diff mbox series

[v4] vhost: batch used descs chains write-back with packed ring

Message ID 20181220164755.8509-1-maxime.coquelin@redhat.com (mailing list archive)
State Accepted, archived
Delegated to: Maxime Coquelin
Headers
Series [v4] vhost: batch used descs chains write-back with packed ring |

Checks

Context Check Description
ci/Intel-compilation success Compilation OK
ci/mellanox-Performance-Testing success Performance Testing PASS
ci/intel-Performance-Testing success Performance Testing PASS

Commit Message

Maxime Coquelin Dec. 20, 2018, 4:47 p.m. UTC 
  Instead of writing back descriptors chains in order, let's
write the first chain flags last in order to improve batching.

Also, move the write barrier in logging cache sync, so that it
is done only when logging is enabled. It means there is now
one more barrier for split ring when logging is enabled.

With Kernel's pktgen benchmark, ~3% performance gain is measured.

Signed-off-by: Maxime Coquelin <maxime.coquelin@redhat.com>
---
 lib/librte_vhost/vhost.h      |  2 ++
 lib/librte_vhost/virtio_net.c | 19 ++++++++++++++++---
 2 files changed, 18 insertions(+), 3 deletions(-)

Comments

Michael S. Tsirkin Dec. 20, 2018, 6:19 p.m. UTC | #1 
On Thu, Dec 20, 2018 at 05:47:55PM +0100, Maxime Coquelin wrote:
> Instead of writing back descriptors chains in order, let's
> write the first chain flags last in order to improve batching.
> 
> Also, move the write barrier in logging cache sync, so that it
> is done only when logging is enabled. It means there is now
> one more barrier for split ring when logging is enabled.
> 
> With Kernel's pktgen benchmark, ~3% performance gain is measured.
> 
> Signed-off-by: Maxime Coquelin <maxime.coquelin@redhat.com>

Acked-by: Michael S. Tsirkin <mst@redhat.com>


> ---
>  lib/librte_vhost/vhost.h      |  2 ++
>  lib/librte_vhost/virtio_net.c | 19 ++++++++++++++++---
>  2 files changed, 18 insertions(+), 3 deletions(-)
> 
> diff --git a/lib/librte_vhost/vhost.h b/lib/librte_vhost/vhost.h
> index 3b3265c4b..7d1d8a308 100644
> --- a/lib/librte_vhost/vhost.h
> +++ b/lib/librte_vhost/vhost.h
> @@ -457,6 +457,8 @@ vhost_log_cache_sync(struct virtio_net *dev, struct vhost_virtqueue *vq)
>  		   !dev->log_base))
>  		return;
>  
> +	rte_smp_wmb();
> +
>  	log_base = (unsigned long *)(uintptr_t)dev->log_base;
>  
>  	/*
> diff --git a/lib/librte_vhost/virtio_net.c b/lib/librte_vhost/virtio_net.c
> index 8c657a101..02c1fd3a4 100644
> --- a/lib/librte_vhost/virtio_net.c
> +++ b/lib/librte_vhost/virtio_net.c
> @@ -97,6 +97,8 @@ flush_shadow_used_ring_packed(struct virtio_net *dev,
>  {
>  	int i;
>  	uint16_t used_idx = vq->last_used_idx;
> +	uint16_t head_idx = vq->last_used_idx;
> +	uint16_t head_flags = 0;
>  
>  	/* Split loop in two to save memory barriers */
>  	for (i = 0; i < vq->shadow_used_idx; i++) {
> @@ -126,12 +128,17 @@ flush_shadow_used_ring_packed(struct virtio_net *dev,
>  			flags &= ~VRING_DESC_F_AVAIL;
>  		}
>  
> -		vq->desc_packed[vq->last_used_idx].flags = flags;
> +		if (i > 0) {
> +			vq->desc_packed[vq->last_used_idx].flags = flags;
>  
> -		vhost_log_cache_used_vring(dev, vq,
> +			vhost_log_cache_used_vring(dev, vq,
>  					vq->last_used_idx *
>  					sizeof(struct vring_packed_desc),
>  					sizeof(struct vring_packed_desc));
> +		} else {
> +			head_idx = vq->last_used_idx;
> +			head_flags = flags;
> +		}
>  
>  		vq->last_used_idx += vq->shadow_used_packed[i].count;
>  		if (vq->last_used_idx >= vq->size) {
> @@ -140,7 +147,13 @@ flush_shadow_used_ring_packed(struct virtio_net *dev,
>  		}
>  	}
>  
> -	rte_smp_wmb();
> +	vq->desc_packed[head_idx].flags = head_flags;
> +
> +	vhost_log_cache_used_vring(dev, vq,
> +				head_idx *
> +				sizeof(struct vring_packed_desc),
> +				sizeof(struct vring_packed_desc));
> +
>  	vq->shadow_used_idx = 0;
>  	vhost_log_cache_sync(dev, vq);
>  }
> -- 
> 2.17.2
Tiwei Bie Dec. 21, 2018, 2:28 a.m. UTC | #2 
On Thu, Dec 20, 2018 at 05:47:55PM +0100, Maxime Coquelin wrote:
> Instead of writing back descriptors chains in order, let's
> write the first chain flags last in order to improve batching.
> 
> Also, move the write barrier in logging cache sync, so that it
> is done only when logging is enabled. It means there is now
> one more barrier for split ring when logging is enabled.
> 
> With Kernel's pktgen benchmark, ~3% performance gain is measured.
> 
> Signed-off-by: Maxime Coquelin <maxime.coquelin@redhat.com>
> ---
>  lib/librte_vhost/vhost.h      |  2 ++
>  lib/librte_vhost/virtio_net.c | 19 ++++++++++++++++---
>  2 files changed, 18 insertions(+), 3 deletions(-)
> 
> diff --git a/lib/librte_vhost/vhost.h b/lib/librte_vhost/vhost.h
> index 3b3265c4b..7d1d8a308 100644
> --- a/lib/librte_vhost/vhost.h
> +++ b/lib/librte_vhost/vhost.h
> @@ -457,6 +457,8 @@ vhost_log_cache_sync(struct virtio_net *dev, struct vhost_virtqueue *vq)
>  		   !dev->log_base))
>  		return;
>  
> +	rte_smp_wmb();

Better to also remove below comments (which can be done
when applying the patch):

https://github.com/DPDK/dpdk/blob/dafc04c15174/lib/librte_vhost/vhost.h#L461-L464

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

> +
>  	log_base = (unsigned long *)(uintptr_t)dev->log_base;
>  
>  	/*
> diff --git a/lib/librte_vhost/virtio_net.c b/lib/librte_vhost/virtio_net.c
> index 8c657a101..02c1fd3a4 100644
> --- a/lib/librte_vhost/virtio_net.c
> +++ b/lib/librte_vhost/virtio_net.c
> @@ -97,6 +97,8 @@ flush_shadow_used_ring_packed(struct virtio_net *dev,
>  {
>  	int i;
>  	uint16_t used_idx = vq->last_used_idx;
> +	uint16_t head_idx = vq->last_used_idx;
> +	uint16_t head_flags = 0;
>  
>  	/* Split loop in two to save memory barriers */
>  	for (i = 0; i < vq->shadow_used_idx; i++) {
> @@ -126,12 +128,17 @@ flush_shadow_used_ring_packed(struct virtio_net *dev,
>  			flags &= ~VRING_DESC_F_AVAIL;
>  		}
>  
> -		vq->desc_packed[vq->last_used_idx].flags = flags;
> +		if (i > 0) {
> +			vq->desc_packed[vq->last_used_idx].flags = flags;
>  
> -		vhost_log_cache_used_vring(dev, vq,
> +			vhost_log_cache_used_vring(dev, vq,
>  					vq->last_used_idx *
>  					sizeof(struct vring_packed_desc),
>  					sizeof(struct vring_packed_desc));
> +		} else {
> +			head_idx = vq->last_used_idx;
> +			head_flags = flags;
> +		}
>  
>  		vq->last_used_idx += vq->shadow_used_packed[i].count;
>  		if (vq->last_used_idx >= vq->size) {
> @@ -140,7 +147,13 @@ flush_shadow_used_ring_packed(struct virtio_net *dev,
>  		}
>  	}
>  
> -	rte_smp_wmb();
> +	vq->desc_packed[head_idx].flags = head_flags;
> +
> +	vhost_log_cache_used_vring(dev, vq,
> +				head_idx *
> +				sizeof(struct vring_packed_desc),
> +				sizeof(struct vring_packed_desc));
> +
>  	vq->shadow_used_idx = 0;
>  	vhost_log_cache_sync(dev, vq);
>  }
> -- 
> 2.17.2
>
Maxime Coquelin Dec. 21, 2018, 9:20 a.m. UTC | #3 
On 12/20/18 5:47 PM, Maxime Coquelin wrote:
> Instead of writing back descriptors chains in order, let's
> write the first chain flags last in order to improve batching.
> 
> Also, move the write barrier in logging cache sync, so that it
> is done only when logging is enabled. It means there is now
> one more barrier for split ring when logging is enabled.
> 
> With Kernel's pktgen benchmark, ~3% performance gain is measured.
> 
> Signed-off-by: Maxime Coquelin<maxime.coquelin@redhat.com>
> ---
>   lib/librte_vhost/vhost.h      |  2 ++
>   lib/librte_vhost/virtio_net.c | 19 ++++++++++++++++---
>   2 files changed, 18 insertions(+), 3 deletions(-)

Applied to dpdk-next-virtio

Maxime
diff mbox series

Patch

diff --git a/lib/librte_vhost/vhost.h b/lib/librte_vhost/vhost.h
index 3b3265c4b..7d1d8a308 100644
--- a/lib/librte_vhost/vhost.h
+++ b/lib/librte_vhost/vhost.h
@@ -457,6 +457,8 @@  vhost_log_cache_sync(struct virtio_net *dev, struct vhost_virtqueue *vq)
 		   !dev->log_base))
 		return;
 
+	rte_smp_wmb();
+
 	log_base = (unsigned long *)(uintptr_t)dev->log_base;
 
 	/*
diff --git a/lib/librte_vhost/virtio_net.c b/lib/librte_vhost/virtio_net.c
index 8c657a101..02c1fd3a4 100644
--- a/lib/librte_vhost/virtio_net.c
+++ b/lib/librte_vhost/virtio_net.c
@@ -97,6 +97,8 @@  flush_shadow_used_ring_packed(struct virtio_net *dev,
 {
 	int i;
 	uint16_t used_idx = vq->last_used_idx;
+	uint16_t head_idx = vq->last_used_idx;
+	uint16_t head_flags = 0;
 
 	/* Split loop in two to save memory barriers */
 	for (i = 0; i < vq->shadow_used_idx; i++) {
@@ -126,12 +128,17 @@  flush_shadow_used_ring_packed(struct virtio_net *dev,
 			flags &= ~VRING_DESC_F_AVAIL;
 		}
 
-		vq->desc_packed[vq->last_used_idx].flags = flags;
+		if (i > 0) {
+			vq->desc_packed[vq->last_used_idx].flags = flags;
 
-		vhost_log_cache_used_vring(dev, vq,
+			vhost_log_cache_used_vring(dev, vq,
 					vq->last_used_idx *
 					sizeof(struct vring_packed_desc),
 					sizeof(struct vring_packed_desc));
+		} else {
+			head_idx = vq->last_used_idx;
+			head_flags = flags;
+		}
 
 		vq->last_used_idx += vq->shadow_used_packed[i].count;
 		if (vq->last_used_idx >= vq->size) {
@@ -140,7 +147,13 @@  flush_shadow_used_ring_packed(struct virtio_net *dev,
 		}
 	}
 
-	rte_smp_wmb();
+	vq->desc_packed[head_idx].flags = head_flags;
+
+	vhost_log_cache_used_vring(dev, vq,
+				head_idx *
+				sizeof(struct vring_packed_desc),
+				sizeof(struct vring_packed_desc));
+
 	vq->shadow_used_idx = 0;
 	vhost_log_cache_sync(dev, vq);
 }