Re: [V2 PATCH 9/9] vhost: zerocopy: poll vq in zerocopy callback

From: Jason Wang
Date: Tue May 15 2012 - 22:58:57 EST

On 05/16/2012 12:50 AM, Shirley Ma wrote:
On Wed, 2012-05-02 at 11:42 +0800, Jason Wang wrote:
We add used and signal guest in worker thread but did not poll the
during the zero copy callback. This may lead the missing of adding and
signalling during zerocopy. Solve this by polling the virtqueue and
let it
wakeup the worker during callback.

Signed-off-by: Jason Wang<jasowang@xxxxxxxxxx>
drivers/vhost/vhost.c | 1 +
1 files changed, 1 insertions(+), 0 deletions(-)

diff --git a/drivers/vhost/vhost.c b/drivers/vhost/vhost.c
index 947f00d..7b75fdf 100644
--- a/drivers/vhost/vhost.c
+++ b/drivers/vhost/vhost.c
@@ -1604,6 +1604,7 @@ void vhost_zerocopy_callback(void *arg)
struct vhost_ubuf_ref *ubufs = ubuf->arg;
struct vhost_virtqueue *vq = ubufs->vq;

+ vhost_poll_queue(&vq->poll);
/* set len = 1 to mark this desc buffers done DMA */
vq->heads[ubuf->desc].len = VHOST_DMA_DONE_LEN;
kref_put(&ubufs->kref, vhost_zerocopy_done_signal);
Doing so, we might have redundant vhost_poll_queue(). Do you know in
which scenario there might be missing of adding and signaling during

Yes, as we only do signaling and adding during tx work, if there's no tx work when the skb were sent, we may lose the opportunity to let guest know about the completion. It's easy to be reproduced with netperf test.


To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@xxxxxxxxxxxxxxx
More majordomo info at
Please read the FAQ at