On Tue, Aug 09, 2022 at 11:38:52AM -0700, Si-Wei Liu wrote: > > > On 8/9/2022 12:44 AM, Jason Wang wrote: > > On Tue, Aug 9, 2022 at 3:07 PM Gavin Li <[email protected]> wrote: > > > > > > On 8/9/2022 7:56 AM, Si-Wei Liu wrote: > > > > > > External email: Use caution opening links or attachments > > > > > > > > > On 8/8/2022 12:31 AM, Gavin Li wrote: > > > > > > > > > On 8/6/2022 6:11 AM, Si-Wei Liu wrote: > > > > > > External email: Use caution opening links or attachments > > > > > > > > > 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. > > > > > > ACK > > > > > > > > > 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. > > > > > > ACK > > > > > > > > > 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 <[email protected]> > > > Reviewed-by: Gavi Teitz <[email protected]> > > > Reviewed-by: Parav Pandit <[email protected]> > > > --- > > > 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? > > > > > > ACK > > > > > > > > > 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? > > > > > > Not sure how to do it and align it with align with new mtu during > > > .ndo_change_mtu()---as you mentioned in the following mail. Any idea? > > > ndo_change_mtu might be in vendor specific code and unmanageable. In > > > my case, the mtu can only be changed in the xml of the guest vm. > > > > > > Nope, for e.g. "ip link dev eth0 set mtu 1500" can be done from guest on > > > a virtio-net device with 9000 MTU (as defined in guest xml). Basically > > > guest user can set MTU to any valid value lower than the original > > > HOST_MTU. In the vendor defined .ndo_change_mtu() op, dev_validate_mtu() > > > should have validated the MTU value before coming down to it. And I > > > suspect you might want to do virtnet_close() and virtnet_open() > > > before/after changing the buffer size on the fly (the netif_running() > > > case), implementing .ndo_change_mtu() will be needed anyway. > > > > > > a guest VM driver changing mtu to smaller one is valid use case. However, > > > current optimization suggested in the patch doesn't degrade any > > > performance. Performing close() and open() sequence is good idea, that I > > > would like to take up next after this patch as its going to be more than > > > one patch to achieve it. > > Right, it could be done on top. > > > > But another note is that, it would still be better to support GUEST GSO > > feature: > > > > 1) can work for the case for path MTU > > 2) (migration)compatibility with software backends > > > > > > > > + } > > > + > > > + sg_init_table(rq->sg, sg_num + 2); > > > > > > /* page in rq->sg[MAX_SKB_FRAGS + 1] is list tail */ > > > > > > Comment doesn't match code. > > > > > > ACK > > > > > > - 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. > > It is fine as long as > > > > 1) we don't implement ethtool API for changing guest offloads > Not sure if I missed something, but it looks the current > virtnet_set_features() already supports toggling on/off GRO HW through > commit a02e8964eaf9271a8a5fcc0c55bd13f933bafc56 (formerly misnamed as LRO). > Sorry, I realized I had a typo in email: "virtnet_set_guest_offloads() or > the caller doesn't unset big_packet ...".
"we" here is the device, not the driver. > > 2) big mode XDP is not enabled > Currently it is not. Not a single patch nor this patch, but the context for > the eventual goal is to allow XDP on a MTU=9000 link when guest users > intentionally lower down MTU to 1500. > > Regards, > -Siwei > > > > So that code works only for XDP but we forbid big packets in the case > > of XDP right now. > > > > Thanks > > > > > ACK. The two calls virtnet_set_guest_offloads and > > > virtnet_set_guest_offloads is also called by virtnet_set_features. Do > > > you think if I can do this in virtnet_set_guest_offloads? > > > > > > I think that it should be fine, though you may want to deal with the XDP > > > path not to regress it. > > > > > > -Siwei > > > > > > > > > > > > Thanks, > > > -Siwei > > > > > > + } > > > > > > if (virtio_has_feature(vdev, VIRTIO_NET_F_MRG_RXBUF)) > > > vi->mergeable_rx_bufs = true; > > > > > > > > > _______________________________________________ Virtualization mailing list [email protected] https://lists.linuxfoundation.org/mailman/listinfo/virtualization
