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Fri, 16 Oct 2026 07:33:47 -0700 (PDT) Date: Fri, 16 Oct 2026 16:33:44 +0200 From: Stefano Garzarella To: Jia Jia Cc: stefanha@redhat.com, mst@redhat.com, jasowangio@gmail.com, eperezma@redhat.com, xuanzhuo@linux.alibaba.com, davem@davemloft.net, edumazet@kernel.org, kuba@kernel.org, pabeni@redhat.com, horms@kernel.org, virtualization@lists.linux.dev, kvm@vger.kernel.org, netdev@vger.kernel.org, linux-kernel@vger.kernel.org, bobbyeshleman@gmail.com Subject: Re: [PATCH net-next v4 2/4] vsock/virtio: amortize RX socket locking for stream packets Message-ID: References: <20261014115640.184286-1-physicalmtea@gmail.com> <20261014115640.184286-3-physicalmtea@gmail.com> Precedence: bulk X-Mailing-List: virtualization@lists.linux.dev List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 In-Reply-To: <20261014115640.184286-3-physicalmtea@gmail.com> X-Mimecast-Spam-Score: 0 X-Mimecast-MFC-PROC-ID: 0kOP6xf72FuzvtTvBpaqt_J861MaIZOQKQ4h1BXX6Wc_1792161229 X-Mimecast-Originator: redhat.com Content-Type: text/plain; charset=us-ascii; format=flowed Content-Disposition: inline On Wed, Oct 14, 2026 at 07:56:38PM +0800, Jia Jia wrote: >The virtio-vsock RX worker currently looks up the socket and takes its >lock for every packet. Keep the socket lock and lookup reference across a >bounded run of STREAM/RW packets for the same established socket. > >Reuse the locked socket while packets continue to match the same flow. >End the batch for a different flow, non-RW traffic, malformed packets, or >a change in socket state, transport, protocol, or receive-buffer headroom. >A connected-table miss uses the existing receive path. > >The reused path still traces every packet, takes an skb owner reference, >validates the source and transport, updates credit, and runs the existing >receive state machine. > >Sockmap can replace the protocol without taking the socket lock. Check the >psock marker at each packet boundary and serialize initial admission with >sk_callback_lock, so a concurrent attach ends batching at the next packet. > >Cap a batch at 64 packets and 64K of payload. The packet limit bounds Why this cap? >per-packet work, while the byte limit bounds how much data can queue before >a reader acquires the socket lock. Batching remains in the process-context >RX worker. IMHO this patch should carry performance results. > >Signed-off-by: Jia Jia >--- > include/linux/virtio_vsock.h | 11 ++ > net/vmw_vsock/virtio_transport.c | 29 +++- Why no changes in vhost-vsock or vsock_loopback? I'm not asking to do that, I'd like to understand why only in the driver. > net/vmw_vsock/virtio_transport_common.c | 183 +++++++++++++++++++++++- > 3 files changed, 216 insertions(+), 7 deletions(-) > >diff --git a/include/linux/virtio_vsock.h b/include/linux/virtio_vsock.h >index f91704731057e..26dde6909c4ed 100644 >--- a/include/linux/virtio_vsock.h >+++ b/include/linux/virtio_vsock.h >@@ -282,6 +282,17 @@ void virtio_transport_destruct(struct vsock_sock *vsk); > > void virtio_transport_recv_pkt(struct virtio_transport *t, > struct sk_buff *skb, struct net *net); >+ >+struct virtio_transport_rx_batch { >+ struct sock *sk; >+ unsigned int pkts; >+ size_t bytes; >+}; >+ >+void virtio_transport_recv_pkt_batch(struct virtio_transport *t, >+ struct sk_buff *skb, struct net *net, >+ struct virtio_transport_rx_batch *batch); >+void virtio_transport_rx_batch_finish(struct virtio_transport_rx_batch *batch); > void virtio_transport_inc_tx_pkt(struct virtio_vsock_sock *vvs, struct sk_buff *skb); > u32 virtio_transport_get_credit(struct virtio_vsock_sock *vvs, u32 wanted); > void virtio_transport_put_credit(struct virtio_vsock_sock *vvs, u32 credit); >diff --git a/net/vmw_vsock/virtio_transport.c b/net/vmw_vsock/virtio_transport.c >index 4f9aa9c4c3aa5..ef076732158d4 100644 >--- a/net/vmw_vsock/virtio_transport.c >+++ b/net/vmw_vsock/virtio_transport.c >@@ -629,8 +629,16 @@ virtio_transport_seqpacket_allow(struct vsock_sock *vsk, u32 remote_cid) > return seqpacket_allow; > } > >+/* >+ * Keep a bounded run of packets for one socket under a single socket lock. >+ * Limit packet count and payload size to bound the work done while locked. Here we should explain why we choose these values. >+ */ >+#define VIRTIO_TRANSPORT_RX_BATCH_MAX_PKTS 64 >+#define VIRTIO_TRANSPORT_RX_BATCH_MAX_BYTES (64 * 1024) >+ > static void virtio_transport_rx_work(struct work_struct *work) > { >+ struct virtio_transport_rx_batch batch = {}; > struct virtio_vsock *vsock = > container_of(work, struct virtio_vsock, rx_work); > struct virtqueue *vq; >@@ -666,6 +674,7 @@ static void virtio_transport_rx_work(struct work_struct *work) > /* Drop short/long packets */ > if (unlikely(len < sizeof(*hdr) || > len > virtio_vsock_skb_len(skb))) { >+ virtio_transport_rx_batch_finish(&batch); > kfree_skb(skb); > continue; > } >@@ -673,6 +682,7 @@ static void virtio_transport_rx_work(struct work_struct *work) > hdr = virtio_vsock_hdr(skb); > payload_len = le32_to_cpu(hdr->len); > if (unlikely(payload_len > len - sizeof(*hdr))) { >+ virtio_transport_rx_batch_finish(&batch); > kfree_skb(skb); > continue; > } >@@ -680,16 +690,33 @@ static void virtio_transport_rx_work(struct work_struct *work) > if (payload_len) > virtio_vsock_skb_put(skb, payload_len); > >+ if (batch.sk && >+ payload_len > VIRTIO_TRANSPORT_RX_BATCH_MAX_BYTES - >+ batch.bytes) { Why this? >+ virtio_transport_rx_batch_finish(&batch); >+ } >+ > virtio_transport_deliver_tap_pkt(skb); > > /* Force virtio-transport into global mode since it > * does not yet support local-mode namespacing. > */ >- virtio_transport_recv_pkt(&virtio_transport, skb, NULL); >+ virtio_transport_recv_pkt_batch(&virtio_transport, skb, NULL, >+ &batch); >+ >+ if (batch.sk) { >+ batch.pkts++; >+ batch.bytes += payload_len; >+ if (batch.pkts >= VIRTIO_TRANSPORT_RX_BATCH_MAX_PKTS || >+ batch.bytes >= VIRTIO_TRANSPORT_RX_BATCH_MAX_BYTES) { >+ virtio_transport_rx_batch_finish(&batch); >+ } >+ } Why this is not in the common part? > } > } while (!virtqueue_enable_cb(vq)); > > out: >+ virtio_transport_rx_batch_finish(&batch); > if (vsock->rx_buf_nr < vsock->rx_buf_max_nr / 2) > virtio_vsock_rx_fill(vsock); > out_nofill: >diff --git a/net/vmw_vsock/virtio_transport_common.c b/net/vmw_vsock/virtio_transport_common.c >index 61ee3bc205d5d..ff74e805527a5 100644 >--- a/net/vmw_vsock/virtio_transport_common.c >+++ b/net/vmw_vsock/virtio_transport_common.c >@@ -576,11 +576,16 @@ virtio_transport_collapse_rx_queue(struct virtio_vsock_sock *vvs, > skb_queue_splice(&new_queue, &vvs->rx_queue); > } > >+static bool >+virtio_transport_rx_skb_has_headroom(struct virtio_vsock_sock *vvs) >+{ >+ return (u64)(skb_queue_len(&vvs->rx_queue) + 1) * SKB_TRUESIZE(0) <= >+ vvs->buf_alloc; >+} Please move this change in a separate patch. skb_has_headroom() is confusing IMO, maybe virtio_transport_rx_buf_full(), but reversing the return value, so keeping the same check as before. >+ > static bool virtio_transport_inc_rx_pkt(struct virtio_vsock_sock *vvs, > u32 len) > { >- u64 skb_overhead = (skb_queue_len(&vvs->rx_queue) + 1) * SKB_TRUESIZE(0); >- > /* Allow at most buf_alloc * 2 total budget (payload + overhead), > * similar to how SO_RCVBUF is doubled to reserve space for sk_buff > * metadata. Check payload against buf_alloc to be sure the other >@@ -588,7 +593,7 @@ static bool virtio_transport_inc_rx_pkt(struct virtio_vsock_sock *vvs, > * queue growth. > */ > if ((u64)vvs->buf_used + len > vvs->buf_alloc || >- skb_overhead > vvs->buf_alloc) >+ !virtio_transport_rx_skb_has_headroom(vvs)) > return false; > > vvs->rx_bytes += len; >@@ -1798,12 +1803,38 @@ virtio_transport_find_socket(struct sk_buff *skb, struct sockaddr_vm *src, > return sk; > } > >+static bool >+virtio_transport_sock_has_psock(const struct sock *sk) >+{ >+ return (uintptr_t)rcu_access_pointer(__sk_user_data(sk)) & >+ SK_USER_DATA_PSOCK; >+} >+ >+static bool >+virtio_transport_recv_pkt_batchable(struct virtio_transport *t, >+ struct sock *sk) >+{ >+ struct vsock_sock *vsk = vsock_sk(sk); >+ struct virtio_vsock_sock *vvs = vsk->trans; >+ A comment here to explain why some checks like... >+ return sk->sk_state == TCP_ESTABLISHED && >+ sk->sk_type == SOCK_STREAM && >+ READ_ONCE(sk->sk_prot) == sk->sk_prot_creator && ... this ^ I mean in general to explain better these conditions (I mean not a description of what we are doing, but why we are doing these checks). >+ !sock_flag(sk, SOCK_DONE) && >+ vsk->transport == &t->transport && >+ vvs && virtio_transport_rx_skb_has_headroom(vvs) && >+ !virtio_transport_sock_has_psock(sk); >+} >+ > /* >- * The caller holds sk's socket lock and must free skb if this returns true. >+ * The caller holds sk's socket lock. Set @batchable if the socket can remain >+ * locked for another ordinary STREAM/RW packet. Return true if the caller >+ * must free @skb. > */ > static bool > virtio_transport_recv_pkt_locked(struct virtio_transport *t, >- struct sk_buff *skb, struct sock *sk) >+ struct sk_buff *skb, struct sock *sk, >+ bool *batchable) > { > struct virtio_vsock_hdr *hdr = virtio_vsock_hdr(skb); > struct sockaddr_vm src; >@@ -1813,6 +1844,9 @@ virtio_transport_recv_pkt_locked(struct virtio_transport *t, > vsock_addr_init(&src, le64_to_cpu(hdr->src_cid), > le32_to_cpu(hdr->src_port)); > >+ if (batchable) >+ *batchable = false; >+ > /* Listener sockets accept packets from any source and are not assigned to > * a transport. > */ >@@ -1854,6 +1888,9 @@ virtio_transport_recv_pkt_locked(struct virtio_transport *t, > break; > } > >+ if (batchable) >+ *batchable = virtio_transport_recv_pkt_batchable(t, sk); >+ > return false; > } > >@@ -1894,7 +1931,7 @@ void virtio_transport_recv_pkt(struct virtio_transport *t, > } > > lock_sock(sk); >- free_pkt = virtio_transport_recv_pkt_locked(t, skb, sk); >+ free_pkt = virtio_transport_recv_pkt_locked(t, skb, sk, NULL); > release_sock(sk); > > /* Release refcnt obtained when we fetched this socket out of the >@@ -1910,6 +1947,140 @@ void virtio_transport_recv_pkt(struct virtio_transport *t, > } > EXPORT_SYMBOL_GPL(virtio_transport_recv_pkt); > >+/* >+ * Finish the RX batch. >+ * For a non-empty batch, the caller must hold the socket lock acquired with >+ * lock_sock(). This function releases the lock and the batch's lookup >+ * reference. >+ * An empty batch is a no-op. What empty batch means, I mean how the caller can understand that a batch is empty? Maybe we should provide a function for that... >+ */ >+void virtio_transport_rx_batch_finish(struct virtio_transport_rx_batch *batch) >+{ >+ struct sock *sk = batch->sk; >+ >+ batch->sk = NULL; >+ batch->pkts = 0; >+ batch->bytes = 0; >+ >+ if (!sk) >+ return; >+ >+ release_sock(sk); >+ sock_put(sk); >+} >+EXPORT_SYMBOL_GPL(virtio_transport_rx_batch_finish); >+ >+void virtio_transport_recv_pkt_batch(struct virtio_transport *t, >+ struct sk_buff *skb, struct net *net, >+ struct virtio_transport_rx_batch *batch) >+{ >+ struct virtio_vsock_hdr *hdr = virtio_vsock_hdr(skb); >+ struct sockaddr_vm src, dst; >+ struct vsock_sock *vsk; >+ bool batchable, start_batch; Ditto about declarations order, please check in the entire series. >+ struct sock *sk; >+ bool free_pkt; >+ >+ /* Only STREAM/RW packets can share a socket lock. */ Why? Should the caller holds the lock for the entire batch? Should this be documented? >+ if (le16_to_cpu(hdr->type) != VIRTIO_VSOCK_TYPE_STREAM || >+ le16_to_cpu(hdr->op) != VIRTIO_VSOCK_OP_RW) { >+ virtio_transport_rx_batch_finish(batch); >+ virtio_transport_recv_pkt(t, skb, net); >+ return; >+ } >+ >+ vsock_addr_init(&src, le64_to_cpu(hdr->src_cid), >+ le32_to_cpu(hdr->src_port)); >+ vsock_addr_init(&dst, le64_to_cpu(hdr->dst_cid), >+ le32_to_cpu(hdr->dst_port)); >+ >+ if (batch->sk) { >+ vsk = vsock_sk(batch->sk); >+ if (vsock_addr_equals_addr(&src, &vsk->remote_addr) && >+ dst.svm_port == vsk->local_addr.svm_port && >+ vsock_net_check_mode(sock_net(batch->sk), net) && >+ virtio_transport_recv_pkt_batchable(t, batch->sk)) { >+ sk = batch->sk; >+ trace_virtio_transport_recv_pkt(src.svm_cid, >+ src.svm_port, >+ dst.svm_cid, >+ dst.svm_port, >+ le32_to_cpu(hdr->len), >+ le16_to_cpu(hdr->type), >+ le16_to_cpu(hdr->op), >+ le32_to_cpu(hdr->flags), >+ le32_to_cpu(hdr->buf_alloc), >+ le32_to_cpu(hdr->fwd_cnt)); >+ if (!skb_set_owner_sk_safe(skb, sk)) { >+ WARN_ONCE(1, "receiving vsock socket has sk_refcnt == 0\n"); >+ virtio_transport_rx_batch_finish(batch); >+ kfree_skb(skb); >+ return; >+ } >+ This code is unreadable TBH, there isn't a blank line till here... and too much nested blocks. Maybe you should move this in a function, and use a bit more blank lines. >+ free_pkt = virtio_transport_recv_pkt_locked(t, skb, sk, >+ &batchable); >+ if (!batchable) >+ virtio_transport_rx_batch_finish(batch); >+ if (free_pkt) >+ kfree_skb(skb); >+ return; >+ } >+ >+ virtio_transport_rx_batch_finish(batch); >+ } >+ >+ sk = vsock_find_connected_socket_net(&src, &dst, net); >+ if (!sk) { >+ virtio_transport_recv_pkt(t, skb, net); Why this? >+ return; >+ } >+ >+ if (virtio_transport_get_type(sk) != le16_to_cpu(hdr->type)) { >+ sock_put(sk); >+ virtio_transport_recv_pkt(t, skb, net); >+ return; >+ } >+ >+ trace_virtio_transport_recv_pkt(src.svm_cid, src.svm_port, >+ dst.svm_cid, dst.svm_port, >+ le32_to_cpu(hdr->len), >+ le16_to_cpu(hdr->type), >+ le16_to_cpu(hdr->op), >+ le32_to_cpu(hdr->flags), >+ le32_to_cpu(hdr->buf_alloc), >+ le32_to_cpu(hdr->fwd_cnt)); >+ >+ if (!skb_set_owner_sk_safe(skb, sk)) { >+ WARN_ONCE(1, "receiving vsock socket has sk_refcnt == 0\n"); >+ kfree_skb(skb); >+ return; >+ } We have this code duplicated in several place now, can this be avoided? >+ >+ lock_sock(sk); >+ /* >+ * Sockmap removal restores the native protocol under sk_callback_lock. >+ * Serialize this initial eligibility check with that update. >+ */ >+ read_lock_bh(&sk->sk_callback_lock); >+ start_batch = virtio_transport_recv_pkt_batchable(t, sk); >+ read_unlock_bh(&sk->sk_callback_lock); >+ >+ free_pkt = virtio_transport_recv_pkt_locked(t, skb, sk, >+ start_batch ? &batchable : NULL); >+ if (start_batch && batchable) { >+ /* Keep the lookup reference until the batch is released. */ >+ batch->sk = sk; >+ return; >+ } Ah, this is for the first run, when the batch is empty, right? Can you merge in some way both branches? BTW please add some more useful comments (explaining why) >+ >+ release_sock(sk); >+ sock_put(sk); >+ if (free_pkt) >+ kfree_skb(skb); >+} >+EXPORT_SYMBOL_GPL(virtio_transport_recv_pkt_batch); >+ > /* Remove skbs found in a queue that have a vsk that matches. > * > * Each skb is freed. >-- >2.53.0 >