linux-kernel - [RFC PATCH V3 1/6] vhost: generalize adding used elem

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Message-Id: <20190423055420.26408-2-jasowang@redhat.com>
Date:   Tue, 23 Apr 2019 01:54:15 -0400
From:   Jason Wang <jasowang@...hat.com>
To:     mst@...hat.com, jasowang@...hat.com, kvm@...r.kernel.org,
        virtualization@...ts.linux-foundation.org, netdev@...r.kernel.org,
        linux-kernel@...r.kernel.org
Cc:     peterx@...hat.com, aarcange@...hat.com,
        James.Bottomley@...senpartnership.com, hch@...radead.org,
        davem@...emloft.net, jglisse@...hat.com, linux-mm@...ck.org,
        linux-arm-kernel@...ts.infradead.org, linux-parisc@...r.kernel.org,
        christophe.de.dinechin@...il.com, jrdr.linux@...il.com
Subject: [RFC PATCH V3 1/6] vhost: generalize adding used elem

Use one generic vhost_copy_to_user() instead of two dedicated
accessor. This will simplify the conversion to fine grain
accessors. About 2% improvement of PPS were seen during vitio-user
txonly test.

Signed-off-by: Jason Wang <jasowang@...hat.com>
---
 drivers/vhost/vhost.c | 11 +----------
 1 file changed, 1 insertion(+), 10 deletions(-)

diff --git a/drivers/vhost/vhost.c b/drivers/vhost/vhost.c
index 351af88231ad..6df76ac8200a 100644
--- a/drivers/vhost/vhost.c
+++ b/drivers/vhost/vhost.c
@@ -2255,16 +2255,7 @@ static int __vhost_add_used_n(struct vhost_virtqueue *vq,
 
 	start = vq->last_used_idx & (vq->num - 1);
 	used = vq->used->ring + start;
-	if (count == 1) {
-		if (vhost_put_user(vq, heads[0].id, &used->id)) {
-			vq_err(vq, "Failed to write used id");
-			return -EFAULT;
-		}
-		if (vhost_put_user(vq, heads[0].len, &used->len)) {
-			vq_err(vq, "Failed to write used len");
-			return -EFAULT;
-		}
-	} else if (vhost_copy_to_user(vq, used, heads, count * sizeof *used)) {
+	if (vhost_copy_to_user(vq, used, heads, count * sizeof *used)) {
 		vq_err(vq, "Failed to write used");
 		return -EFAULT;
 	}
-- 
2.18.1