linux-kernel - [PATCH] virtio_ring: remove unnecessary to

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Message-Id: <20220324073340.632656-1-xianting.tian@linux.alibaba.com>
Date:   Thu, 24 Mar 2022 15:33:40 +0800
From:   Xianting Tian <xianting.tian@...ux.alibaba.com>
To:     mst@...hat.com, jasowang@...hat.com
Cc:     virtualization@...ts.linux-foundation.org,
        linux-kernel@...r.kernel.org,
        Xianting Tian <xianting.tian@...ux.alibaba.com>
Subject: [PATCH] virtio_ring: remove unnecessary to_vvq call in vring hot path

It passes '_vq' to virtqueue_use_indirect(), which still calls
to_vvq to get 'vq', let's directly pass 'vq'. It can avoid
unnecessary call of to_vvq in hot path.

Other tiny optimization:
Add unlikely to "if (vq->vq.num_free < descs_used).

Signed-off-by: Xianting Tian <xianting.tian@...ux.alibaba.com>
---
 drivers/virtio/virtio_ring.c | 10 ++++------
 1 file changed, 4 insertions(+), 6 deletions(-)

diff --git a/drivers/virtio/virtio_ring.c b/drivers/virtio/virtio_ring.c
index 962f1477b1fa..ab6d5f0cb579 100644
--- a/drivers/virtio/virtio_ring.c
+++ b/drivers/virtio/virtio_ring.c
@@ -205,11 +205,9 @@ struct vring_virtqueue {
 
 #define to_vvq(_vq) container_of(_vq, struct vring_virtqueue, vq)
 
-static inline bool virtqueue_use_indirect(struct virtqueue *_vq,
+static inline bool virtqueue_use_indirect(struct vring_virtqueue *vq,
 					  unsigned int total_sg)
 {
-	struct vring_virtqueue *vq = to_vvq(_vq);
-
 	/*
 	 * If the host supports indirect descriptor tables, and we have multiple
 	 * buffers, then go indirect. FIXME: tune this threshold
@@ -507,7 +505,7 @@ static inline int virtqueue_add_split(struct virtqueue *_vq,
 
 	head = vq->free_head;
 
-	if (virtqueue_use_indirect(_vq, total_sg))
+	if (virtqueue_use_indirect(vq, total_sg))
 		desc = alloc_indirect_split(_vq, total_sg, gfp);
 	else {
 		desc = NULL;
@@ -527,7 +525,7 @@ static inline int virtqueue_add_split(struct virtqueue *_vq,
 		descs_used = total_sg;
 	}
 
-	if (vq->vq.num_free < descs_used) {
+	if (unlikely(vq->vq.num_free < descs_used)) {
 		pr_debug("Can't add buf len %i - avail = %i\n",
 			 descs_used, vq->vq.num_free);
 		/* FIXME: for historical reasons, we force a notify here if
@@ -1194,7 +1192,7 @@ static inline int virtqueue_add_packed(struct virtqueue *_vq,
 
 	BUG_ON(total_sg == 0);
 
-	if (virtqueue_use_indirect(_vq, total_sg)) {
+	if (virtqueue_use_indirect(vq, total_sg)) {
 		err = virtqueue_add_indirect_packed(vq, sgs, total_sg, out_sgs,
 						    in_sgs, data, gfp);
 		if (err != -ENOMEM) {
-- 
2.17.1