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=-12.7 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,URIBL_BLOCKED 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 B66A3C433E0 for ; Fri, 22 Jan 2021 19:41:41 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 81FE923A6A for ; Fri, 22 Jan 2021 19:41:41 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1730366AbhAVTkC (ORCPT ); Fri, 22 Jan 2021 14:40:02 -0500 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:49206 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1728425AbhAVSh7 (ORCPT ); Fri, 22 Jan 2021 13:37:59 -0500 Received: from mail-pj1-x1036.google.com (mail-pj1-x1036.google.com [IPv6:2607:f8b0:4864:20::1036]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id CA112C061788; Fri, 22 Jan 2021 10:37:18 -0800 (PST) Received: by mail-pj1-x1036.google.com with SMTP id u4so4448365pjn.4; Fri, 22 Jan 2021 10:37:18 -0800 (PST) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmail.com; s=20161025; h=mime-version:references:in-reply-to:from:date:message-id:subject:to :cc; bh=qaA8gn8W+Qu4RF9KetEmDBu/lptRV9ahKpJnZpI7ZCo=; b=Q9HhAWjka/fgAdf6tIezBrvuW0cqacMGrv5pjCFzngBW44GQxtCcNZSPne3ymkCfhg YYBo+8Ei8TAYYjJ5Eu0diMLL+MuMDVtQA+Lb6IpKqVcDzM+zoAWjORzSs53tAddbxY2v m6GqvrK8kuPKSk6uttoSnbJ7XUr5BYvXs+mDNZWqR0ov5GMYmL9yCbH8WNg43XU8/DkA j9RdPlvHhj/EhnQqqTlwDoKourDCNC87oFvQblXxjzZ5zZsHQ5Il3ec9mwQAtteMk3pq Uuxe9dHerS5Ii5o55wbA5hmc1BRFS7V4SqI10Vh0b5x+3zqzhLr5459nwZct7Yl98Ynt 9wgQ== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20161025; h=x-gm-message-state:mime-version:references:in-reply-to:from:date :message-id:subject:to:cc; bh=qaA8gn8W+Qu4RF9KetEmDBu/lptRV9ahKpJnZpI7ZCo=; b=LEOzMtiS1DypVUxJS0fDijXKW6aBlyZmjn9rmMjhFAQsy61pkPFR2IXK2lMbCT16Ue 8KwOZ8ZwvgN7XiP+bSXKtlY8dqYb+5bMH8Uxm+9KL8iWEzSzyGBh10r1EwKahQMjB9Jr ArI1VrsAQJGg7fk+9oDyD17v73Gg673CpeIsNWQ6egC6cbZuVg2wLO3bJ31QhHpDI27T ehYyeRrwsAvIkv5/xw1Wtjz3UnqxEns4xQnAzPY+E+nFECB0yHvjz5GxXTZ6dzssSRqZ Hw5yLWjra3rW5d9IOVi8lGLAK4nPUPPQknMrmbbfiyGS+PTTBvtff1iZEs3jEv6teWTj S9Zw== X-Gm-Message-State: AOAM533P6V/PvQt3qPtPn+RbRKOdfatEkEkEhj3YXjIf0bke79V/2/iy ud2tBwxYvoAQD2PQPDoP0NJax0DIrSKJVGs1NwrGeMrMgyG3UQ== X-Google-Smtp-Source: ABdhPJzBM0YzSfYP6oM7kRIRx6dclFXfHRC0Ic0kFqaNBSS+HPxNtv8ookM9vpCOGsNT+AdZ+FmAMIpQ8Gfu0nU/hJY= X-Received: by 2002:a17:902:7c04:b029:dc:99f2:eea4 with SMTP id x4-20020a1709027c04b02900dc99f2eea4mr5931479pll.43.1611340638255; Fri, 22 Jan 2021 10:37:18 -0800 (PST) MIME-Version: 1.0 References: <1611329955.4913929-2-xuanzhuo@linux.alibaba.com> <20210122172534.9896-1-alobakin@pm.me> In-Reply-To: <20210122172534.9896-1-alobakin@pm.me> From: Magnus Karlsson Date: Fri, 22 Jan 2021 19:37:06 +0100 Message-ID: Subject: Re: [PATCH bpf-next v3 3/3] xsk: build skb by page To: Alexander Lobakin Cc: Xuan Zhuo , Eric Dumazet , "Michael S . Tsirkin" , Jason Wang , "David S . Miller" , Jakub Kicinski , Bjorn Topel , Magnus Karlsson , Jonathan Lemon , Alexei Starovoitov , Daniel Borkmann , Jesper Dangaard Brouer , John Fastabend , Andrii Nakryiko , Martin KaFai Lau , Song Liu , Yonghong Song , KP Singh , virtualization@lists.linux-foundation.org, bpf , Network Development , open list Content-Type: text/plain; charset="UTF-8" Precedence: bulk List-ID: X-Mailing-List: bpf@vger.kernel.org On Fri, Jan 22, 2021 at 6:26 PM Alexander Lobakin wrote: > > From: Xuan Zhuo > Date: Fri, 22 Jan 2021 23:39:15 +0800 > > > On Fri, 22 Jan 2021 13:55:14 +0100, Magnus Karlsson wrote: > > > On Fri, Jan 22, 2021 at 1:39 PM Alexander Lobakin wrote: > > > > > > > > From: Magnus Karlsson > > > > Date: Fri, 22 Jan 2021 13:18:47 +0100 > > > > > > > > > On Fri, Jan 22, 2021 at 12:57 PM Alexander Lobakin wrote: > > > > > > > > > > > > From: Alexander Lobakin > > > > > > Date: Fri, 22 Jan 2021 11:47:45 +0000 > > > > > > > > > > > > > From: Eric Dumazet > > > > > > > Date: Thu, 21 Jan 2021 16:41:33 +0100 > > > > > > > > > > > > > > > On 1/21/21 2:47 PM, Xuan Zhuo wrote: > > > > > > > > > This patch is used to construct skb based on page to save memory copy > > > > > > > > > overhead. > > > > > > > > > > > > > > > > > > This function is implemented based on IFF_TX_SKB_NO_LINEAR. Only the > > > > > > > > > network card priv_flags supports IFF_TX_SKB_NO_LINEAR will use page to > > > > > > > > > directly construct skb. If this feature is not supported, it is still > > > > > > > > > necessary to copy data to construct skb. > > > > > > > > > > > > > > > > > > ---------------- Performance Testing ------------ > > > > > > > > > > > > > > > > > > The test environment is Aliyun ECS server. > > > > > > > > > Test cmd: > > > > > > > > > ``` > > > > > > > > > xdpsock -i eth0 -t -S -s > > > > > > > > > ``` > > > > > > > > > > > > > > > > > > Test result data: > > > > > > > > > > > > > > > > > > size 64 512 1024 1500 > > > > > > > > > copy 1916747 1775988 1600203 1440054 > > > > > > > > > page 1974058 1953655 1945463 1904478 > > > > > > > > > percent 3.0% 10.0% 21.58% 32.3% > > > > > > > > > > > > > > > > > > Signed-off-by: Xuan Zhuo > > > > > > > > > Reviewed-by: Dust Li > > > > > > > > > --- > > > > > > > > > net/xdp/xsk.c | 104 ++++++++++++++++++++++++++++++++++++++++++++++++---------- > > > > > > > > > 1 file changed, 86 insertions(+), 18 deletions(-) > > > > > > > > > > > > > > > > > > diff --git a/net/xdp/xsk.c b/net/xdp/xsk.c > > > > > > > > > index 4a83117..38af7f1 100644 > > > > > > > > > --- a/net/xdp/xsk.c > > > > > > > > > +++ b/net/xdp/xsk.c > > > > > > > > > @@ -430,6 +430,87 @@ static void xsk_destruct_skb(struct sk_buff *skb) > > > > > > > > > sock_wfree(skb); > > > > > > > > > } > > > > > > > > > > > > > > > > > > +static struct sk_buff *xsk_build_skb_zerocopy(struct xdp_sock *xs, > > > > > > > > > + struct xdp_desc *desc) > > > > > > > > > +{ > > > > > > > > > + u32 len, offset, copy, copied; > > > > > > > > > + struct sk_buff *skb; > > > > > > > > > + struct page *page; > > > > > > > > > + void *buffer; > > > > > > > > > + int err, i; > > > > > > > > > + u64 addr; > > > > > > > > > + > > > > > > > > > + skb = sock_alloc_send_skb(&xs->sk, 0, 1, &err); > > > > > > > > > + if (unlikely(!skb)) > > > > > > > > > + return ERR_PTR(err); > > > > > > > > > + > > > > > > > > > + addr = desc->addr; > > > > > > > > > + len = desc->len; > > > > > > > > > + > > > > > > > > > + buffer = xsk_buff_raw_get_data(xs->pool, addr); > > > > > > > > > + offset = offset_in_page(buffer); > > > > > > > > > + addr = buffer - xs->pool->addrs; > > > > > > > > > + > > > > > > > > > + for (copied = 0, i = 0; copied < len; i++) { > > > > > > > > > + page = xs->pool->umem->pgs[addr >> PAGE_SHIFT]; > > > > > > > > > + > > > > > > > > > + get_page(page); > > > > > > > > > + > > > > > > > > > + copy = min_t(u32, PAGE_SIZE - offset, len - copied); > > > > > > > > > + > > > > > > > > > + skb_fill_page_desc(skb, i, page, offset, copy); > > > > > > > > > + > > > > > > > > > + copied += copy; > > > > > > > > > + addr += copy; > > > > > > > > > + offset = 0; > > > > > > > > > + } > > > > > > > > > + > > > > > > > > > + skb->len += len; > > > > > > > > > + skb->data_len += len; > > > > > > > > > > > > > > > > > + skb->truesize += len; > > > > > > > > > > > > > > > > This is not the truesize, unfortunately. > > > > > > > > > > > > > > > > We need to account for the number of pages, not number of bytes. > > > > > > > > > > > > > > The easiest solution is: > > > > > > > > > > > > > > skb->truesize += PAGE_SIZE * i; > > > > > > > > > > > > > > i would be equal to skb_shinfo(skb)->nr_frags after exiting the loop. > > > > > > > > > > > > Oops, pls ignore this. I forgot that XSK buffers are not > > > > > > "one per page". > > > > > > We need to count the number of pages manually and then do > > > > > > > > > > > > skb->truesize += PAGE_SIZE * npages; > > > > > > > > > > > > Right. > > > > > > > > > > There are two possible packet buffer (chunks) sizes in a umem, 2K and > > > > > 4K on a system with a PAGE_SIZE of 4K. If I remember correctly, and > > > > > please correct me if wrong, truesize is used for memory accounting. > > > > > But in this code, no kernel memory has been allocated (apart from the > > > > > skb). The page is just a part of the umem that has been already > > > > > allocated beforehand and by user-space in this case. So what should > > > > > truesize be in this case? Do we add 0, chunk_size * i, or the > > > > > complicated case of counting exactly how many 4K pages that are used > > > > > when the chunk_size is 2K, as two chunks could occupy the same page, > > > > > or just the upper bound of PAGE_SIZE * i that is likely a good > > > > > approximation in most cases? Just note that there might be other uses > > > > > of truesize that I am unaware of that could impact this choice. > > > > > > > > Truesize is "what amount of memory does this skb occupy with all its > > > > fragments, linear space and struct sk_buff itself". The closest it > > > > will be to the actual value, the better. > > > > In this case, I think adding of chunk_size * i would be enough. > > > > > > Sounds like a good approximation to me. > > > > > > > (PAGE_SIZE * i can be overwhelming when chunk_size is 2K, especially > > > > for setups with PAGE_SIZE > SZ_4K) > > > > > > You are right. That would be quite horrible on a system with a page size of 64K. > > > > Thank you everyone, I learned it. > > > > I also think it is appropriate to add a chunk size here, and there is actually > > only one chunk here, so it's very simple > > > > skb->truesize += xs->pool->chunk_size; > > umem chunks can't cross page boundaries. So if you're sure that > there could be only one chunk, you don't need the loop at all, > if I'm not missing anything. In the default mode, this is true. But in the unaligned_chunk mode that can be set on the umem, the chunk may cross one page boundary, so we need the loop and the chunk_size * i in the assignment of truesize. So "i" can be 1 or 2, but nothing else. > > In addition, I actually borrowed from the tcp code: > > > > tcp_build_frag: > > -------------- > > > > if (can_coalesce) { > > skb_frag_size_add(&skb_shinfo(skb)->frags[i - 1], copy); > > } else { > > get_page(page); > > skb_fill_page_desc(skb, i, page, offset, copy); > > } > > > > if (!(flags & MSG_NO_SHARED_FRAGS)) > > skb_shinfo(skb)->flags |= SKBFL_SHARED_FRAG; > > > > skb->len += copy; > > skb->data_len += copy; > > skb->truesize += copy; > > > > So, here is one bug? > > skb_frag_t is an alias to struct bvec. It doesn't contain info about > real memory consumption, so there's no other option buf just to add > "copy" to truesize. > XSK is different in this term, as it operates with chunks of a known > size. > > > Thanks. > > > > > > > > > > > > > > + > > > > > > > > > + refcount_add(len, &xs->sk.sk_wmem_alloc); > > > > > > > > > + > > > > > > > > > + return skb; > > > > > > > > > +} > > > > > > > > > + > > > > > > > > > > > > > > Al > > > > > > > > > > > > Thanks, > > > > > > Al > > > > > > > > Al >