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Message-ID: <20230321082854.jluiqjyc4n5k2vza@sgarzare-redhat> Date: Tue, 21 Mar 2023 09:28:54 +0100 From: Stefano Garzarella <sgarzare@...hat.com> To: Arseniy Krasnov <avkrasnov@...rdevices.ru> Cc: Stefan Hajnoczi <stefanha@...hat.com>, "David S. Miller" <davem@...emloft.net>, Eric Dumazet <edumazet@...gle.com>, Jakub Kicinski <kuba@...nel.org>, Paolo Abeni <pabeni@...hat.com>, Bobby Eshleman <bobby.eshleman@...edance.com>, kvm@...r.kernel.org, virtualization@...ts.linux-foundation.org, netdev@...r.kernel.org, linux-kernel@...r.kernel.org, kernel@...rdevices.ru, oxffffaa@...il.com Subject: Re: [RFC PATCH v2] virtio/vsock: allocate multiple skbuffs on tx On Mon, Mar 20, 2023 at 09:02:19PM +0300, Arseniy Krasnov wrote: > > >On 20.03.2023 17:29, Stefano Garzarella wrote: >> On Sun, Mar 19, 2023 at 09:46:10PM +0300, Arseniy Krasnov wrote: >>> This adds small optimization for tx path: instead of allocating single >>> skbuff on every call to transport, allocate multiple skbuff's until >>> credit space allows, thus trying to send as much as possible data without >>> return to af_vsock.c. >>> >>> Signed-off-by: Arseniy Krasnov <AVKrasnov@...rdevices.ru> >>> --- >>> Link to v1: >>> https://lore.kernel.org/netdev/2c52aa26-8181-d37a-bccd-a86bd3cbc6e1@sberdevices.ru/ >>> >>> Changelog: >>> v1 -> v2: >>> - If sent something, return number of bytes sent (even in >>> case of error). Return error only if failed to sent first >>> skbuff. >>> >>> net/vmw_vsock/virtio_transport_common.c | 53 ++++++++++++++++++------- >>> 1 file changed, 39 insertions(+), 14 deletions(-) >>> >>> diff --git a/net/vmw_vsock/virtio_transport_common.c b/net/vmw_vsock/virtio_transport_common.c >>> index 6564192e7f20..3fdf1433ec28 100644 >>> --- a/net/vmw_vsock/virtio_transport_common.c >>> +++ b/net/vmw_vsock/virtio_transport_common.c >>> @@ -196,7 +196,8 @@ static int virtio_transport_send_pkt_info(struct vsock_sock *vsk, >>> const struct virtio_transport *t_ops; >>> struct virtio_vsock_sock *vvs; >>> u32 pkt_len = info->pkt_len; >>> - struct sk_buff *skb; >>> + u32 rest_len; >>> + int ret; >>> >>> info->type = virtio_transport_get_type(sk_vsock(vsk)); >>> >>> @@ -216,10 +217,6 @@ static int virtio_transport_send_pkt_info(struct vsock_sock *vsk, >>> >>> vvs = vsk->trans; >>> >>> - /* we can send less than pkt_len bytes */ >>> - if (pkt_len > VIRTIO_VSOCK_MAX_PKT_BUF_SIZE) >>> - pkt_len = VIRTIO_VSOCK_MAX_PKT_BUF_SIZE; >>> - >>> /* virtio_transport_get_credit might return less than pkt_len credit */ >>> pkt_len = virtio_transport_get_credit(vvs, pkt_len); >>> >>> @@ -227,17 +224,45 @@ static int virtio_transport_send_pkt_info(struct vsock_sock *vsk, >>> if (pkt_len == 0 && info->op == VIRTIO_VSOCK_OP_RW) >>> return pkt_len; >>> >>> - skb = virtio_transport_alloc_skb(info, pkt_len, >>> - src_cid, src_port, >>> - dst_cid, dst_port); >>> - if (!skb) { >>> - virtio_transport_put_credit(vvs, pkt_len); >>> - return -ENOMEM; >>> - } >>> + ret = 0; >>> + rest_len = pkt_len; >>> + >>> + do { >>> + struct sk_buff *skb; >>> + size_t skb_len; >>> + >>> + skb_len = min_t(u32, VIRTIO_VSOCK_MAX_PKT_BUF_SIZE, rest_len); >>> + >>> + skb = virtio_transport_alloc_skb(info, skb_len, >>> + src_cid, src_port, >>> + dst_cid, dst_port); >>> + if (!skb) { >>> + ret = -ENOMEM; >>> + break; >>> + } >>> + >>> + virtio_transport_inc_tx_pkt(vvs, skb); >>> + >>> + ret = t_ops->send_pkt(skb); >>> + >>> + if (ret < 0) >>> + break; >>> >>> - virtio_transport_inc_tx_pkt(vvs, skb); >>> + rest_len -= skb_len; >> >> t_ops->send_pkt() is returning the number of bytes sent. Current >> implementations always return `skb_len`, so there should be no problem, >> but it would be better to put a comment here, or we should handle the >> case where ret != skb_len to avoid future issues. > >Hello, thanks for review! > >I see. I think i'll handle such partial sends (ret != skb_len) as error, as >it is the only thing to do - we remove 'skb_len' from user's buffer, but >'send_pkt()' returns another value, so it will be strange for me to continue >this tx loop as everything is ok. Something like this: >+ >+ if (ret < 0) >+ break; >+ >+ if (ret != skb_len) { >+ ret = -EFAULT;//or may be -EIO >+ break; >+ } Good for me. > >> >>> + } while (rest_len); >>> >>> - return t_ops->send_pkt(skb); >>> + /* Don't call this function with zero as argument: >>> + * it tries to acquire spinlock and such argument >>> + * makes this call useless. >> >> Good point, can we do the same also for virtio_transport_get_credit()? >> (Maybe in a separate patch) >> >> I'm thinking if may be better to do it directly inside the functions, >> but I don't have a strong opinion on that since we only call them here. >> > >I think in this patch i can call 'virtio_transport_put_credit()' without if, but >i'll prepare separate patch which adds zero argument check to this function. Yep, I agree. >As i see, the only function suitable for such 'if' condition is >'virtio_transport_put_credit()'. Why not even for virtio_transport_get_credit() ? When we send packets without payload (e.g. VIRTIO_VSOCK_OP_REQUEST, VIRTIO_VSOCK_OP_SHUTDOWN) we call virtio_transport_get_credit() with `credit` parameter equal to 0, then we acquire the spinlock but in the end we do nothing. >Anyway - for future use this check won't be bad. Yep, these are minor improvements ;-) Thanks, Stefano
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