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=-15.8 required=3.0 tests=BAYES_00,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_CR_TRAILER, INCLUDES_PATCH,MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS,URIBL_BLOCKED autolearn=unavailable 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 2195DC433E9 for ; Fri, 22 Jan 2021 22:59:52 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id E0DF923ACA for ; Fri, 22 Jan 2021 22:59:51 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1730862AbhAVTkk (ORCPT ); Fri, 22 Jan 2021 14:40:40 -0500 Received: from mail2.protonmail.ch ([185.70.40.22]:63013 "EHLO mail2.protonmail.ch" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1729752AbhAVSqg (ORCPT ); Fri, 22 Jan 2021 13:46:36 -0500 Date: Fri, 22 Jan 2021 18:45:33 +0000 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=pm.me; s=protonmail; t=1611341138; bh=2ILzHi/ReYeZyxyrJVxJwSXtgiG9Sy5HC6N/+GXYepg=; h=Date:To:From:Cc:Reply-To:Subject:In-Reply-To:References:From; b=YPsITljI0xVWT7arGTO6Fep3NgpuTX8DMLiLb6ohxQO8xHqcLBtYay69XrBkuOwjr 49z+Ff4ysFCxhp9Od96KjzxzP9ZVvQQMb1SX4iuT2Rj9gCzWNEBSiBQsymrVi1ntOB c0UovLfOooz55rkDjzOh5MQXeUOXE0huVIjfD3LhZdwd0o61dNGDGS+M9neiGJ/woE AgI28xjGVmh96KupPcjtF/soRBSwad/UayBSdXz0Ta0mXEyacpI+FlZxIRvNWki3eF MOgGkr/d6mHNNt93Vw1tMgzbWXBRbSRopf6IiWfA5M/u7bGHbYTIyDyzH+G2KO0wj+ oWy/372pR8YaQ== To: Magnus Karlsson From: Alexander Lobakin Cc: Alexander Lobakin , 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 Reply-To: Alexander Lobakin Subject: Re: [PATCH bpf-next v3 3/3] xsk: build skb by page Message-ID: <20210122184457.37812-1-alobakin@pm.me> In-Reply-To: References: <1611329955.4913929-2-xuanzhuo@linux.alibaba.com> <20210122172534.9896-1-alobakin@pm.me> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: quoted-printable Precedence: bulk List-ID: X-Mailing-List: bpf@vger.kernel.org From: Magnus Karlsson Date: Fri, 22 Jan 2021 19:37:06 +0100 > 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 sa= ve memory copy > > > > > > > > > > overhead. > > > > > > > > > > > > > > > > > > > > This function is implemented based on IFF_TX_SKB_NO_LIN= EAR. Only the > > > > > > > > > > network card priv_flags supports IFF_TX_SKB_NO_LINEAR w= ill use page to > > > > > > > > > > directly construct skb. If this feature is not supporte= d, 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(struc= t sk_buff *skb) > > > > > > > > > > sock_wfree(skb); > > > > > > > > > > } > > > > > > > > > > > > > > > > > > > > +static struct sk_buff *xsk_build_skb_zerocopy(struct x= dp_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 =3D sock_alloc_send_skb(&xs->sk, 0, 1, &err); > > > > > > > > > > + if (unlikely(!skb)) > > > > > > > > > > + return ERR_PTR(err); > > > > > > > > > > + > > > > > > > > > > + addr =3D desc->addr; > > > > > > > > > > + len =3D desc->len; > > > > > > > > > > + > > > > > > > > > > + buffer =3D xsk_buff_raw_get_data(xs->pool, addr); > > > > > > > > > > + offset =3D offset_in_page(buffer); > > > > > > > > > > + addr =3D buffer - xs->pool->addrs; > > > > > > > > > > + > > > > > > > > > > + for (copied =3D 0, i =3D 0; copied < len; i++) { > > > > > > > > > > + page =3D xs->pool->umem->pgs[addr >> PAGE_SHI= FT]; > > > > > > > > > > + > > > > > > > > > > + get_page(page); > > > > > > > > > > + > > > > > > > > > > + copy =3D min_t(u32, PAGE_SIZE - offset, len -= copied); > > > > > > > > > > + > > > > > > > > > > + skb_fill_page_desc(skb, i, page, offset, copy= ); > > > > > > > > > > + > > > > > > > > > > + copied +=3D copy; > > > > > > > > > > + addr +=3D copy; > > > > > > > > > > + offset =3D 0; > > > > > > > > > > + } > > > > > > > > > > + > > > > > > > > > > + skb->len +=3D len; > > > > > > > > > > + skb->data_len +=3D len; > > > > > > > > > > > > > > > > > > > + skb->truesize +=3D 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 +=3D 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 +=3D 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 account= ing. > > > > > > But in this code, no kernel memory has been allocated (apart fr= om 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 sh= ould > > > > > > 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 othe= r 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 i= t > > > > > 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, especia= lly > > > > > 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 +=3D 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. >=20 > 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. Ah, unaligned mode, sure. Thanks for explanation! Right, we need the loop and skb->truesize +=3D xs->pool->chunk_size * i then. > > > 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 |=3D SKBFL_SHARED_FRAG; > > > > > > skb->len +=3D copy; > > > skb->data_len +=3D copy; > > > skb->truesize +=3D 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