From 41f0377f73039ca6fe97a469d1941a89cd9757f1 Mon Sep 17 00:00:00 2001 From: Rusty Russell Date: Thu, 12 Jan 2012 15:44:43 +1030 Subject: [PATCH] virtio: support unlocked queue kick Based on patch by Christoph for virtio_blk speedup: Split virtqueue_kick to be able to do the actual notification outside the lock protecting the virtqueue. This patch was originally done by Stefan Hajnoczi, but I can't find the original one anymore and had to recreated it from memory. Pointers to the original or corrections for the commit message are welcome. Stefan's patch was here: https://github.com/stefanha/linux/commit/a6d06644e3a58e57a774e77d7dc34c4a5a2e7496 http://www.spinics.net/lists/linux-virtualization/msg14616.html Third time's the charm! Signed-off-by: Rusty Russell --- drivers/virtio/virtio_ring.c | 60 ++++++++++++++++++++++++++++-------- include/linux/virtio.h | 4 +++ 2 files changed, 52 insertions(+), 12 deletions(-) diff --git a/drivers/virtio/virtio_ring.c b/drivers/virtio/virtio_ring.c index 6ea92a6d113..c56bbe79924 100644 --- a/drivers/virtio/virtio_ring.c +++ b/drivers/virtio/virtio_ring.c @@ -262,19 +262,22 @@ add_head: EXPORT_SYMBOL_GPL(virtqueue_add_buf); /** - * virtqueue_kick - update after add_buf + * virtqueue_kick_prepare - first half of split virtqueue_kick call. * @vq: the struct virtqueue * - * After one or more virtqueue_add_buf calls, invoke this to kick - * the other side. + * Instead of virtqueue_kick(), you can do: + * if (virtqueue_kick_prepare(vq)) + * virtqueue_notify(vq); * - * Caller must ensure we don't call this with other virtqueue - * operations at the same time (except where noted). + * This is sometimes useful because the virtqueue_kick_prepare() needs + * to be serialized, but the actual virtqueue_notify() call does not. */ -void virtqueue_kick(struct virtqueue *_vq) +bool virtqueue_kick_prepare(struct virtqueue *_vq) { struct vring_virtqueue *vq = to_vvq(_vq); u16 new, old; + bool needs_kick; + START_USE(vq); /* Descriptors and available array need to be set before we expose the * new available array entries. */ @@ -287,13 +290,46 @@ void virtqueue_kick(struct virtqueue *_vq) /* Need to update avail index before checking if we should notify */ virtio_mb(vq); - if (vq->event ? - vring_need_event(vring_avail_event(&vq->vring), new, old) : - !(vq->vring.used->flags & VRING_USED_F_NO_NOTIFY)) - /* Prod other side to tell it about changes. */ - vq->notify(&vq->vq); - + if (vq->event) { + needs_kick = vring_need_event(vring_avail_event(&vq->vring), + new, old); + } else { + needs_kick = !(vq->vring.used->flags & VRING_USED_F_NO_NOTIFY); + } END_USE(vq); + return needs_kick; +} +EXPORT_SYMBOL_GPL(virtqueue_kick_prepare); + +/** + * virtqueue_notify - second half of split virtqueue_kick call. + * @vq: the struct virtqueue + * + * This does not need to be serialized. + */ +void virtqueue_notify(struct virtqueue *_vq) +{ + struct vring_virtqueue *vq = to_vvq(_vq); + + /* Prod other side to tell it about changes. */ + vq->notify(_vq); +} +EXPORT_SYMBOL_GPL(virtqueue_notify); + +/** + * virtqueue_kick - update after add_buf + * @vq: the struct virtqueue + * + * After one or more virtqueue_add_buf calls, invoke this to kick + * the other side. + * + * Caller must ensure we don't call this with other virtqueue + * operations at the same time (except where noted). + */ +void virtqueue_kick(struct virtqueue *vq) +{ + if (virtqueue_kick_prepare(vq)) + virtqueue_notify(vq); } EXPORT_SYMBOL_GPL(virtqueue_kick); diff --git a/include/linux/virtio.h b/include/linux/virtio.h index ec1706e7df5..31fe3a62874 100644 --- a/include/linux/virtio.h +++ b/include/linux/virtio.h @@ -34,6 +34,10 @@ int virtqueue_add_buf(struct virtqueue *vq, void virtqueue_kick(struct virtqueue *vq); +bool virtqueue_kick_prepare(struct virtqueue *vq); + +void virtqueue_notify(struct virtqueue *vq); + void *virtqueue_get_buf(struct virtqueue *vq, unsigned int *len); void virtqueue_disable_cb(struct virtqueue *vq); -- 2.20.1