[PATCH v2 1/1] VSOCK: remove more space available check filling TX vq

[PATCH v2 1/1] VSOCK: remove more space available check filling TX vq

[ggarcia]

From: Gerard Garcia <ggarcia@deic.uab.cat>

Remove unnecessary use of enable/disable callback notifications
and the incorrect more space available check.

The virtio_transport_tx_work handles when the TX virtqueue
has more buffers available.

Signed-off-by: Gerard Garcia <ggarcia@deic.uab.cat>
Acked-by: Stefan Hajnoczi <stefanha@redhat.com>
---

v2:
 * Comment style.

 net/vmw_vsock/virtio_transport.c | 10 +++-------
 1 file changed, 3 insertions(+), 7 deletions(-)

diff --git a/net/vmw_vsock/virtio_transport.c b/net/vmw_vsock/virtio_transport.c
index 699dfab..936d7ee 100644
--- a/net/vmw_vsock/virtio_transport.c
+++ b/net/vmw_vsock/virtio_transport.c
@@ -87,9 +87,6 @@ virtio_transport_send_pkt_work(struct work_struct *work)
 
 	vq = vsock->vqs[VSOCK_VQ_TX];
 
-	/* Avoid unnecessary interrupts while we're processing the ring */
-	virtqueue_disable_cb(vq);
-
 	for (;;) {
 		struct virtio_vsock_pkt *pkt;
 		struct scatterlist hdr, buf, *sgs[2];
@@ -99,7 +96,6 @@ virtio_transport_send_pkt_work(struct work_struct *work)
 		spin_lock_bh(&vsock->send_pkt_list_lock);
 		if (list_empty(&vsock->send_pkt_list)) {
 			spin_unlock_bh(&vsock->send_pkt_list_lock);
-			virtqueue_enable_cb(vq);
 			break;
 		}
 
@@ -118,13 +114,13 @@ virtio_transport_send_pkt_work(struct work_struct *work)
 		}
 
 		ret = virtqueue_add_sgs(vq, sgs, out_sg, in_sg, pkt, GFP_KERNEL);
+		/* Usually this means that there is no more space available in
+		 * the vq
+		 */
 		if (ret < 0) {
 			spin_lock_bh(&vsock->send_pkt_list_lock);
 			list_add(&pkt->list, &vsock->send_pkt_list);
 			spin_unlock_bh(&vsock->send_pkt_list_lock);
-
-			if (!virtqueue_enable_cb(vq) && ret == -ENOSPC)
-				continue; /* retry now that we have more space */
 			break;
 		}
 
-- 
2.9.1

Re: [PATCH v2 1/1] VSOCK: remove more space available check filling TX vq

[David Miller]

From: ggarcia@abra.uab.cat
Date: Wed, 10 Aug 2016 17:24:34 +0200

> From: Gerard Garcia <ggarcia@deic.uab.cat>
> 
> Remove unnecessary use of enable/disable callback notifications
> and the incorrect more space available check.
> 
> The virtio_transport_tx_work handles when the TX virtqueue
> has more buffers available.
> 
> Signed-off-by: Gerard Garcia <ggarcia@deic.uab.cat>
> Acked-by: Stefan Hajnoczi <stefanha@redhat.com>

This does not apply cleanly to the current net GIT tree.

Re: [PATCH v2 1/1] VSOCK: remove more space available check filling TXvq

[Gerard Garcia]

On 08/13/2016 02:31 AM, David Miller wrote:
> From: ggarcia@abra.uab.cat
> Date: Wed, 10 Aug 2016 17:24:34 +0200
>
>> From: Gerard Garcia <ggarcia@deic.uab.cat>
>>
>> Remove unnecessary use of enable/disable callback notifications
>> and the incorrect more space available check.
>>
>> The virtio_transport_tx_work handles when the TX virtqueue
>> has more buffers available.
>>
>> Signed-off-by: Gerard Garcia <ggarcia@deic.uab.cat>
>> Acked-by: Stefan Hajnoczi <stefanha@redhat.com>
>
> This does not apply cleanly to the current net GIT tree.
>

I'm sorry, I should have said that it applies over the mst vhost tree.

Re: [PATCH v2 1/1] VSOCK: remove more space available check filling TX vq

[Michael S. Tsirkin]

On Wed, Aug 10, 2016 at 05:24:34PM +0200, ggarcia@abra.uab.cat wrote:
> From: Gerard Garcia <ggarcia@deic.uab.cat>
> 
> Remove unnecessary use of enable/disable callback notifications
> and the incorrect more space available check.
> 
> The virtio_transport_tx_work handles when the TX virtqueue
> has more buffers available.
> 
> Signed-off-by: Gerard Garcia <ggarcia@deic.uab.cat>
> Acked-by: Stefan Hajnoczi <stefanha@redhat.com>

Generally enable/disable is a worthwhile optimization,
but if Stefan wants to keep code simple for now,
I don't have a problem with that.

> ---
> 
> v2:
>  * Comment style.
> 
>  net/vmw_vsock/virtio_transport.c | 10 +++-------
>  1 file changed, 3 insertions(+), 7 deletions(-)
> 
> diff --git a/net/vmw_vsock/virtio_transport.c b/net/vmw_vsock/virtio_transport.c
> index 699dfab..936d7ee 100644
> --- a/net/vmw_vsock/virtio_transport.c
> +++ b/net/vmw_vsock/virtio_transport.c
> @@ -87,9 +87,6 @@ virtio_transport_send_pkt_work(struct work_struct *work)
>  
>  	vq = vsock->vqs[VSOCK_VQ_TX];
>  
> -	/* Avoid unnecessary interrupts while we're processing the ring */
> -	virtqueue_disable_cb(vq);
> -
>  	for (;;) {
>  		struct virtio_vsock_pkt *pkt;
>  		struct scatterlist hdr, buf, *sgs[2];
> @@ -99,7 +96,6 @@ virtio_transport_send_pkt_work(struct work_struct *work)
>  		spin_lock_bh(&vsock->send_pkt_list_lock);
>  		if (list_empty(&vsock->send_pkt_list)) {
>  			spin_unlock_bh(&vsock->send_pkt_list_lock);
> -			virtqueue_enable_cb(vq);
>  			break;
>  		}
>  
> @@ -118,13 +114,13 @@ virtio_transport_send_pkt_work(struct work_struct *work)
>  		}
>  
>  		ret = virtqueue_add_sgs(vq, sgs, out_sg, in_sg, pkt, GFP_KERNEL);
> +		/* Usually this means that there is no more space available in
> +		 * the vq
> +		 */
>  		if (ret < 0) {
>  			spin_lock_bh(&vsock->send_pkt_list_lock);
>  			list_add(&pkt->list, &vsock->send_pkt_list);
>  			spin_unlock_bh(&vsock->send_pkt_list_lock);
> -
> -			if (!virtqueue_enable_cb(vq) && ret == -ENOSPC)
> -				continue; /* retry now that we have more space */
>  			break;
>  		}
>  
> -- 
> 2.9.1

Re: [PATCH v2 1/1] VSOCK: remove more space available check filling TX vq

[Stefan Hajnoczi]

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On Mon, Aug 15, 2016 at 02:16:51AM +0300, Michael S. Tsirkin wrote:
> On Wed, Aug 10, 2016 at 05:24:34PM +0200, ggarcia@abra.uab.cat wrote:
> > From: Gerard Garcia <ggarcia@deic.uab.cat>
> > 
> > Remove unnecessary use of enable/disable callback notifications
> > and the incorrect more space available check.
> > 
> > The virtio_transport_tx_work handles when the TX virtqueue
> > has more buffers available.
> > 
> > Signed-off-by: Gerard Garcia <ggarcia@deic.uab.cat>
> > Acked-by: Stefan Hajnoczi <stefanha@redhat.com>
> 
> Generally enable/disable is a worthwhile optimization,
> but if Stefan wants to keep code simple for now,
> I don't have a problem with that.

Enabling/disabling callbacks is inappropriate in this function because
its job is *submitting* buffers rather than *reclaiming* completed
buffers.  Oops, I'm not sure how this mistake crept in :).

The callback suppression should only be done around the loop that
reclaims buffers.  Doing it in the wrong place leads to hangs if
interrupts are lost.

Stefan

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