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* [dpdk-dev] [PATCH v2] vhost: avoid memory barriers when no descriptors dequeued
@ 2018-10-23 10:07 Maxime Coquelin
  2018-10-23 12:39 ` [dpdk-dev] [dpdk-stable] " Jens Freimann
                   ` (2 more replies)
  0 siblings, 3 replies; 4+ messages in thread
From: Maxime Coquelin @ 2018-10-23 10:07 UTC (permalink / raw)
  To: dev, tiwei.bie, jfreimann, zhihong.wang; +Cc: Maxime Coquelin, stable

In both split and packed dequeue paths, flush_shadow_used_ring
and vhost_ring_call variants gets called even if not packets
have been dequeued, and so no descriptors updates happened.

It has an impact on CPU pipeline, as memory barriers are used
in these functions.

This patch don't call these functions if no descriptors have
been dequeued. The performance gain with split ring when
dequeue zero-copy is disabled should be null, but should be
noticeable with packed ring or dequeue zero-copy enabled.

Fixes: ae999ce49dcb ("vhost: add Tx support for packed ring")
Fixes: 915cf9404225 ("vhost: use shadow used ring in dequeue path")
Cc: stable@dpdk.org

Signed-off-by: Maxime Coquelin <maxime.coquelin@redhat.com>
---

Changes in v2:
- Fix shadow_used_idx reset in error path (Tiwei)

 lib/librte_vhost/virtio_net.c | 24 ++++++++++++++++--------
 1 file changed, 16 insertions(+), 8 deletions(-)

diff --git a/lib/librte_vhost/virtio_net.c b/lib/librte_vhost/virtio_net.c
index 1c31c0562..8ad30c94a 100644
--- a/lib/librte_vhost/virtio_net.c
+++ b/lib/librte_vhost/virtio_net.c
@@ -1360,8 +1360,10 @@ virtio_dev_tx_split(struct virtio_net *dev, struct vhost_virtqueue *vq,
 			}
 		}
 
-		flush_shadow_used_ring_split(dev, vq);
-		vhost_vring_call_split(dev, vq);
+		if (likely(vq->shadow_used_idx)) {
+			flush_shadow_used_ring_split(dev, vq);
+			vhost_vring_call_split(dev, vq);
+		}
 	}
 
 	rte_prefetch0(&vq->avail->ring[vq->last_avail_idx & (vq->size - 1)]);
@@ -1440,8 +1442,10 @@ virtio_dev_tx_split(struct virtio_net *dev, struct vhost_virtqueue *vq,
 		do_data_copy_dequeue(vq);
 		if (unlikely(i < count))
 			vq->shadow_used_idx = i;
-		flush_shadow_used_ring_split(dev, vq);
-		vhost_vring_call_split(dev, vq);
+		if (likely(vq->shadow_used_idx)) {
+			flush_shadow_used_ring_split(dev, vq);
+			vhost_vring_call_split(dev, vq);
+		}
 	}
 
 	return i;
@@ -1476,8 +1480,10 @@ virtio_dev_tx_packed(struct virtio_net *dev, struct vhost_virtqueue *vq,
 			}
 		}
 
-		flush_shadow_used_ring_packed(dev, vq);
-		vhost_vring_call_packed(dev, vq);
+		if (likely(vq->shadow_used_idx)) {
+			flush_shadow_used_ring_packed(dev, vq);
+			vhost_vring_call_packed(dev, vq);
+		}
 	}
 
 	VHOST_LOG_DEBUG(VHOST_DATA, "(%d) %s\n", dev->vid, __func__);
@@ -1555,8 +1561,10 @@ virtio_dev_tx_packed(struct virtio_net *dev, struct vhost_virtqueue *vq,
 		do_data_copy_dequeue(vq);
 		if (unlikely(i < count))
 			vq->shadow_used_idx = i;
-		flush_shadow_used_ring_packed(dev, vq);
-		vhost_vring_call_packed(dev, vq);
+		if (likely(vq->shadow_used_idx)) {
+			flush_shadow_used_ring_packed(dev, vq);
+			vhost_vring_call_packed(dev, vq);
+		}
 	}
 
 	return i;
-- 
2.17.1

^ permalink raw reply	[flat|nested] 4+ messages in thread

* Re: [dpdk-dev] [dpdk-stable] [PATCH v2] vhost: avoid memory barriers when no descriptors dequeued
  2018-10-23 10:07 [dpdk-dev] [PATCH v2] vhost: avoid memory barriers when no descriptors dequeued Maxime Coquelin
@ 2018-10-23 12:39 ` Jens Freimann
  2018-10-24  8:50 ` [dpdk-dev] " Tiwei Bie
  2018-10-24 10:51 ` Maxime Coquelin
  2 siblings, 0 replies; 4+ messages in thread
From: Jens Freimann @ 2018-10-23 12:39 UTC (permalink / raw)
  To: Maxime Coquelin; +Cc: dev, tiwei.bie, zhihong.wang, stable

On Tue, Oct 23, 2018 at 12:07:10PM +0200, Maxime Coquelin wrote:
>In both split and packed dequeue paths, flush_shadow_used_ring
>and vhost_ring_call variants gets called even if not packets
>have been dequeued, and so no descriptors updates happened.
>
>It has an impact on CPU pipeline, as memory barriers are used
>in these functions.
>
>This patch don't call these functions if no descriptors have
>been dequeued. The performance gain with split ring when
>dequeue zero-copy is disabled should be null, but should be
>noticeable with packed ring or dequeue zero-copy enabled.

I tried this with packed ring pmd patch series v8 and it works fine.
It doesn't hurt performance either, I see improvements in sending
packets from guest to host. 

Reviewed-by: Jens Freimann <jfreimann@redhat.com> 
Tested-by: Jens Freimann <jfreimann@redhat.com>

regards,
Jens 

^ permalink raw reply	[flat|nested] 4+ messages in thread

* Re: [dpdk-dev] [PATCH v2] vhost: avoid memory barriers when no descriptors dequeued
  2018-10-23 10:07 [dpdk-dev] [PATCH v2] vhost: avoid memory barriers when no descriptors dequeued Maxime Coquelin
  2018-10-23 12:39 ` [dpdk-dev] [dpdk-stable] " Jens Freimann
@ 2018-10-24  8:50 ` Tiwei Bie
  2018-10-24 10:51 ` Maxime Coquelin
  2 siblings, 0 replies; 4+ messages in thread
From: Tiwei Bie @ 2018-10-24  8:50 UTC (permalink / raw)
  To: Maxime Coquelin; +Cc: dev, jfreimann, zhihong.wang, stable

On Tue, Oct 23, 2018 at 12:07:10PM +0200, Maxime Coquelin wrote:
> In both split and packed dequeue paths, flush_shadow_used_ring
> and vhost_ring_call variants gets called even if not packets
> have been dequeued, and so no descriptors updates happened.
> 
> It has an impact on CPU pipeline, as memory barriers are used
> in these functions.
> 
> This patch don't call these functions if no descriptors have
> been dequeued. The performance gain with split ring when
> dequeue zero-copy is disabled should be null, but should be
> noticeable with packed ring or dequeue zero-copy enabled.
> 
> Fixes: ae999ce49dcb ("vhost: add Tx support for packed ring")
> Fixes: 915cf9404225 ("vhost: use shadow used ring in dequeue path")
> Cc: stable@dpdk.org
> 
> Signed-off-by: Maxime Coquelin <maxime.coquelin@redhat.com>
> ---
> 
> Changes in v2:
> - Fix shadow_used_idx reset in error path (Tiwei)
> 
>  lib/librte_vhost/virtio_net.c | 24 ++++++++++++++++--------
>  1 file changed, 16 insertions(+), 8 deletions(-)

Reviewed-by: Tiwei Bie <tiwei.bie@intel.com>

^ permalink raw reply	[flat|nested] 4+ messages in thread

* Re: [dpdk-dev] [PATCH v2] vhost: avoid memory barriers when no descriptors dequeued
  2018-10-23 10:07 [dpdk-dev] [PATCH v2] vhost: avoid memory barriers when no descriptors dequeued Maxime Coquelin
  2018-10-23 12:39 ` [dpdk-dev] [dpdk-stable] " Jens Freimann
  2018-10-24  8:50 ` [dpdk-dev] " Tiwei Bie
@ 2018-10-24 10:51 ` Maxime Coquelin
  2 siblings, 0 replies; 4+ messages in thread
From: Maxime Coquelin @ 2018-10-24 10:51 UTC (permalink / raw)
  To: dev, tiwei.bie, jfreimann, zhihong.wang; +Cc: stable



On 10/23/18 12:07 PM, Maxime Coquelin wrote:
> In both split and packed dequeue paths, flush_shadow_used_ring
> and vhost_ring_call variants gets called even if not packets
> have been dequeued, and so no descriptors updates happened.
> 
> It has an impact on CPU pipeline, as memory barriers are used
> in these functions.
> 
> This patch don't call these functions if no descriptors have
> been dequeued. The performance gain with split ring when
> dequeue zero-copy is disabled should be null, but should be
> noticeable with packed ring or dequeue zero-copy enabled.
> 
> Fixes: ae999ce49dcb ("vhost: add Tx support for packed ring")
> Fixes: 915cf9404225 ("vhost: use shadow used ring in dequeue path")
> Cc:stable@dpdk.org
> 
> Signed-off-by: Maxime Coquelin<maxime.coquelin@redhat.com>
> ---
> 
> Changes in v2:
> - Fix shadow_used_idx reset in error path (Tiwei)
> 
>   lib/librte_vhost/virtio_net.c | 24 ++++++++++++++++--------
>   1 file changed, 16 insertions(+), 8 deletions(-)


Applied to dpdk-next-virtio/master.

Maxime

^ permalink raw reply	[flat|nested] 4+ messages in thread

end of thread, other threads:[~2018-10-24 10:51 UTC | newest]

Thread overview: 4+ messages (download: mbox.gz / follow: Atom feed)
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2018-10-23 10:07 [dpdk-dev] [PATCH v2] vhost: avoid memory barriers when no descriptors dequeued Maxime Coquelin
2018-10-23 12:39 ` [dpdk-dev] [dpdk-stable] " Jens Freimann
2018-10-24  8:50 ` [dpdk-dev] " Tiwei Bie
2018-10-24 10:51 ` Maxime Coquelin

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