> >> diff --git a/drivers/virtio/virtio_ring.c b/drivers/virtio/virtio_ring.c >> index 1b3929f..d67fbf8 100644 >> --- a/drivers/virtio/virtio_ring.c >> +++ b/drivers/virtio/virtio_ring.c >> @@ -567,14 +567,32 @@ unsigned virtqueue_enable_cb_prepare(struct virtqueue *_vq) >> * entry. Always do both to keep code simple. */ >> vq->vring.avail->flags &= ~VRING_AVAIL_F_NO_INTERRUPT; >> /* Make sure used event never go backwards */ >> - if (!vring_need_event(vring_used_event(&vq->vring), >> - vq->vring.avail->idx, last_used_idx)) >> + if (vq->vring.avail->idx != vring_used_event(&vq->vring) && >> + !vring_need_event(vring_used_event(&vq->vring), >> + vq->vring.avail->idx, last_used_idx)) { >> vring_used_event(&vq->vring) = last_used_idx; >> + } >> END_USE(vq); >> return last_used_idx; >> } >> EXPORT_SYMBOL_GPL(virtqueue_enable_cb_prepare); >> > I see you are also changing virtqueue_enable_cb_prepare, why? This is also used to prevent it from moving the used event backwards. This may happens when we handle tx napi after we publish avail idx as used event (virtqueue_enable_cb_avail() was called). > >> +bool virtqueue_enable_cb_avail(struct virtqueue *_vq) >> +{ >> + struct vring_virtqueue *vq = to_vvq(_vq); >> + bool ret; >> + >> + START_USE(vq); >> + vq->vring.avail->flags &= ~VRING_AVAIL_F_NO_INTERRUPT; >> + vring_used_event(&vq->vring) = vq->vring.avail->idx; >> + ret = vring_need_event(vq->vring.avail->idx, >> + vq->last_used_idx, vq->vring.used->idx); >> + END_USE(vq); >> + >> + return ret; >> +} >> +EXPORT_SYMBOL_GPL(virtqueue_enable_cb_avail); >> + >> /** >> * virtqueue_poll - query pending used buffers >> * @vq: the struct virtqueue we're talking about. > Could not figure out what this does. > Please add documentation. > Sure, does something like below explain what does this function do? /** * virtqueue_enable_cb_avail - restart callbacks after disable_cb. * @vq: the struct virtqueue we're talking about. * * This re-enables callbacks but hints to the other side to delay * interrupts all of the available buffers have been processed; * it returns "false" if there are at least one pending buffer in the queue, * to detect a possible race between the driver checking for more work, * and enabling callbacks. * * Caller must ensure we don't call this with other virtqueue * operations at the same time (except where noted). */ >> diff --git a/include/linux/virtio.h b/include/linux/virtio.h >> index b46671e..bfaf058 100644 >> --- a/include/linux/virtio.h >> +++ b/include/linux/virtio.h >> @@ -65,6 +65,8 @@ bool virtqueue_enable_cb(struct virtqueue *vq); >> >> unsigned virtqueue_enable_cb_prepare(struct virtqueue *vq); >> >> +bool virtqueue_enable_cb_avail(struct virtqueue *vq); >> + >> bool virtqueue_poll(struct virtqueue *vq, unsigned); >> >> bool virtqueue_enable_cb_delayed(struct virtqueue *vq); >> -- >> 1.7.1 > -- > To unsubscribe from this list: send the line "unsubscribe linux-kernel" in > the body of a message to majordomo@vger.kernel.org > More majordomo info at http://vger.kernel.org/majordomo-info.html > Please read the FAQ at http://www.tux.org/lkml/