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Miller" , Jakub Kicinski Subject: [PATCH net] virtio_net: Do not pull payload in skb->head Date: Fri, 2 Apr 2021 06:26:02 -0700 Message-Id: <20210402132602.3659282-1-eric.dumazet@gmail.com> X-Mailer: git-send-email 2.31.0.208.g409f899ff0-goog MIME-Version: 1.0 Cc: Xuan Zhuo , Eric Dumazet , "Michael S. Tsirkin" , netdev , virtualization@lists.linux-foundation.org, Eric Dumazet X-BeenThere: virtualization@lists.linux-foundation.org X-Mailman-Version: 2.1.15 Precedence: list List-Id: Linux virtualization List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Errors-To: virtualization-bounces@lists.linux-foundation.org Sender: "Virtualization" From: Eric Dumazet Xuan Zhuo reported that commit 3226b158e67c ("net: avoid 32 x truesize under-estimation for tiny skbs") brought a ~10% performance drop. The reason for the performance drop was that GRO was forced to chain sk_buff (using skb_shinfo(skb)->frag_list), which uses more memory but also cause packet consumers to go over a lot of overhead handling all the tiny skbs. It turns out that virtio_net page_to_skb() has a wrong strategy : It allocates skbs with GOOD_COPY_LEN (128) bytes in skb->head, then copies 128 bytes from the page, before feeding the packet to GRO stack. This was suboptimal before commit 3226b158e67c ("net: avoid 32 x truesize under-estimation for tiny skbs") because GRO was using 2 frags per MSS, meaning we were not packing MSS with 100% efficiency. Fix is to pull only the ethernet header in page_to_skb() Then, we change virtio_net_hdr_to_skb() to pull the missing headers, instead of assuming they were already pulled by callers. This fixes the performance regression, but could also allow virtio_net to accept packets with more than 128bytes of headers. Many thanks to Xuan Zhuo for his report, and his tests/help. Fixes: 3226b158e67c ("net: avoid 32 x truesize under-estimation for tiny skbs") Reported-by: Xuan Zhuo Link: https://www.spinics.net/lists/netdev/msg731397.html Co-Developed-by: Xuan Zhuo Signed-off-by: Xuan Zhuo Signed-off-by: Eric Dumazet Cc: "Michael S. Tsirkin" Cc: Jason Wang Cc: virtualization@lists.linux-foundation.org --- drivers/net/virtio_net.c | 10 +++++++--- include/linux/virtio_net.h | 14 +++++++++----- 2 files changed, 16 insertions(+), 8 deletions(-) diff --git a/drivers/net/virtio_net.c b/drivers/net/virtio_net.c index 82e520d2cb1229a0c7b9fd0def3e4a7135536478..0824e6999e49957f7aaf7c990f6259792d42f32b 100644 --- a/drivers/net/virtio_net.c +++ b/drivers/net/virtio_net.c @@ -406,9 +406,13 @@ static struct sk_buff *page_to_skb(struct virtnet_info *vi, offset += hdr_padded_len; p += hdr_padded_len; - copy = len; - if (copy > skb_tailroom(skb)) - copy = skb_tailroom(skb); + /* Copy all frame if it fits skb->head, otherwise + * we let virtio_net_hdr_to_skb() and GRO pull headers as needed. + */ + if (len <= skb_tailroom(skb)) + copy = len; + else + copy = ETH_HLEN + metasize; skb_put_data(skb, p, copy); if (metasize) { diff --git a/include/linux/virtio_net.h b/include/linux/virtio_net.h index 98775d7fa69632e2c2da30b581a666f7fbb94b64..b465f8f3e554f27ced45c35f54f113cf6dce1f07 100644 --- a/include/linux/virtio_net.h +++ b/include/linux/virtio_net.h @@ -65,14 +65,18 @@ static inline int virtio_net_hdr_to_skb(struct sk_buff *skb, skb_reset_mac_header(skb); if (hdr->flags & VIRTIO_NET_HDR_F_NEEDS_CSUM) { - u16 start = __virtio16_to_cpu(little_endian, hdr->csum_start); - u16 off = __virtio16_to_cpu(little_endian, hdr->csum_offset); + u32 start = __virtio16_to_cpu(little_endian, hdr->csum_start); + u32 off = __virtio16_to_cpu(little_endian, hdr->csum_offset); + u32 needed = start + max_t(u32, thlen, off + sizeof(__sum16)); + + if (!pskb_may_pull(skb, needed)) + return -EINVAL; if (!skb_partial_csum_set(skb, start, off)) return -EINVAL; p_off = skb_transport_offset(skb) + thlen; - if (p_off > skb_headlen(skb)) + if (!pskb_may_pull(skb, p_off)) return -EINVAL; } else { /* gso packets without NEEDS_CSUM do not set transport_offset. @@ -102,14 +106,14 @@ static inline int virtio_net_hdr_to_skb(struct sk_buff *skb, } p_off = keys.control.thoff + thlen; - if (p_off > skb_headlen(skb) || + if (!pskb_may_pull(skb, p_off) || keys.basic.ip_proto != ip_proto) return -EINVAL; skb_set_transport_header(skb, keys.control.thoff); } else if (gso_type) { p_off = thlen; - if (p_off > skb_headlen(skb)) + if (!pskb_may_pull(skb, p_off)) return -EINVAL; } } -- 2.31.0.208.g409f899ff0-goog _______________________________________________ Virtualization mailing list Virtualization@lists.linux-foundation.org https://lists.linuxfoundation.org/mailman/listinfo/virtualization From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-15.7 required=3.0 tests=BAYES_00,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,FREEMAIL_FORGED_FROMDOMAIN,FREEMAIL_FROM, HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_CR_TRAILER,INCLUDES_PATCH, MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS,USER_AGENT_GIT autolearn=ham autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id BF171C433B4 for ; Fri, 2 Apr 2021 13:26:10 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 7FAE16113C for ; 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Fri, 02 Apr 2021 06:26:05 -0700 (PDT) From: Eric Dumazet To: "David S . Miller" , Jakub Kicinski Cc: netdev , Eric Dumazet , Eric Dumazet , Xuan Zhuo , "Michael S. Tsirkin" , Jason Wang , virtualization@lists.linux-foundation.org Subject: [PATCH net] virtio_net: Do not pull payload in skb->head Date: Fri, 2 Apr 2021 06:26:02 -0700 Message-Id: <20210402132602.3659282-1-eric.dumazet@gmail.com> X-Mailer: git-send-email 2.31.0.208.g409f899ff0-goog MIME-Version: 1.0 Content-Transfer-Encoding: 8bit Precedence: bulk List-ID: X-Mailing-List: netdev@vger.kernel.org From: Eric Dumazet Xuan Zhuo reported that commit 3226b158e67c ("net: avoid 32 x truesize under-estimation for tiny skbs") brought a ~10% performance drop. The reason for the performance drop was that GRO was forced to chain sk_buff (using skb_shinfo(skb)->frag_list), which uses more memory but also cause packet consumers to go over a lot of overhead handling all the tiny skbs. It turns out that virtio_net page_to_skb() has a wrong strategy : It allocates skbs with GOOD_COPY_LEN (128) bytes in skb->head, then copies 128 bytes from the page, before feeding the packet to GRO stack. This was suboptimal before commit 3226b158e67c ("net: avoid 32 x truesize under-estimation for tiny skbs") because GRO was using 2 frags per MSS, meaning we were not packing MSS with 100% efficiency. Fix is to pull only the ethernet header in page_to_skb() Then, we change virtio_net_hdr_to_skb() to pull the missing headers, instead of assuming they were already pulled by callers. This fixes the performance regression, but could also allow virtio_net to accept packets with more than 128bytes of headers. Many thanks to Xuan Zhuo for his report, and his tests/help. Fixes: 3226b158e67c ("net: avoid 32 x truesize under-estimation for tiny skbs") Reported-by: Xuan Zhuo Link: https://www.spinics.net/lists/netdev/msg731397.html Co-Developed-by: Xuan Zhuo Signed-off-by: Xuan Zhuo Signed-off-by: Eric Dumazet Cc: "Michael S. Tsirkin" Cc: Jason Wang Cc: virtualization@lists.linux-foundation.org --- drivers/net/virtio_net.c | 10 +++++++--- include/linux/virtio_net.h | 14 +++++++++----- 2 files changed, 16 insertions(+), 8 deletions(-) diff --git a/drivers/net/virtio_net.c b/drivers/net/virtio_net.c index 82e520d2cb1229a0c7b9fd0def3e4a7135536478..0824e6999e49957f7aaf7c990f6259792d42f32b 100644 --- a/drivers/net/virtio_net.c +++ b/drivers/net/virtio_net.c @@ -406,9 +406,13 @@ static struct sk_buff *page_to_skb(struct virtnet_info *vi, offset += hdr_padded_len; p += hdr_padded_len; - copy = len; - if (copy > skb_tailroom(skb)) - copy = skb_tailroom(skb); + /* Copy all frame if it fits skb->head, otherwise + * we let virtio_net_hdr_to_skb() and GRO pull headers as needed. + */ + if (len <= skb_tailroom(skb)) + copy = len; + else + copy = ETH_HLEN + metasize; skb_put_data(skb, p, copy); if (metasize) { diff --git a/include/linux/virtio_net.h b/include/linux/virtio_net.h index 98775d7fa69632e2c2da30b581a666f7fbb94b64..b465f8f3e554f27ced45c35f54f113cf6dce1f07 100644 --- a/include/linux/virtio_net.h +++ b/include/linux/virtio_net.h @@ -65,14 +65,18 @@ static inline int virtio_net_hdr_to_skb(struct sk_buff *skb, skb_reset_mac_header(skb); if (hdr->flags & VIRTIO_NET_HDR_F_NEEDS_CSUM) { - u16 start = __virtio16_to_cpu(little_endian, hdr->csum_start); - u16 off = __virtio16_to_cpu(little_endian, hdr->csum_offset); + u32 start = __virtio16_to_cpu(little_endian, hdr->csum_start); + u32 off = __virtio16_to_cpu(little_endian, hdr->csum_offset); + u32 needed = start + max_t(u32, thlen, off + sizeof(__sum16)); + + if (!pskb_may_pull(skb, needed)) + return -EINVAL; if (!skb_partial_csum_set(skb, start, off)) return -EINVAL; p_off = skb_transport_offset(skb) + thlen; - if (p_off > skb_headlen(skb)) + if (!pskb_may_pull(skb, p_off)) return -EINVAL; } else { /* gso packets without NEEDS_CSUM do not set transport_offset. @@ -102,14 +106,14 @@ static inline int virtio_net_hdr_to_skb(struct sk_buff *skb, } p_off = keys.control.thoff + thlen; - if (p_off > skb_headlen(skb) || + if (!pskb_may_pull(skb, p_off) || keys.basic.ip_proto != ip_proto) return -EINVAL; skb_set_transport_header(skb, keys.control.thoff); } else if (gso_type) { p_off = thlen; - if (p_off > skb_headlen(skb)) + if (!pskb_may_pull(skb, p_off)) return -EINVAL; } } -- 2.31.0.208.g409f899ff0-goog