netdev - [PATCHv2 net-next 5/8] vhost: track zero copy failures using DMA length

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Date:	Wed, 31 Oct 2012 12:31:31 +0200
From:	"Michael S. Tsirkin" <mst@...hat.com>
To:	unlisted-recipients:; (no To-header on input)
Cc:	Vlad Yasevich <vyasevic@...hat.com>,
	"David S. Miller" <davem@...emloft.net>,
	Eric Dumazet <edumazet@...gle.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Alexander Duyck <alexander.h.duyck@...el.com>,
	Ian Campbell <Ian.Campbell@...rix.com>, kvm@...r.kernel.org,
	virtualization@...ts.linux-foundation.org, netdev@...r.kernel.org,
	linux-kernel@...r.kernel.org
Subject: [PATCHv2 net-next 5/8] vhost: track zero copy failures using DMA
 length

This will be used to disable zerocopy when error rate
is high.

Signed-off-by: Michael S. Tsirkin <mst@...hat.com>
---
 drivers/vhost/vhost.c | 7 ++++---
 drivers/vhost/vhost.h | 4 ++++
 2 files changed, 8 insertions(+), 3 deletions(-)

diff --git a/drivers/vhost/vhost.c b/drivers/vhost/vhost.c
index 906fd9f..5affce3 100644
--- a/drivers/vhost/vhost.c
+++ b/drivers/vhost/vhost.c
@@ -425,7 +425,7 @@ int vhost_zerocopy_signal_used(struct vhost_virtqueue *vq)
 	int j = 0;
 
 	for (i = vq->done_idx; i != vq->upend_idx; i = (i + 1) % UIO_MAXIOV) {
-		if ((vq->heads[i].len == VHOST_DMA_DONE_LEN)) {
+		if (VHOST_DMA_IS_DONE(vq->heads[i].len)) {
 			vq->heads[i].len = VHOST_DMA_CLEAR_LEN;
 			vhost_add_used_and_signal(vq->dev, vq,
 						  vq->heads[i].id, 0);
@@ -1600,13 +1600,14 @@ void vhost_ubuf_put_and_wait(struct vhost_ubuf_ref *ubufs)
 	kfree(ubufs);
 }
 
-void vhost_zerocopy_callback(struct ubuf_info *ubuf, int zerocopy_status)
+void vhost_zerocopy_callback(struct ubuf_info *ubuf, int status)
 {
 	struct vhost_ubuf_ref *ubufs = ubuf->ctx;
 	struct vhost_virtqueue *vq = ubufs->vq;
 
 	vhost_poll_queue(&vq->poll);
 	/* set len to mark this desc buffers done DMA */
-	vq->heads[ubuf->desc].len = VHOST_DMA_DONE_LEN;
+	vq->heads[ubuf->desc].len = status ?
+		VHOST_DMA_FAILED_LEN : VHOST_DMA_DONE_LEN;
 	kref_put(&ubufs->kref, vhost_zerocopy_done_signal);
 }
diff --git a/drivers/vhost/vhost.h b/drivers/vhost/vhost.h
index ad72a1f..6fdf31d 100644
--- a/drivers/vhost/vhost.h
+++ b/drivers/vhost/vhost.h
@@ -17,6 +17,8 @@
  * For transmit, used buffer len is unused; we override it to track buffer
  * status internally; used for zerocopy tx only.
  */
+/* Lower device DMA failed */
+#define VHOST_DMA_FAILED_LEN	3
 /* Lower device DMA done */
 #define VHOST_DMA_DONE_LEN	2
 /* Lower device DMA in progress */
@@ -24,6 +26,8 @@
 /* Buffer unused */
 #define VHOST_DMA_CLEAR_LEN	0
 
+#define VHOST_DMA_IS_DONE(len) ((len) >= VHOST_DMA_DONE_LEN)
+
 struct vhost_device;
 
 struct vhost_work;
-- 
MST

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