Si-Wei Liu
2022-Aug-05 22:11 UTC
[virtio-dev] [PATCH] virtio-net: use mtu size as buffer length for big packets
On 8/1/2022 9:45 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 GSO is not supported,GUEST GSO (virtio term), or GRO HW (netdev core term) it should have been be called.> 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 GSO is not supported,Ditto.> use the MTU to calculate the > optimal amount of segments required. > > 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 at nvidia.com> > Reviewed-by: Gavi Teitz <gavi at nvidia.com> > Reviewed-by: Parav Pandit <parav at nvidia.com> > --- > drivers/net/virtio_net.c | 20 ++++++++++++++++---- > 1 file changed, 16 insertions(+), 4 deletions(-) > > diff --git a/drivers/net/virtio_net.c b/drivers/net/virtio_net.c > index ec8e1b3108c3..d36918c1809d 100644 > --- a/drivers/net/virtio_net.c > +++ b/drivers/net/virtio_net.c > @@ -222,6 +222,9 @@ struct virtnet_info { > /* I like... big packets and I cannot lie! */ > bool big_packets; > > + /* Indicates GSO support */ > + bool gso_is_supported; > + > /* Host will merge rx buffers for big packets (shake it! shake it!) */ > bool mergeable_rx_bufs; > > @@ -1312,14 +1315,21 @@ static int add_recvbuf_small(struct virtnet_info *vi, struct receive_queue *rq, > static int add_recvbuf_big(struct virtnet_info *vi, struct receive_queue *rq, > gfp_t gfp) > { > + unsigned int sg_num = MAX_SKB_FRAGS; > struct page *first, *list = NULL; > char *p; > int i, err, offset; > > - sg_init_table(rq->sg, MAX_SKB_FRAGS + 2); > + if (!vi->gso_is_supported) { > + unsigned int mtu = vi->dev->mtu; > + > + sg_num = (mtu % PAGE_SIZE) ? mtu / PAGE_SIZE + 1 : mtu / PAGE_SIZE;DIV_ROUND_UP() can be used? Since this branch slightly adds up cost to the datapath, I wonder if this sg_num can be saved and set only once (generally in virtnet_probe time) in struct virtnet_info?> + } > + > + sg_init_table(rq->sg, sg_num + 2); > > /* page in rq->sg[MAX_SKB_FRAGS + 1] is list tail */Comment doesn't match code.> - for (i = MAX_SKB_FRAGS + 1; i > 1; --i) { > + for (i = sg_num + 1; i > 1; --i) { > first = get_a_page(rq, gfp); > if (!first) { > if (list) > @@ -1350,7 +1360,7 @@ 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, sg_num + 2, > first, gfp); > if (err < 0) > give_pages(rq, first); > @@ -3571,8 +3581,10 @@ static int virtnet_probe(struct virtio_device *vdev) > 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)) > + virtio_has_feature(vdev, VIRTIO_NET_F_GUEST_UFO)) { > vi->big_packets = true; > + vi->gso_is_supported = true;Please do the same for virtnet_clear_guest_offloads(), and correspondingly virtnet_restore_guest_offloads() as well. Not sure why virtnet_clear_guest_offloads() or the caller doesn't unset big_packet on successful return, seems like a bug to me. Thanks, -Siwei> + } > > if (virtio_has_feature(vdev, VIRTIO_NET_F_MRG_RXBUF)) > vi->mergeable_rx_bufs = true;
Si-Wei Liu
2022-Aug-05 23:26 UTC
[virtio-dev] [PATCH] virtio-net: use mtu size as buffer length for big packets
On 8/5/2022 3:11 PM, Si-Wei Liu wrote:> > > On 8/1/2022 9:45 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 GSO is not supported, > GUEST GSO (virtio term), or GRO HW (netdev core term) it should have > been be called. > >> ? 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 GSO is not supported, > Ditto. > >> use the MTU to calculate the >> optimal amount of segments required. >> >> 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 at nvidia.com> >> Reviewed-by: Gavi Teitz <gavi at nvidia.com> >> Reviewed-by: Parav Pandit <parav at nvidia.com> >> --- >> ? drivers/net/virtio_net.c | 20 ++++++++++++++++---- >> ? 1 file changed, 16 insertions(+), 4 deletions(-) >> >> diff --git a/drivers/net/virtio_net.c b/drivers/net/virtio_net.c >> index ec8e1b3108c3..d36918c1809d 100644 >> --- a/drivers/net/virtio_net.c >> +++ b/drivers/net/virtio_net.c >> @@ -222,6 +222,9 @@ struct virtnet_info { >> ????? /* I like... big packets and I cannot lie! */ >> ????? bool big_packets; >> ? +??? /* Indicates GSO support */ >> +??? bool gso_is_supported; >> + >> ????? /* Host will merge rx buffers for big packets (shake it! shake >> it!) */ >> ????? bool mergeable_rx_bufs; >> ? @@ -1312,14 +1315,21 @@ static int add_recvbuf_small(struct >> virtnet_info *vi, struct receive_queue *rq, >> ? static int add_recvbuf_big(struct virtnet_info *vi, struct >> receive_queue *rq, >> ???????????????? gfp_t gfp) >> ? { >> +??? unsigned int sg_num = MAX_SKB_FRAGS; >> ????? struct page *first, *list = NULL; >> ????? char *p; >> ????? int i, err, offset; >> ? -??? sg_init_table(rq->sg, MAX_SKB_FRAGS + 2); >> +??? if (!vi->gso_is_supported) { >> +??????? unsigned int mtu = vi->dev->mtu; >> + >> +??????? sg_num = (mtu % PAGE_SIZE) ? mtu / PAGE_SIZE + 1 : mtu / >> PAGE_SIZE; > DIV_ROUND_UP() can be used? > > Since this branch slightly adds up cost to the datapath, I wonder if > this sg_num can be saved and set only once (generally in virtnet_probe > time... , but can align with new mtu during .ndo_change_mtu(), too.> ) in struct virtnet_info?Thanks, -Siwei>> +??? } >> + >> +??? sg_init_table(rq->sg, sg_num + 2); >> ? ????? /* page in rq->sg[MAX_SKB_FRAGS + 1] is list tail */ > Comment doesn't match code. >> -??? for (i = MAX_SKB_FRAGS + 1; i > 1; --i) { >> +??? for (i = sg_num + 1; i > 1; --i) { >> ????????? first = get_a_page(rq, gfp); >> ????????? if (!first) { >> ????????????? if (list) >> @@ -1350,7 +1360,7 @@ 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, sg_num + 2, >> ??????????????????? first, gfp); >> ????? if (err < 0) >> ????????? give_pages(rq, first); >> @@ -3571,8 +3581,10 @@ static int virtnet_probe(struct virtio_device >> *vdev) >> ????? 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)) >> +??????? virtio_has_feature(vdev, VIRTIO_NET_F_GUEST_UFO)) { >> ????????? vi->big_packets = true; >> +??????? vi->gso_is_supported = true; > Please do the same for virtnet_clear_guest_offloads(), and > correspondingly virtnet_restore_guest_offloads() as well. Not sure why > virtnet_clear_guest_offloads() or the caller doesn't unset big_packet > on successful return, seems like a bug to me. > > > Thanks, > -Siwei >> +??? } >> ? ????? if (virtio_has_feature(vdev, VIRTIO_NET_F_MRG_RXBUF)) >> ????????? vi->mergeable_rx_bufs = true; >