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 4FC6FC433E6 for ; Tue, 26 Jan 2021 19:42:32 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 28418207BC for ; Tue, 26 Jan 2021 19:42:32 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S2388012AbhAZFha (ORCPT ); Tue, 26 Jan 2021 00:37:30 -0500 Received: from mail-40133.protonmail.ch ([185.70.40.133]:38594 "EHLO mail-40133.protonmail.ch" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1728778AbhAYN2B (ORCPT ); Mon, 25 Jan 2021 08:28:01 -0500 Date: Mon, 25 Jan 2021 13:25:45 +0000 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=pm.me; s=protonmail; t=1611581149; bh=tdGcVh9gs/Ps1kaCgb3Io6wNV3WCHqwcSbRKjKiNX4c=; h=Date:To:From:Cc:Reply-To:Subject:In-Reply-To:References:From; b=jz5MsAYDpiMp5M1RxMFnbBNVzOyW9jSsztIixvbUlfNQcmd2HOSBXz2trdV+YYEp1 76TRSQqTJ5GLShJU7GlrcA/wbutjDffgd3OBkMtOOuJc/sSBj2OC58V3PKLwTz93+h zipXtl+jksdW+ZbpreipviK4oiV68XkZ/Dyh8tfPeMWEbokWDD+Ngcti8jcUCwJRS9 HBSLDdS7ALSsiXLMpFwfHFmDA29uSsis+Xhnz/j7rG5SzHQihtQX1BzVj71bx09t2k xxitF8gPqWpw1syJJE3M0RnuprHWbs5Vd86lYRoznlAWLHuRiZzn7MHhLxa0gB1p+C J8ju3Jd0nPLog== To: Xuan Zhuo From: Alexander Lobakin Cc: Alexander Lobakin , Eric Dumazet , "Michael S. Tsirkin" , Jason Wang , "David S. Miller" , Jakub Kicinski , bjorn@kernel.org, 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@vger.kernel.org, netdev@vger.kernel.org, linux-kernel@vger.kernel.org Reply-To: Alexander Lobakin Subject: Re: [PATCH bpf-next v3 3/3] xsk: build skb by page Message-ID: <20210125132502.3165-1-alobakin@pm.me> In-Reply-To: <1611544243.8363645-1-xuanzhuo@linux.alibaba.com> References: <1611544243.8363645-1-xuanzhuo@linux.alibaba.com> 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: Xuan Zhuo Date: Mon, 25 Jan 2021 11:10:43 +0800 > On Fri, 22 Jan 2021 16:24:17 +0000, Alexander Lobakin wr= ote: > > From: Xuan Zhuo > > Date: Fri, 22 Jan 2021 23:36:29 +0800 > > > > > On Fri, 22 Jan 2021 12:08:00 +0000, Alexander Lobakin wrote: > > > > From: Alexander Lobakin > > > > Date: Fri, 22 Jan 2021 11:55:35 +0000 > > > > > > > > > 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 m= emory 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, i= t 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) > > > > > > > > =09sock_wfree(skb); > > > > > > > > } > > > > > > > > > > > > > > > > +static struct sk_buff *xsk_build_skb_zerocopy(struct xdp_s= ock *xs, > > > > > > > > +=09=09=09=09=09 struct xdp_desc *desc) > > > > > > > > +{ > > > > > > > > +=09u32 len, offset, copy, copied; > > > > > > > > +=09struct sk_buff *skb; > > > > > > > > +=09struct page *page; > > > > > > > > +=09void *buffer; > > > > > > > > +=09int err, i; > > > > > > > > +=09u64 addr; > > > > > > > > + > > > > > > > > +=09skb =3D sock_alloc_send_skb(&xs->sk, 0, 1, &err); > > > > > > > > Also, > > > > maybe we should allocate it with NET_SKB_PAD so NIC drivers could > > > > use some reserved space? > > > > > > > > =09=09skb =3D sock_alloc_send_skb(&xs->sk, NET_SKB_PAD, 1, &err); > > > > =09=09... > > > > =09=09skb_reserve(skb, NET_SKB_PAD); > > > > > > > > Eric, what do you think? > > > > > > I think you are right. Some space should be added to continuous equip= ment. This > > > space should also be added in the copy mode below. Is LL_RESERVED_SPA= CE more > > > appropriate? > > > > No. If you look at __netdev_alloc_skb() and __napi_alloc_skb(), they > > reserve NET_SKB_PAD at the beginning of linear area. Documentation of > > __build_skb() also says that driver should reserve NET_SKB_PAD before > > the actual frame, so it is a standartized hardware-independent > > headroom. >=20 > I understand that these scenarios are in the case of receiving packets, a= nd the > increased space is used by the protocol stack, especially RPS. I don't kn= ow if > this also applies to the sending scenario? >=20 > > Leaving that space in skb->head will allow developers to implement > > IFF_TX_SKB_NO_LINEAR in a wider variety of drivers, especially when > > a driver has to prepend some sort of data before the actual frame. > > Since it's usually of a size of one cacheline, shouldn't be a big > > deal. > > >=20 > I agree with this. Some network cards require some space. For example, > virtio-net needs to add a virtio_net_hdr_mrg_rxbuf before skb->data, so m= y > original understanding is used here. When we send the skb to the > driver, the driver may need a memory space. So I refer to the > implementation of __ip_append_data, I feel that adding > LL_RESERVED_SPACE is a suitable solution. >=20 > I feel that I may still not understand the use scene you mentioned. Can y= ou > elaborate on what you understand this space will be used for? LL_RESERVED_SPACE() consists of L2 header size (Ethernet for the most cases) and dev->needed_headroom. That is not a value to count on, as: - L2 header is already here in XSK buffer; - not all drivers set dev->needed_headroom; - it's aligned by 16, not L1_CACHE_SIZE. As this path is XSK generic path, i.e. when driver-side XSK is not present or not requested, it can be applied to every driver. Many of them call skb_cow_head() + skb_push() on their xmit path: - nearly all virtual drivers (to insert their specific headers); - nearly all switch drivers (to insert switch CPU port tags); - some enterprise NIC drivers (ChelsIO for LSO, Netronome for TLS etc.). skb_cow_head() + skb_push() relies on a required NET_SKB_PAD headroom. In case where there is no enough space (and you allocate an skb with no headroom at all), skb will be COWed, which is a huge overhead and will cause slowdowns. So, adding NET_SKB_PAD would save from almost all, if not all, such reallocations. > Thanks. >=20 > > > > [ I also had an idea of allocating an skb with a headroom of > > NET_SKB_PAD + 256 bytes, so nearly all drivers could just call > > pskb_pull_tail() to support such type of skbuffs without much > > effort, but I think that it's better to teach drivers to support > > xmitting of really headless ones. If virtio_net can do it, why > > shouldn't the others ] > > > > > > > > > > +=09if (unlikely(!skb)) > > > > > > > > +=09=09return ERR_PTR(err); > > > > > > > > + > > > > > > > > +=09addr =3D desc->addr; > > > > > > > > +=09len =3D desc->len; > > > > > > > > + > > > > > > > > +=09buffer =3D xsk_buff_raw_get_data(xs->pool, addr); > > > > > > > > +=09offset =3D offset_in_page(buffer); > > > > > > > > +=09addr =3D buffer - xs->pool->addrs; > > > > > > > > + > > > > > > > > +=09for (copied =3D 0, i =3D 0; copied < len; i++) { > > > > > > > > +=09=09page =3D xs->pool->umem->pgs[addr >> PAGE_SHIFT]; > > > > > > > > + > > > > > > > > +=09=09get_page(page); > > > > > > > > + > > > > > > > > +=09=09copy =3D min_t(u32, PAGE_SIZE - offset, len - copied= ); > > > > > > > > + > > > > > > > > +=09=09skb_fill_page_desc(skb, i, page, offset, copy); > > > > > > > > + > > > > > > > > +=09=09copied +=3D copy; > > > > > > > > +=09=09addr +=3D copy; > > > > > > > > +=09=09offset =3D 0; > > > > > > > > +=09} > > > > > > > > + > > > > > > > > +=09skb->len +=3D len; > > > > > > > > +=09skb->data_len +=3D len; > > > > > > > > > > > > > > > +=09skb->truesize +=3D len; > > > > > > > > > > > > > > This is not the truesize, unfortunately. > > > > > > > > > > > > > > We need to account for the number of pages, not number of byt= es. > > > > > > > > > > > > The easiest solution is: > > > > > > > > > > > > =09skb->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 > > > > > > > > > > =09skb->truesize +=3D PAGE_SIZE * npages; > > > > > > > > > > Right. > > > > > > > > > > > > > + > > > > > > > > +=09refcount_add(len, &xs->sk.sk_wmem_alloc); > > > > > > > > + > > > > > > > > +=09return skb; > > > > > > > > +} > > > > > > > > + > > > > > > > > > > > > Al > > > > > > > > > > Thanks, > > > > > Al > > > > > > > > Al Thanks, Al