From mboxrd@z Thu Jan 1 00:00:00 1970 From: Jason Wang Subject: Re: [PATCH 1/2] virtio: support unlocked queue poll Date: Tue, 09 Jul 2013 11:26:49 +0800 Message-ID: <51DB82F9.7070307@redhat.com> References: <1373274069-4301-1-git-send-email-mst@redhat.com> <1373274069-4301-2-git-send-email-mst@redhat.com> Mime-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Cc: netdev@vger.kernel.org, linux-kernel@vger.kernel.org, virtualization@lists.linux-foundation.org To: "Michael S. Tsirkin" Return-path: In-Reply-To: <1373274069-4301-2-git-send-email-mst@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 07/08/2013 05:04 PM, Michael S. Tsirkin wrote: > This adds a way to check ring empty state after enable_cb outside any > locks. Will be used by virtio_net. > > Note: there's room for more optimization: caller is likely to have a > memory barrier already, which means we might be able to get rid of a > barrier here. Deferring this optimization until we do some > benchmarking. > > Signed-off-by: Michael S. Tsirkin > --- Tested-by: Jason Wang Acked-by: Jason Wang > drivers/virtio/virtio_ring.c | 56 ++++++++++++++++++++++++++++++++++---------- > include/linux/virtio.h | 4 ++++ > 2 files changed, 48 insertions(+), 12 deletions(-) > > diff --git a/drivers/virtio/virtio_ring.c b/drivers/virtio/virtio_ring.c > index 5217baf..37d58f8 100644 > --- a/drivers/virtio/virtio_ring.c > +++ b/drivers/virtio/virtio_ring.c > @@ -607,19 +607,21 @@ void virtqueue_disable_cb(struct virtqueue *_vq) > EXPORT_SYMBOL_GPL(virtqueue_disable_cb); > > /** > - * virtqueue_enable_cb - restart callbacks after disable_cb. > + * virtqueue_enable_cb_prepare - restart callbacks after disable_cb > * @vq: the struct virtqueue we're talking about. > * > - * This re-enables callbacks; it returns "false" if there are pending > - * buffers in the queue, to detect a possible race between the driver > - * checking for more work, and enabling callbacks. > + * This re-enables callbacks; it returns current queue state > + * in an opaque unsigned value. This value should be later tested by > + * virtqueue_poll, 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). > */ > -bool virtqueue_enable_cb(struct virtqueue *_vq) > +unsigned virtqueue_enable_cb_prepare(struct virtqueue *_vq) > { > struct vring_virtqueue *vq = to_vvq(_vq); > + u16 last_used_idx; > > START_USE(vq); > > @@ -629,15 +631,45 @@ bool virtqueue_enable_cb(struct virtqueue *_vq) > * either clear the flags bit or point the event index at the next > * entry. Always do both to keep code simple. */ > vq->vring.avail->flags &= ~VRING_AVAIL_F_NO_INTERRUPT; > - vring_used_event(&vq->vring) = vq->last_used_idx; > + vring_used_event(&vq->vring) = last_used_idx = vq->last_used_idx; > + END_USE(vq); > + return last_used_idx; > +} > +EXPORT_SYMBOL_GPL(virtqueue_enable_cb_prepare); > + > +/** > + * virtqueue_poll - query pending used buffers > + * @vq: the struct virtqueue we're talking about. > + * @last_used_idx: virtqueue state (from call to virtqueue_enable_cb_prepare). > + * > + * Returns "true" if there are pending used buffers in the queue. > + * > + * This does not need to be serialized. > + */ > +bool virtqueue_poll(struct virtqueue *_vq, unsigned last_used_idx) > +{ > + struct vring_virtqueue *vq = to_vvq(_vq); > + > virtio_mb(vq->weak_barriers); > - if (unlikely(more_used(vq))) { > - END_USE(vq); > - return false; > - } > + return (u16)last_used_idx != vq->vring.used->idx; > +} > +EXPORT_SYMBOL_GPL(virtqueue_poll); > > - END_USE(vq); > - return true; > +/** > + * virtqueue_enable_cb - restart callbacks after disable_cb. > + * @vq: the struct virtqueue we're talking about. > + * > + * This re-enables callbacks; it returns "false" if there are pending > + * buffers 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). > + */ > +bool virtqueue_enable_cb(struct virtqueue *_vq) > +{ > + unsigned last_used_idx = virtqueue_enable_cb_prepare(_vq); > + return !virtqueue_poll(_vq, last_used_idx); > } > EXPORT_SYMBOL_GPL(virtqueue_enable_cb); > > diff --git a/include/linux/virtio.h b/include/linux/virtio.h > index 9ff8645..72398ee 100644 > --- a/include/linux/virtio.h > +++ b/include/linux/virtio.h > @@ -70,6 +70,10 @@ void virtqueue_disable_cb(struct virtqueue *vq); > > bool virtqueue_enable_cb(struct virtqueue *vq); > > +unsigned virtqueue_enable_cb_prepare(struct virtqueue *vq); > + > +bool virtqueue_poll(struct virtqueue *vq, unsigned); > + > bool virtqueue_enable_cb_delayed(struct virtqueue *vq); > > void *virtqueue_detach_unused_buf(struct virtqueue *vq);