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 Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id 54AA3C46467 for ; Wed, 28 Dec 2022 08:23:11 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S229997AbiL1IXK (ORCPT ); Wed, 28 Dec 2022 03:23:10 -0500 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:41104 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S229665AbiL1IXI (ORCPT ); Wed, 28 Dec 2022 03:23:08 -0500 Received: from out30-44.freemail.mail.aliyun.com (out30-44.freemail.mail.aliyun.com [115.124.30.44]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id CDB40E24; Wed, 28 Dec 2022 00:23:06 -0800 (PST) X-Alimail-AntiSpam: AC=PASS;BC=-1|-1;BR=01201311R821e4;CH=green;DM=||false|;DS=||;FP=0|-1|-1|-1|0|-1|-1|-1;HT=ay29a033018045168;MF=hengqi@linux.alibaba.com;NM=1;PH=DS;RN=12;SR=0;TI=SMTPD_---0VYGgrWv_1672215781; Received: from localhost(mailfrom:hengqi@linux.alibaba.com fp:SMTPD_---0VYGgrWv_1672215781) by smtp.aliyun-inc.com; Wed, 28 Dec 2022 16:23:02 +0800 Date: Wed, 28 Dec 2022 16:23:01 +0800 From: Heng Qi To: Jason Wang Cc: netdev@vger.kernel.org, bpf@vger.kernel.org, "Michael S . Tsirkin" , Paolo Abeni , Jakub Kicinski , John Fastabend , "David S . Miller" , Daniel Borkmann , Alexei Starovoitov , Eric Dumazet , Xuan Zhuo Subject: Re: [PATCH v2 5/9] virtio_net: construct multi-buffer xdp in mergeable Message-ID: <20221228082301.GA18313@h68b04307.sqa.eu95> References: <20221220141449.115918-1-hengqi@linux.alibaba.com> <20221220141449.115918-6-hengqi@linux.alibaba.com> <5a03364e-c09e-63ff-7e73-1efec1ed8ca8@redhat.com> <83dc59b1-99f6-58fe-56b5-de5158bcc3cd@linux.alibaba.com> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: User-Agent: Mutt/1.5.21 (2010-09-15) Precedence: bulk List-ID: X-Mailing-List: netdev@vger.kernel.org On Wed, Dec 28, 2022 at 02:24:22PM +0800, Jason Wang wrote: > > 在 2022/12/27 17:31, Heng Qi 写道: > > > > > >在 2022/12/27 下午3:01, Jason Wang 写道: > >> > >>在 2022/12/20 22:14, Heng Qi 写道: > >>>Build multi-buffer xdp using virtnet_build_xdp_buff_mrg(). > >>> > >>>For the prefilled buffer before xdp is set, we will probably use > >>>vq reset in the future. At the same time, virtio net currently > >>>uses comp pages, and bpf_xdp_frags_increase_tail() needs to calculate > >>>the tailroom of the last frag, which will involve the offset of the > >>>corresponding page and cause a negative value, so we disable tail > >>>increase by not setting xdp_rxq->frag_size. > >>> > >>>Signed-off-by: Heng Qi > >>>Reviewed-by: Xuan Zhuo > >>>--- > >>>  drivers/net/virtio_net.c | 60 > >>>+++++++++++++++++++++++++++++----------- > >>>  1 file changed, 44 insertions(+), 16 deletions(-) > >>> > >>>diff --git a/drivers/net/virtio_net.c b/drivers/net/virtio_net.c > >>>index 8fc3b1841d92..40bc58fa57f5 100644 > >>>--- a/drivers/net/virtio_net.c > >>>+++ b/drivers/net/virtio_net.c > >>>@@ -1018,6 +1018,7 @@ static struct sk_buff > >>>*receive_mergeable(struct net_device *dev, > >>>                       unsigned int *xdp_xmit, > >>>                       struct virtnet_rq_stats *stats) > >>>  { > >>>+    unsigned int tailroom = SKB_DATA_ALIGN(sizeof(struct > >>>skb_shared_info)); > >>>      struct virtio_net_hdr_mrg_rxbuf *hdr = buf; > >>>      u16 num_buf = virtio16_to_cpu(vi->vdev, hdr->num_buffers); > >>>      struct page *page = virt_to_head_page(buf); > >>>@@ -1048,11 +1049,14 @@ static struct sk_buff > >>>*receive_mergeable(struct net_device *dev, > >>>      rcu_read_lock(); > >>>      xdp_prog = rcu_dereference(rq->xdp_prog); > >>>      if (xdp_prog) { > >>>+        unsigned int xdp_frags_truesz = 0; > >>>+        struct skb_shared_info *shinfo; > >>>          struct xdp_frame *xdpf; > >>>          struct page *xdp_page; > >>>          struct xdp_buff xdp; > >>>          void *data; > >>>          u32 act; > >>>+        int i; > >>>            /* Transient failure which in theory could occur if > >>>           * in-flight packets from before XDP was enabled reach > >>>@@ -1061,19 +1065,23 @@ static struct sk_buff > >>>*receive_mergeable(struct net_device *dev, > >>>          if (unlikely(hdr->hdr.gso_type)) > >>>              goto err_xdp; > >>>  -        /* Buffers with headroom use PAGE_SIZE as alloc size, > >>>-         * see add_recvbuf_mergeable() + get_mergeable_buf_len() > >>>+        /* Now XDP core assumes frag size is PAGE_SIZE, but buffers > >>>+         * with headroom may add hole in truesize, which > >>>+         * make their length exceed PAGE_SIZE. So we disabled the > >>>+         * hole mechanism for xdp. See add_recvbuf_mergeable(). > >>>           */ > >>>          frame_sz = headroom ? PAGE_SIZE : truesize; > >>>  -        /* This happens when rx buffer size is underestimated > >>>-         * or headroom is not enough because of the buffer > >>>-         * was refilled before XDP is set. This should only > >>>-         * happen for the first several packets, so we don't > >>>-         * care much about its performance. > >>>+        /* This happens when headroom is not enough because > >>>+         * of the buffer was prefilled before XDP is set. > >>>+         * This should only happen for the first several packets. > >>>+         * In fact, vq reset can be used here to help us clean up > >>>+         * the prefilled buffers, but many existing devices do not > >>>+         * support it, and we don't want to bother users who are > >>>+         * using xdp normally. > >>>           */ > >>>-        if (unlikely(num_buf > 1 || > >>>-                 headroom < virtnet_get_headroom(vi))) { > >>>+        if (!xdp_prog->aux->xdp_has_frags && > >>>+            (num_buf > 1 || headroom < virtnet_get_headroom(vi))) { > >>>              /* linearize data for XDP */ > >>>              xdp_page = xdp_linearize_page(rq, &num_buf, > >>>                                page, offset, > >>>@@ -1084,17 +1092,26 @@ static struct sk_buff > >>>*receive_mergeable(struct net_device *dev, > >>>              if (!xdp_page) > >>>                  goto err_xdp; > >>>              offset = VIRTIO_XDP_HEADROOM; > >>>+        } else if (unlikely(headroom < virtnet_get_headroom(vi))) { > >> > >> > >>I believe we need to check xdp_prog->aux->xdp_has_frags at least > >>since this may not work if it needs more than one frags? > > > >Sorry Jason, I didn't understand you, I'll try to answer. For > >multi-buffer xdp programs, if the first buffer is a pre-filled > >buffer (no headroom), > >we need to copy it out and use the subsequent buffers of this > >packet as its frags (this is done in > >virtnet_build_xdp_buff_mrg()), therefore, > >it seems that there is no need to check > >'xdp_prog->aux->xdp_has_frags' to mark multi-buffer xdp (of course > >I can add it), > > > >+ } else if (unlikely(headroom < virtnet_get_headroom(vi))) { > > > >Because the linearization of single-buffer xdp has all been done > >before, the subsequent situation can only be applied to > >multi-buffer xdp: > >+ if (!xdp_prog->aux->xdp_has_frags && > >+ (num_buf > 1 || headroom < virtnet_get_headroom(vi))) { > > > I basically meant what happens if > > !xdp_prog->aux->xdp_has_frags && num_buf > 2 && headroom < > virtnet_get_headroom(vi) > > In this case the current code seems to leave the second buffer in > the frags. This is the case of the buffer size underestimation that > is mentioned in the comment before (I'd like to keep that). If I'm not wrong, this case is still directly into the first 'if' loop. - if (unlikely(num_buf > 1 || - headroom < virtnet_get_headroom(vi))) { + if (!xdp_prog->aux->xdp_has_frags && + (num_buf > 1 || headroom < virtnet_get_headroom(vi))) { Thanks. > > (And that's why I'm asking to use linearizge_page()) > > Thanks > > > > > >> > >>Btw, I don't see a reason why we can't reuse > >>xdp_linearize_page(), (we probably don't need error is the > >>buffer exceeds PAGE_SIZE). > > > >For multi-buffer xdp, we only need to copy out the pre-filled > >first buffer, and use the remaining buffers of this packet as > >frags in virtnet_build_xdp_buff_mrg(). > > > >Thanks. > > > >> > >>Other looks good. > >> > >>Thanks > >> > >> > >>>+            if ((VIRTIO_XDP_HEADROOM + len + tailroom) > PAGE_SIZE) > >>>+                goto err_xdp; > >>>+ > >>>+            xdp_page = alloc_page(GFP_ATOMIC); > >>>+            if (!xdp_page) > >>>+                goto err_xdp; > >>>+ > >>>+            memcpy(page_address(xdp_page) + VIRTIO_XDP_HEADROOM, > >>>+                   page_address(page) + offset, len); > >>>+            frame_sz = PAGE_SIZE; > >>>+            offset = VIRTIO_XDP_HEADROOM; > >>>          } else { > >>>              xdp_page = page; > >>>          } > >>>- > >>>-        /* Allow consuming headroom but reserve enough space to push > >>>-         * the descriptor on if we get an XDP_TX return code. > >>>-         */ > >>>          data = page_address(xdp_page) + offset; > >>>-        xdp_init_buff(&xdp, frame_sz - vi->hdr_len, &rq->xdp_rxq); > >>>-        xdp_prepare_buff(&xdp, data - VIRTIO_XDP_HEADROOM + > >>>vi->hdr_len, > >>>-                 VIRTIO_XDP_HEADROOM, len - vi->hdr_len, true); > >>>+        err = virtnet_build_xdp_buff_mrg(dev, vi, rq, &xdp, > >>>data, len, frame_sz, > >>>+                         &num_buf, &xdp_frags_truesz, stats); > >>>+        if (unlikely(err)) > >>>+            goto err_xdp_frags; > >>>            act = bpf_prog_run_xdp(xdp_prog, &xdp); > >>>          stats->xdp_packets++; > >>>@@ -1190,6 +1207,17 @@ static struct sk_buff > >>>*receive_mergeable(struct net_device *dev, > >>>                  __free_pages(xdp_page, 0); > >>>              goto err_xdp; > >>>          } > >>>+err_xdp_frags: > >>>+        shinfo = xdp_get_shared_info_from_buff(&xdp); > >>>+ > >>>+        if (unlikely(xdp_page != page)) > >>>+            __free_pages(xdp_page, 0); > >>>+ > >>>+        for (i = 0; i < shinfo->nr_frags; i++) { > >>>+            xdp_page = skb_frag_page(&shinfo->frags[i]); > >>>+            put_page(xdp_page); > >>>+        } > >>>+        goto err_xdp; > >>>      } > >>>      rcu_read_unlock(); > >