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 0E5FDC46467 for ; Tue, 27 Dec 2022 09:10:54 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S229791AbiL0JKv (ORCPT ); Tue, 27 Dec 2022 04:10:51 -0500 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:46540 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S229792AbiL0JKi (ORCPT ); Tue, 27 Dec 2022 04:10:38 -0500 Received: from out30-57.freemail.mail.aliyun.com (out30-57.freemail.mail.aliyun.com [115.124.30.57]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id DB4897679; Tue, 27 Dec 2022 01:10:36 -0800 (PST) X-Alimail-AntiSpam: AC=PASS;BC=-1|-1;BR=01201311R741e4;CH=green;DM=||false|;DS=||;FP=0|-1|-1|-1|0|-1|-1|-1;HT=ay29a033018045170;MF=hengqi@linux.alibaba.com;NM=1;PH=DS;RN=12;SR=0;TI=SMTPD_---0VYCy1cT_1672132233; Received: from 30.120.189.46(mailfrom:hengqi@linux.alibaba.com fp:SMTPD_---0VYCy1cT_1672132233) by smtp.aliyun-inc.com; Tue, 27 Dec 2022 17:10:34 +0800 Message-ID: <8aa5b8fb-d766-ac84-dfc1-4f9947e86e27@linux.alibaba.com> Date: Tue, 27 Dec 2022 17:10:31 +0800 MIME-Version: 1.0 User-Agent: Mozilla/5.0 (Macintosh; Intel Mac OS X 10.15; rv:108.0) Gecko/20100101 Thunderbird/108.0 Subject: Re: [PATCH v2 4/9] virtio_net: build xdp_buff with multi buffers To: Jason Wang , netdev@vger.kernel.org, bpf@vger.kernel.org Cc: "Michael S . Tsirkin" , Paolo Abeni , Jakub Kicinski , John Fastabend , "David S . Miller" , Daniel Borkmann , Alexei Starovoitov , Eric Dumazet , Xuan Zhuo References: <20221220141449.115918-1-hengqi@linux.alibaba.com> <20221220141449.115918-5-hengqi@linux.alibaba.com> From: Heng Qi In-Reply-To: Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 8bit Precedence: bulk List-ID: X-Mailing-List: netdev@vger.kernel.org 在 2022/12/27 下午2:46, Jason Wang 写道: > > 在 2022/12/20 22:14, Heng Qi 写道: >> Support xdp for multi buffer packets in mergeable mode. >> >> Putting the first buffer as the linear part for xdp_buff, >> and the rest of the buffers as non-linear fragments to struct >> skb_shared_info in the tailroom belonging to xdp_buff. >> >> Signed-off-by: Heng Qi >> Reviewed-by: Xuan Zhuo >> --- >>   drivers/net/virtio_net.c | 78 ++++++++++++++++++++++++++++++++++++++++ >>   1 file changed, 78 insertions(+) >> >> diff --git a/drivers/net/virtio_net.c b/drivers/net/virtio_net.c >> index 08f209d7b0bf..8fc3b1841d92 100644 >> --- a/drivers/net/virtio_net.c >> +++ b/drivers/net/virtio_net.c >> @@ -931,6 +931,84 @@ static struct sk_buff *receive_big(struct >> net_device *dev, >>       return NULL; >>   } >>   +/* TODO: build xdp in big mode */ >> +static int virtnet_build_xdp_buff_mrg(struct net_device *dev, >> +                      struct virtnet_info *vi, >> +                      struct receive_queue *rq, >> +                      struct xdp_buff *xdp, >> +                      void *buf, >> +                      unsigned int len, >> +                      unsigned int frame_sz, >> +                      u16 *num_buf, >> +                      unsigned int *xdp_frags_truesize, >> +                      struct virtnet_rq_stats *stats) >> +{ >> +    unsigned int tailroom = SKB_DATA_ALIGN(sizeof(struct >> skb_shared_info)); >> +    struct virtio_net_hdr_mrg_rxbuf *hdr = buf; >> +    unsigned int truesize, headroom; >> +    struct skb_shared_info *shinfo; >> +    unsigned int xdp_frags_truesz = 0; >> +    unsigned int cur_frag_size; >> +    struct page *page; >> +    skb_frag_t *frag; >> +    int offset; >> +    void *ctx; >> + >> +    xdp_init_buff(xdp, frame_sz, &rq->xdp_rxq); >> +    xdp_prepare_buff(xdp, buf - VIRTIO_XDP_HEADROOM, >> +             VIRTIO_XDP_HEADROOM + vi->hdr_len, len - vi->hdr_len, >> true); >> + >> +    if (*num_buf > 1) { >> +        shinfo = xdp_get_shared_info_from_buff(xdp); >> +        shinfo->nr_frags = 0; >> +        shinfo->xdp_frags_size = 0; >> +    } >> + >> +    if ((*num_buf - 1) > MAX_SKB_FRAGS) >> +        return -EINVAL; >> + >> +    while ((--*num_buf) >= 1) { >> +        buf = virtqueue_get_buf_ctx(rq->vq, &len, &ctx); >> +        if (unlikely(!buf)) { >> +            pr_debug("%s: rx error: %d buffers out of %d missing\n", >> +                 dev->name, *num_buf, >> +                 virtio16_to_cpu(vi->vdev, hdr->num_buffers)); >> +            dev->stats.rx_length_errors++; >> +            return -EINVAL; >> +        } >> + >> +        if (!xdp_buff_has_frags(xdp)) >> +            xdp_buff_set_frags_flag(xdp); > > > Any reason to put this inside the loop? I'll move it outside the loop in the next version. > > >> + >> +        stats->bytes += len; >> +        page = virt_to_head_page(buf); >> +        offset = buf - page_address(page); >> +        truesize = mergeable_ctx_to_truesize(ctx); >> +        headroom = mergeable_ctx_to_headroom(ctx); >> + >> +        cur_frag_size = truesize + (headroom ? (headroom + tailroom) >> : 0); >> +        xdp_frags_truesz += cur_frag_size; > > > Not related to this patch, but it would easily confuse the future > readers that the we need another math for truesize. I think at least > we need some comments for this or Yes it might, I'll add more comments on this. > > I guess the root cause is in get_mergeable_buf_len: > > static unsigned int get_mergeable_buf_len(struct receive_queue *rq, >                                       struct ewma_pkt_len *avg_pkt_len, >                                           unsigned int room) > { >         struct virtnet_info *vi = rq->vq->vdev->priv; >         const size_t hdr_len = vi->hdr_len; >         unsigned int len; > >         if (room) >         return PAGE_SIZE - room; > > And we do > >     len = get_mergeable_buf_len(rq, &rq->mrg_avg_pkt_len, room); > >     ... > >     ctx = mergeable_len_to_ctx(len, headroom); > > > I wonder if it's better to pack the real truesize (PAGE_SIZE) here. > This may ease a lot of things. I don't know the historical reason for not packing, but I guess this is for the convenience of comparing the actual length len given by the device with truesize. Therefore, I think it would be better to keep the above practice for now? Perhaps, I can add more explanation to the above code to help future readers try not to get confused. Thanks. > > Thanks > > >> +        if (unlikely(len > truesize || cur_frag_size > PAGE_SIZE)) { >> +            pr_debug("%s: rx error: len %u exceeds truesize %lu\n", >> +                 dev->name, len, (unsigned long)ctx); >> +            dev->stats.rx_length_errors++; >> +            return -EINVAL; >> +        } >> + >> +        frag = &shinfo->frags[shinfo->nr_frags++]; >> +        __skb_frag_set_page(frag, page); >> +        skb_frag_off_set(frag, offset); >> +        skb_frag_size_set(frag, len); >> +        if (page_is_pfmemalloc(page)) >> +            xdp_buff_set_frag_pfmemalloc(xdp); >> + >> +        shinfo->xdp_frags_size += len; >> +    } >> + >> +    *xdp_frags_truesize = xdp_frags_truesz; >> +    return 0; >> +} >> + >>   static struct sk_buff *receive_mergeable(struct net_device *dev, >>                        struct virtnet_info *vi, >>                        struct receive_queue *rq,