[virtio-dev] [PATCH v3 0/2] Improve virtio performance for 9k mtu

[virtio-dev] [PATCH v3 0/2] Improve virtio performance for 9k mtu

[Gavin Li]

This small series contains two patches that improves virtio netdevice
performance for 9K mtu when GRO/ guest TSO is disabled.

Gavin Li (2):
  virtio-net: introduce and use helper function for guest gso support
    checks
  virtio-net: use mtu size as buffer length for big packets

 drivers/net/virtio_net.c | 48 ++++++++++++++++++++++++++--------------
 1 file changed, 32 insertions(+), 16 deletions(-)

-- 
2.31.1


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[virtio-dev] [PATCH v3 1/2] virtio-net: introduce and use helper function for guest gso support checks

[Gavin Li]

Probe routine is already several hundred lines.
Use helper function for guest gso support check.

Signed-off-by: Gavin Li <gavinl@nvidia.com>
Reviewed-by: Gavi Teitz <gavi@nvidia.com>
Reviewed-by: Parav Pandit <parav@nvidia.com>
---
changelog:
v1->v2
- Add new patch
---
 drivers/net/virtio_net.c | 13 +++++++++----
 1 file changed, 9 insertions(+), 4 deletions(-)

diff --git a/drivers/net/virtio_net.c b/drivers/net/virtio_net.c
index 9cce7dec7366..e1904877d461 100644
--- a/drivers/net/virtio_net.c
+++ b/drivers/net/virtio_net.c
@@ -3682,6 +3682,14 @@ static int virtnet_validate(struct virtio_device *vdev)
 	return 0;
 }
 
+static bool virtnet_check_guest_gso(const struct virtnet_info *vi)
+{
+	return (virtio_has_feature(vi->vdev, VIRTIO_NET_F_GUEST_TSO4) ||
+		virtio_has_feature(vi->vdev, VIRTIO_NET_F_GUEST_TSO6) ||
+		virtio_has_feature(vi->vdev, VIRTIO_NET_F_GUEST_ECN) ||
+		virtio_has_feature(vi->vdev, VIRTIO_NET_F_GUEST_UFO));
+}
+
 static int virtnet_probe(struct virtio_device *vdev)
 {
 	int i, err = -ENOMEM;
@@ -3777,10 +3785,7 @@ static int virtnet_probe(struct virtio_device *vdev)
 	spin_lock_init(&vi->refill_lock);
 
 	/* If we can receive ANY GSO packets, we must allocate large ones. */
-	if (virtio_has_feature(vdev, VIRTIO_NET_F_GUEST_TSO4) ||
-	    virtio_has_feature(vdev, VIRTIO_NET_F_GUEST_TSO6) ||
-	    virtio_has_feature(vdev, VIRTIO_NET_F_GUEST_ECN) ||
-	    virtio_has_feature(vdev, VIRTIO_NET_F_GUEST_UFO))
+	if (virtnet_check_guest_gso(vi))
 		vi->big_packets = true;
 
 	if (virtio_has_feature(vdev, VIRTIO_NET_F_MRG_RXBUF))
-- 
2.31.1


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[virtio-dev] Re: [PATCH v3 1/2] virtio-net: introduce and use helper function for guest gso support checks

[Xuan Zhuo]

On Tue, 30 Aug 2022 05:26:33 +0300, Gavin Li <gavinl@nvidia.com> wrote:
> Probe routine is already several hundred lines.
> Use helper function for guest gso support check.
>
> Signed-off-by: Gavin Li <gavinl@nvidia.com>
> Reviewed-by: Gavi Teitz <gavi@nvidia.com>
> Reviewed-by: Parav Pandit <parav@nvidia.com>


Reviewed-by: Xuan Zhuo <xuanzhuo@linux.alibaba.com>

> ---
> changelog:
> v1->v2
> - Add new patch
> ---
>  drivers/net/virtio_net.c | 13 +++++++++----
>  1 file changed, 9 insertions(+), 4 deletions(-)
>
> diff --git a/drivers/net/virtio_net.c b/drivers/net/virtio_net.c
> index 9cce7dec7366..e1904877d461 100644
> --- a/drivers/net/virtio_net.c
> +++ b/drivers/net/virtio_net.c
> @@ -3682,6 +3682,14 @@ static int virtnet_validate(struct virtio_device *vdev)
>  	return 0;
>  }
>
> +static bool virtnet_check_guest_gso(const struct virtnet_info *vi)
> +{
> +	return (virtio_has_feature(vi->vdev, VIRTIO_NET_F_GUEST_TSO4) ||
> +		virtio_has_feature(vi->vdev, VIRTIO_NET_F_GUEST_TSO6) ||
> +		virtio_has_feature(vi->vdev, VIRTIO_NET_F_GUEST_ECN) ||
> +		virtio_has_feature(vi->vdev, VIRTIO_NET_F_GUEST_UFO));
> +}
> +
>  static int virtnet_probe(struct virtio_device *vdev)
>  {
>  	int i, err = -ENOMEM;
> @@ -3777,10 +3785,7 @@ static int virtnet_probe(struct virtio_device *vdev)
>  	spin_lock_init(&vi->refill_lock);
>
>  	/* If we can receive ANY GSO packets, we must allocate large ones. */
> -	if (virtio_has_feature(vdev, VIRTIO_NET_F_GUEST_TSO4) ||
> -	    virtio_has_feature(vdev, VIRTIO_NET_F_GUEST_TSO6) ||
> -	    virtio_has_feature(vdev, VIRTIO_NET_F_GUEST_ECN) ||
> -	    virtio_has_feature(vdev, VIRTIO_NET_F_GUEST_UFO))
> +	if (virtnet_check_guest_gso(vi))
>  		vi->big_packets = true;
>
>  	if (virtio_has_feature(vdev, VIRTIO_NET_F_MRG_RXBUF))
> --
> 2.31.1
>

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Re: [virtio-dev] [PATCH v3 1/2] virtio-net: introduce and use helper function for guest gso support checks

[Si-Wei Liu]

On 8/29/2022 7:26 PM, Gavin Li wrote:
> Probe routine is already several hundred lines.
> Use helper function for guest gso support check.
>
> Signed-off-by: Gavin Li <gavinl@nvidia.com>
> Reviewed-by: Gavi Teitz <gavi@nvidia.com>
> Reviewed-by: Parav Pandit <parav@nvidia.com>
Reviewed-by: Si-Wei Liu <si-wei.liu@oracle.com>
> ---
> changelog:
> v1->v2
> - Add new patch
> ---
>   drivers/net/virtio_net.c | 13 +++++++++----
>   1 file changed, 9 insertions(+), 4 deletions(-)
>
> diff --git a/drivers/net/virtio_net.c b/drivers/net/virtio_net.c
> index 9cce7dec7366..e1904877d461 100644
> --- a/drivers/net/virtio_net.c
> +++ b/drivers/net/virtio_net.c
> @@ -3682,6 +3682,14 @@ static int virtnet_validate(struct virtio_device *vdev)
>   	return 0;
>   }
>   
> +static bool virtnet_check_guest_gso(const struct virtnet_info *vi)
> +{
> +	return (virtio_has_feature(vi->vdev, VIRTIO_NET_F_GUEST_TSO4) ||
> +		virtio_has_feature(vi->vdev, VIRTIO_NET_F_GUEST_TSO6) ||
> +		virtio_has_feature(vi->vdev, VIRTIO_NET_F_GUEST_ECN) ||
> +		virtio_has_feature(vi->vdev, VIRTIO_NET_F_GUEST_UFO));
> +}
> +
>   static int virtnet_probe(struct virtio_device *vdev)
>   {
>   	int i, err = -ENOMEM;
> @@ -3777,10 +3785,7 @@ static int virtnet_probe(struct virtio_device *vdev)
>   	spin_lock_init(&vi->refill_lock);
>   
>   	/* If we can receive ANY GSO packets, we must allocate large ones. */
> -	if (virtio_has_feature(vdev, VIRTIO_NET_F_GUEST_TSO4) ||
> -	    virtio_has_feature(vdev, VIRTIO_NET_F_GUEST_TSO6) ||
> -	    virtio_has_feature(vdev, VIRTIO_NET_F_GUEST_ECN) ||
> -	    virtio_has_feature(vdev, VIRTIO_NET_F_GUEST_UFO))
> +	if (virtnet_check_guest_gso(vi))
>   		vi->big_packets = true;
>   
>   	if (virtio_has_feature(vdev, VIRTIO_NET_F_MRG_RXBUF))


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[virtio-dev] [PATCH v3 2/2] virtio-net: use mtu size as buffer length for big packets

[Gavin Li]

Currently add_recvbuf_big() allocates MAX_SKB_FRAGS segments for big
packets even when GUEST_* offloads are not present on the device.
However, if guest GSO is not supported, it would be sufficient to
allocate segments to cover just up the MTU size and no further.
Allocating the maximum amount of segments results in a large waste of
buffer space in the queue, which limits the number of packets that can
be buffered and can result in reduced performance.

Therefore, if guest GSO is not supported, use the MTU to calculate the
optimal amount of segments required.

When guest offload is enabled at runtime, RQ already has packets of bytes
less than 64K. So when packet of 64KB arrives, all the packets of such
size will be dropped. and RQ is now not usable.

So this means that during set_guest_offloads() phase, RQs have to be
destroyed and recreated, which requires almost driver reload.

If VIRTIO_NET_F_CTRL_GUEST_OFFLOADS has been negotiated, then it should
always treat them as GSO enabled.

Below is the iperf TCP test results over a Mellanox NIC, using vDPA for
1 VQ, queue size 1024, before and after the change, with the iperf
server running over the virtio-net interface.

MTU(Bytes)/Bandwidth (Gbit/s)
             Before   After
  1500        22.5     22.4
  9000        12.8     25.9

Signed-off-by: Gavin Li <gavinl@nvidia.com>
Reviewed-by: Gavi Teitz <gavi@nvidia.com>
Reviewed-by: Parav Pandit <parav@nvidia.com>
---
changelog:
v2->v3
- Addressed comments from Si-Wei
- Simplify the condition check to enable the optimization
v1->v2
- Addressed comments from Jason, Michael, Si-Wei.
- Remove the flag of guest GSO support, set sg_num for big packets and
  use it directly
- Recalculate sg_num for big packets in virtnet_set_guest_offloads
- Replace the round up algorithm with DIV_ROUND_UP
---
 drivers/net/virtio_net.c | 37 ++++++++++++++++++++++++-------------
 1 file changed, 24 insertions(+), 13 deletions(-)

diff --git a/drivers/net/virtio_net.c b/drivers/net/virtio_net.c
index e1904877d461..d2721e71af18 100644
--- a/drivers/net/virtio_net.c
+++ b/drivers/net/virtio_net.c
@@ -225,6 +225,9 @@ struct virtnet_info {
 	/* I like... big packets and I cannot lie! */
 	bool big_packets;
 
+	/* number of sg entries allocated for big packets */
+	unsigned int big_packets_sg_num;
+
 	/* Host will merge rx buffers for big packets (shake it! shake it!) */
 	bool mergeable_rx_bufs;
 
@@ -1331,10 +1334,10 @@ static int add_recvbuf_big(struct virtnet_info *vi, struct receive_queue *rq,
 	char *p;
 	int i, err, offset;
 
-	sg_init_table(rq->sg, MAX_SKB_FRAGS + 2);
+	sg_init_table(rq->sg, vi->big_packets_sg_num + 2);
 
-	/* page in rq->sg[MAX_SKB_FRAGS + 1] is list tail */
-	for (i = MAX_SKB_FRAGS + 1; i > 1; --i) {
+	/* page in rq->sg[vi->big_packets_sg_num + 1] is list tail */
+	for (i = vi->big_packets_sg_num + 1; i > 1; --i) {
 		first = get_a_page(rq, gfp);
 		if (!first) {
 			if (list)
@@ -1365,7 +1368,7 @@ static int add_recvbuf_big(struct virtnet_info *vi, struct receive_queue *rq,
 
 	/* chain first in list head */
 	first->private = (unsigned long)list;
-	err = virtqueue_add_inbuf(rq->vq, rq->sg, MAX_SKB_FRAGS + 2,
+	err = virtqueue_add_inbuf(rq->vq, rq->sg, vi->big_packets_sg_num + 2,
 				  first, gfp);
 	if (err < 0)
 		give_pages(rq, first);
@@ -3690,13 +3693,27 @@ static bool virtnet_check_guest_gso(const struct virtnet_info *vi)
 		virtio_has_feature(vi->vdev, VIRTIO_NET_F_GUEST_UFO));
 }
 
+static void virtnet_set_big_packets_fields(struct virtnet_info *vi, const int mtu)
+{
+	bool guest_gso = virtnet_check_guest_gso(vi);
+
+	/* If device can receive ANY guest GSO packets, regardless of mtu,
+	 * allocate packets of maximum size, otherwise limit it to only
+	 * mtu size worth only.
+	 */
+	if (mtu > ETH_DATA_LEN || guest_gso) {
+		vi->big_packets = true;
+		vi->big_packets_sg_num = guest_gso ? MAX_SKB_FRAGS : DIV_ROUND_UP(mtu, PAGE_SIZE);
+	}
+}
+
 static int virtnet_probe(struct virtio_device *vdev)
 {
 	int i, err = -ENOMEM;
 	struct net_device *dev;
 	struct virtnet_info *vi;
 	u16 max_queue_pairs;
-	int mtu;
+	int mtu = 0;
 
 	/* Find if host supports multiqueue/rss virtio_net device */
 	max_queue_pairs = 1;
@@ -3784,10 +3801,6 @@ static int virtnet_probe(struct virtio_device *vdev)
 	INIT_WORK(&vi->config_work, virtnet_config_changed_work);
 	spin_lock_init(&vi->refill_lock);
 
-	/* If we can receive ANY GSO packets, we must allocate large ones. */
-	if (virtnet_check_guest_gso(vi))
-		vi->big_packets = true;
-
 	if (virtio_has_feature(vdev, VIRTIO_NET_F_MRG_RXBUF))
 		vi->mergeable_rx_bufs = true;
 
@@ -3853,12 +3866,10 @@ static int virtnet_probe(struct virtio_device *vdev)
 
 		dev->mtu = mtu;
 		dev->max_mtu = mtu;
-
-		/* TODO: size buffers correctly in this case. */
-		if (dev->mtu > ETH_DATA_LEN)
-			vi->big_packets = true;
 	}
 
+	virtnet_set_big_packets_fields(vi, mtu);
+
 	if (vi->any_header_sg)
 		dev->needed_headroom = vi->hdr_len;
 
-- 
2.31.1


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Re: [virtio-dev] [PATCH v3 2/2] virtio-net: use mtu size as buffer length for big packets

[Xuan Zhuo]

On Tue, 30 Aug 2022 05:26:34 +0300, Gavin Li <gavinl@nvidia.com> wrote:
> Currently add_recvbuf_big() allocates MAX_SKB_FRAGS segments for big
> packets even when GUEST_* offloads are not present on the device.
> However, if guest GSO is not supported, it would be sufficient to
> allocate segments to cover just up the MTU size and no further.
> Allocating the maximum amount of segments results in a large waste of
> buffer space in the queue, which limits the number of packets that can
> be buffered and can result in reduced performance.
>
> Therefore, if guest GSO is not supported, use the MTU to calculate the
> optimal amount of segments required.
>
> When guest offload is enabled at runtime, RQ already has packets of bytes
> less than 64K. So when packet of 64KB arrives, all the packets of such
> size will be dropped. and RQ is now not usable.
>
> So this means that during set_guest_offloads() phase, RQs have to be
> destroyed and recreated, which requires almost driver reload.
>
> If VIRTIO_NET_F_CTRL_GUEST_OFFLOADS has been negotiated, then it should
> always treat them as GSO enabled.
>
> Below is the iperf TCP test results over a Mellanox NIC, using vDPA for
> 1 VQ, queue size 1024, before and after the change, with the iperf
> server running over the virtio-net interface.
>
> MTU(Bytes)/Bandwidth (Gbit/s)
>              Before   After
>   1500        22.5     22.4
>   9000        12.8     25.9
>
> Signed-off-by: Gavin Li <gavinl@nvidia.com>
> Reviewed-by: Gavi Teitz <gavi@nvidia.com>
> Reviewed-by: Parav Pandit <parav@nvidia.com>

Reviewed-by: Xuan Zhuo <xuanzhuo@linux.alibaba.com>

> ---
> changelog:
> v2->v3
> - Addressed comments from Si-Wei
> - Simplify the condition check to enable the optimization
> v1->v2
> - Addressed comments from Jason, Michael, Si-Wei.
> - Remove the flag of guest GSO support, set sg_num for big packets and
>   use it directly
> - Recalculate sg_num for big packets in virtnet_set_guest_offloads
> - Replace the round up algorithm with DIV_ROUND_UP
> ---
>  drivers/net/virtio_net.c | 37 ++++++++++++++++++++++++-------------
>  1 file changed, 24 insertions(+), 13 deletions(-)
>
> diff --git a/drivers/net/virtio_net.c b/drivers/net/virtio_net.c
> index e1904877d461..d2721e71af18 100644
> --- a/drivers/net/virtio_net.c
> +++ b/drivers/net/virtio_net.c
> @@ -225,6 +225,9 @@ struct virtnet_info {
>  	/* I like... big packets and I cannot lie! */
>  	bool big_packets;
>
> +	/* number of sg entries allocated for big packets */
> +	unsigned int big_packets_sg_num;
> +
>  	/* Host will merge rx buffers for big packets (shake it! shake it!) */
>  	bool mergeable_rx_bufs;
>
> @@ -1331,10 +1334,10 @@ static int add_recvbuf_big(struct virtnet_info *vi, struct receive_queue *rq,
>  	char *p;
>  	int i, err, offset;
>
> -	sg_init_table(rq->sg, MAX_SKB_FRAGS + 2);
> +	sg_init_table(rq->sg, vi->big_packets_sg_num + 2);
>
> -	/* page in rq->sg[MAX_SKB_FRAGS + 1] is list tail */
> -	for (i = MAX_SKB_FRAGS + 1; i > 1; --i) {
> +	/* page in rq->sg[vi->big_packets_sg_num + 1] is list tail */
> +	for (i = vi->big_packets_sg_num + 1; i > 1; --i) {
>  		first = get_a_page(rq, gfp);
>  		if (!first) {
>  			if (list)
> @@ -1365,7 +1368,7 @@ static int add_recvbuf_big(struct virtnet_info *vi, struct receive_queue *rq,
>
>  	/* chain first in list head */
>  	first->private = (unsigned long)list;
> -	err = virtqueue_add_inbuf(rq->vq, rq->sg, MAX_SKB_FRAGS + 2,
> +	err = virtqueue_add_inbuf(rq->vq, rq->sg, vi->big_packets_sg_num + 2,
>  				  first, gfp);
>  	if (err < 0)
>  		give_pages(rq, first);
> @@ -3690,13 +3693,27 @@ static bool virtnet_check_guest_gso(const struct virtnet_info *vi)
>  		virtio_has_feature(vi->vdev, VIRTIO_NET_F_GUEST_UFO));
>  }
>
> +static void virtnet_set_big_packets_fields(struct virtnet_info *vi, const int mtu)
> +{
> +	bool guest_gso = virtnet_check_guest_gso(vi);
> +
> +	/* If device can receive ANY guest GSO packets, regardless of mtu,
> +	 * allocate packets of maximum size, otherwise limit it to only
> +	 * mtu size worth only.
> +	 */
> +	if (mtu > ETH_DATA_LEN || guest_gso) {
> +		vi->big_packets = true;
> +		vi->big_packets_sg_num = guest_gso ? MAX_SKB_FRAGS : DIV_ROUND_UP(mtu, PAGE_SIZE);
> +	}
> +}
> +
>  static int virtnet_probe(struct virtio_device *vdev)
>  {
>  	int i, err = -ENOMEM;
>  	struct net_device *dev;
>  	struct virtnet_info *vi;
>  	u16 max_queue_pairs;
> -	int mtu;
> +	int mtu = 0;
>
>  	/* Find if host supports multiqueue/rss virtio_net device */
>  	max_queue_pairs = 1;
> @@ -3784,10 +3801,6 @@ static int virtnet_probe(struct virtio_device *vdev)
>  	INIT_WORK(&vi->config_work, virtnet_config_changed_work);
>  	spin_lock_init(&vi->refill_lock);
>
> -	/* If we can receive ANY GSO packets, we must allocate large ones. */
> -	if (virtnet_check_guest_gso(vi))
> -		vi->big_packets = true;
> -
>  	if (virtio_has_feature(vdev, VIRTIO_NET_F_MRG_RXBUF))
>  		vi->mergeable_rx_bufs = true;
>
> @@ -3853,12 +3866,10 @@ static int virtnet_probe(struct virtio_device *vdev)
>
>  		dev->mtu = mtu;
>  		dev->max_mtu = mtu;
> -
> -		/* TODO: size buffers correctly in this case. */
> -		if (dev->mtu > ETH_DATA_LEN)
> -			vi->big_packets = true;
>  	}
>
> +	virtnet_set_big_packets_fields(vi, mtu);
> +
>  	if (vi->any_header_sg)
>  		dev->needed_headroom = vi->hdr_len;
>
> --
> 2.31.1
>
>
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Re: [virtio-dev] [PATCH v3 2/2] virtio-net: use mtu size as buffer length for big packets

[Si-Wei Liu]

On 8/29/2022 7:26 PM, Gavin Li wrote:
> Currently add_recvbuf_big() allocates MAX_SKB_FRAGS segments for big
> packets even when GUEST_* offloads are not present on the device.
> However, if guest GSO is not supported, it would be sufficient to
> allocate segments to cover just up the MTU size and no further.
> Allocating the maximum amount of segments results in a large waste of
> buffer space in the queue, which limits the number of packets that can
> be buffered and can result in reduced performance.
>
> Therefore, if guest GSO is not supported, use the MTU to calculate the
> optimal amount of segments required.
>
> When guest offload is enabled at runtime, RQ already has packets of bytes
> less than 64K. So when packet of 64KB arrives, all the packets of such
> size will be dropped. and RQ is now not usable.
>
> So this means that during set_guest_offloads() phase, RQs have to be
> destroyed and recreated, which requires almost driver reload.
>
> If VIRTIO_NET_F_CTRL_GUEST_OFFLOADS has been negotiated, then it should
> always treat them as GSO enabled.
>
> Below is the iperf TCP test results over a Mellanox NIC, using vDPA for
> 1 VQ, queue size 1024, before and after the change, with the iperf
> server running over the virtio-net interface.
>
> MTU(Bytes)/Bandwidth (Gbit/s)
>               Before   After
>    1500        22.5     22.4
>    9000        12.8     25.9
>
> Signed-off-by: Gavin Li <gavinl@nvidia.com>
> Reviewed-by: Gavi Teitz <gavi@nvidia.com>
> Reviewed-by: Parav Pandit <parav@nvidia.com>
> ---
> changelog:
> v2->v3
> - Addressed comments from Si-Wei
> - Simplify the condition check to enable the optimization
> v1->v2
> - Addressed comments from Jason, Michael, Si-Wei.
> - Remove the flag of guest GSO support, set sg_num for big packets and
>    use it directly
> - Recalculate sg_num for big packets in virtnet_set_guest_offloads
> - Replace the round up algorithm with DIV_ROUND_UP
> ---
>   drivers/net/virtio_net.c | 37 ++++++++++++++++++++++++-------------
>   1 file changed, 24 insertions(+), 13 deletions(-)
>
> diff --git a/drivers/net/virtio_net.c b/drivers/net/virtio_net.c
> index e1904877d461..d2721e71af18 100644
> --- a/drivers/net/virtio_net.c
> +++ b/drivers/net/virtio_net.c
> @@ -225,6 +225,9 @@ struct virtnet_info {
>   	/* I like... big packets and I cannot lie! */
>   	bool big_packets;
>   
> +	/* number of sg entries allocated for big packets */
> +	unsigned int big_packets_sg_num;
Sorry for nit picking, but in my opinion big_packets_num_skbfrags might 
be a better name than big_packets_sg_num, where the comment could be 
written as "number of skb fragments for big packets" rather than "number 
of sg entries allocated for big packets".

Reviewed-by: Si-Wei Liu <si-wei.liu@oracle.com>

> +
>   	/* Host will merge rx buffers for big packets (shake it! shake it!) */
>   	bool mergeable_rx_bufs;
>   
> @@ -1331,10 +1334,10 @@ static int add_recvbuf_big(struct virtnet_info *vi, struct receive_queue *rq,
>   	char *p;
>   	int i, err, offset;
>   
> -	sg_init_table(rq->sg, MAX_SKB_FRAGS + 2);
> +	sg_init_table(rq->sg, vi->big_packets_sg_num + 2);
>   
> -	/* page in rq->sg[MAX_SKB_FRAGS + 1] is list tail */
> -	for (i = MAX_SKB_FRAGS + 1; i > 1; --i) {
> +	/* page in rq->sg[vi->big_packets_sg_num + 1] is list tail */
> +	for (i = vi->big_packets_sg_num + 1; i > 1; --i) {
>   		first = get_a_page(rq, gfp);
>   		if (!first) {
>   			if (list)
> @@ -1365,7 +1368,7 @@ static int add_recvbuf_big(struct virtnet_info *vi, struct receive_queue *rq,
>   
>   	/* chain first in list head */
>   	first->private = (unsigned long)list;
> -	err = virtqueue_add_inbuf(rq->vq, rq->sg, MAX_SKB_FRAGS + 2,
> +	err = virtqueue_add_inbuf(rq->vq, rq->sg, vi->big_packets_sg_num + 2,
>   				  first, gfp);
>   	if (err < 0)
>   		give_pages(rq, first);
> @@ -3690,13 +3693,27 @@ static bool virtnet_check_guest_gso(const struct virtnet_info *vi)
>   		virtio_has_feature(vi->vdev, VIRTIO_NET_F_GUEST_UFO));
>   }
>   
> +static void virtnet_set_big_packets_fields(struct virtnet_info *vi, const int mtu)
> +{
> +	bool guest_gso = virtnet_check_guest_gso(vi);
> +
> +	/* If device can receive ANY guest GSO packets, regardless of mtu,
> +	 * allocate packets of maximum size, otherwise limit it to only
> +	 * mtu size worth only.
> +	 */
> +	if (mtu > ETH_DATA_LEN || guest_gso) {
> +		vi->big_packets = true;
> +		vi->big_packets_sg_num = guest_gso ? MAX_SKB_FRAGS : DIV_ROUND_UP(mtu, PAGE_SIZE);
> +	}
> +}
> +
>   static int virtnet_probe(struct virtio_device *vdev)
>   {
>   	int i, err = -ENOMEM;
>   	struct net_device *dev;
>   	struct virtnet_info *vi;
>   	u16 max_queue_pairs;
> -	int mtu;
> +	int mtu = 0;
>   
>   	/* Find if host supports multiqueue/rss virtio_net device */
>   	max_queue_pairs = 1;
> @@ -3784,10 +3801,6 @@ static int virtnet_probe(struct virtio_device *vdev)
>   	INIT_WORK(&vi->config_work, virtnet_config_changed_work);
>   	spin_lock_init(&vi->refill_lock);
>   
> -	/* If we can receive ANY GSO packets, we must allocate large ones. */
> -	if (virtnet_check_guest_gso(vi))
> -		vi->big_packets = true;
> -
>   	if (virtio_has_feature(vdev, VIRTIO_NET_F_MRG_RXBUF))
>   		vi->mergeable_rx_bufs = true;
>   
> @@ -3853,12 +3866,10 @@ static int virtnet_probe(struct virtio_device *vdev)
>   
>   		dev->mtu = mtu;
>   		dev->max_mtu = mtu;
> -
> -		/* TODO: size buffers correctly in this case. */
> -		if (dev->mtu > ETH_DATA_LEN)
> -			vi->big_packets = true;
>   	}
>   
> +	virtnet_set_big_packets_fields(vi, mtu);
> +
>   	if (vi->any_header_sg)
>   		dev->needed_headroom = vi->hdr_len;
>   


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Re: [virtio-dev] [PATCH v3 2/2] virtio-net: use mtu size as buffer length for big packets

[Gavin Li]

On 8/31/2022 4:33 PM, Si-Wei Liu wrote:
> External email: Use caution opening links or attachments
>
>
> On 8/29/2022 7:26 PM, Gavin Li wrote:
>> Currently add_recvbuf_big() allocates MAX_SKB_FRAGS segments for big
>> packets even when GUEST_* offloads are not present on the device.
>> However, if guest GSO is not supported, it would be sufficient to
>> allocate segments to cover just up the MTU size and no further.
>> Allocating the maximum amount of segments results in a large waste of
>> buffer space in the queue, which limits the number of packets that can
>> be buffered and can result in reduced performance.
>>
>> Therefore, if guest GSO is not supported, use the MTU to calculate the
>> optimal amount of segments required.
>>
>> When guest offload is enabled at runtime, RQ already has packets of 
>> bytes
>> less than 64K. So when packet of 64KB arrives, all the packets of such
>> size will be dropped. and RQ is now not usable.
>>
>> So this means that during set_guest_offloads() phase, RQs have to be
>> destroyed and recreated, which requires almost driver reload.
>>
>> If VIRTIO_NET_F_CTRL_GUEST_OFFLOADS has been negotiated, then it should
>> always treat them as GSO enabled.
>>
>> Below is the iperf TCP test results over a Mellanox NIC, using vDPA for
>> 1 VQ, queue size 1024, before and after the change, with the iperf
>> server running over the virtio-net interface.
>>
>> MTU(Bytes)/Bandwidth (Gbit/s)
>>               Before   After
>>    1500        22.5     22.4
>>    9000        12.8     25.9
>>
>> Signed-off-by: Gavin Li <gavinl@nvidia.com>
>> Reviewed-by: Gavi Teitz <gavi@nvidia.com>
>> Reviewed-by: Parav Pandit <parav@nvidia.com>
>> ---
>> changelog:
>> v2->v3
>> - Addressed comments from Si-Wei
>> - Simplify the condition check to enable the optimization
>> v1->v2
>> - Addressed comments from Jason, Michael, Si-Wei.
>> - Remove the flag of guest GSO support, set sg_num for big packets and
>>    use it directly
>> - Recalculate sg_num for big packets in virtnet_set_guest_offloads
>> - Replace the round up algorithm with DIV_ROUND_UP
>> ---
>>   drivers/net/virtio_net.c | 37 ++++++++++++++++++++++++-------------
>>   1 file changed, 24 insertions(+), 13 deletions(-)
>>
>> diff --git a/drivers/net/virtio_net.c b/drivers/net/virtio_net.c
>> index e1904877d461..d2721e71af18 100644
>> --- a/drivers/net/virtio_net.c
>> +++ b/drivers/net/virtio_net.c
>> @@ -225,6 +225,9 @@ struct virtnet_info {
>>       /* I like... big packets and I cannot lie! */
>>       bool big_packets;
>>
>> +     /* number of sg entries allocated for big packets */
>> +     unsigned int big_packets_sg_num;
> Sorry for nit picking, but in my opinion big_packets_num_skbfrags might
> be a better name than big_packets_sg_num, where the comment could be
> written as "number of skb fragments for big packets" rather than "number
> of sg entries allocated for big packets".
ACK
>
> Reviewed-by: Si-Wei Liu <si-wei.liu@oracle.com>
>
>> +
>>       /* Host will merge rx buffers for big packets (shake it! shake 
>> it!) */
>>       bool mergeable_rx_bufs;
>>
>> @@ -1331,10 +1334,10 @@ static int add_recvbuf_big(struct 
>> virtnet_info *vi, struct receive_queue *rq,
>>       char *p;
>>       int i, err, offset;
>>
>> -     sg_init_table(rq->sg, MAX_SKB_FRAGS + 2);
>> +     sg_init_table(rq->sg, vi->big_packets_sg_num + 2);
>>
>> -     /* page in rq->sg[MAX_SKB_FRAGS + 1] is list tail */
>> -     for (i = MAX_SKB_FRAGS + 1; i > 1; --i) {
>> +     /* page in rq->sg[vi->big_packets_sg_num + 1] is list tail */
>> +     for (i = vi->big_packets_sg_num + 1; i > 1; --i) {
>>               first = get_a_page(rq, gfp);
>>               if (!first) {
>>                       if (list)
>> @@ -1365,7 +1368,7 @@ static int add_recvbuf_big(struct virtnet_info 
>> *vi, struct receive_queue *rq,
>>
>>       /* chain first in list head */
>>       first->private = (unsigned long)list;
>> -     err = virtqueue_add_inbuf(rq->vq, rq->sg, MAX_SKB_FRAGS + 2,
>> +     err = virtqueue_add_inbuf(rq->vq, rq->sg, 
>> vi->big_packets_sg_num + 2,
>>                                 first, gfp);
>>       if (err < 0)
>>               give_pages(rq, first);
>> @@ -3690,13 +3693,27 @@ static bool virtnet_check_guest_gso(const 
>> struct virtnet_info *vi)
>>               virtio_has_feature(vi->vdev, VIRTIO_NET_F_GUEST_UFO));
>>   }
>>
>> +static void virtnet_set_big_packets_fields(struct virtnet_info *vi, 
>> const int mtu)
>> +{
>> +     bool guest_gso = virtnet_check_guest_gso(vi);
>> +
>> +     /* If device can receive ANY guest GSO packets, regardless of mtu,
>> +      * allocate packets of maximum size, otherwise limit it to only
>> +      * mtu size worth only.
>> +      */
>> +     if (mtu > ETH_DATA_LEN || guest_gso) {
>> +             vi->big_packets = true;
>> +             vi->big_packets_sg_num = guest_gso ? MAX_SKB_FRAGS : 
>> DIV_ROUND_UP(mtu, PAGE_SIZE);
>> +     }
>> +}
>> +
>>   static int virtnet_probe(struct virtio_device *vdev)
>>   {
>>       int i, err = -ENOMEM;
>>       struct net_device *dev;
>>       struct virtnet_info *vi;
>>       u16 max_queue_pairs;
>> -     int mtu;
>> +     int mtu = 0;
>>
>>       /* Find if host supports multiqueue/rss virtio_net device */
>>       max_queue_pairs = 1;
>> @@ -3784,10 +3801,6 @@ static int virtnet_probe(struct virtio_device 
>> *vdev)
>>       INIT_WORK(&vi->config_work, virtnet_config_changed_work);
>>       spin_lock_init(&vi->refill_lock);
>>
>> -     /* If we can receive ANY GSO packets, we must allocate large 
>> ones. */
>> -     if (virtnet_check_guest_gso(vi))
>> -             vi->big_packets = true;
>> -
>>       if (virtio_has_feature(vdev, VIRTIO_NET_F_MRG_RXBUF))
>>               vi->mergeable_rx_bufs = true;
>>
>> @@ -3853,12 +3866,10 @@ static int virtnet_probe(struct virtio_device 
>> *vdev)
>>
>>               dev->mtu = mtu;
>>               dev->max_mtu = mtu;
>> -
>> -             /* TODO: size buffers correctly in this case. */
>> -             if (dev->mtu > ETH_DATA_LEN)
>> -                     vi->big_packets = true;
>>       }
>>
>> +     virtnet_set_big_packets_fields(vi, mtu);
>> +
>>       if (vi->any_header_sg)
>>               dev->needed_headroom = vi->hdr_len;
>>
>

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