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=-10.8 required=3.0 tests=BAYES_00,DKIMWL_WL_HIGH, DKIM_SIGNED,DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS, INCLUDES_PATCH,MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS 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 12FB0C433B4 for ; Fri, 23 Apr 2021 16:55:01 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id E234E61261 for ; Fri, 23 Apr 2021 16:55:00 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S231844AbhDWQzg (ORCPT ); Fri, 23 Apr 2021 12:55:36 -0400 Received: from us-smtp-delivery-124.mimecast.com ([170.10.133.124]:59115 "EHLO us-smtp-delivery-124.mimecast.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S231522AbhDWQzf (ORCPT ); Fri, 23 Apr 2021 12:55:35 -0400 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1619196898; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version:content-type:content-type: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references; bh=wFxz5Zzs7llrIJ0AdPOjAD3crmXIVLE/A0MxWzI0Aeg=; b=Kvu9SUVxn/RaKNnaxBhrXETi+pyo2jhQqaey3qaXvXTyYoVCBWzQjdIiNutqwi4Xe790eO nqgmC+OMZF8JcVfrfVvWgXex3u0yjA68pwFDPmaIb0eJQxqtBOkgebbOAWPLRs9hAo/n6k N2jO6GFLp5MbdDG8z+uCpcreA8vGbvk= Received: from mimecast-mx01.redhat.com (mimecast-mx01.redhat.com [209.132.183.4]) (Using TLS) by relay.mimecast.com with ESMTP id us-mta-514-zQJN5xTOOAaKRbp0h_W9Ew-1; Fri, 23 Apr 2021 12:54:56 -0400 X-MC-Unique: zQJN5xTOOAaKRbp0h_W9Ew-1 Received: from smtp.corp.redhat.com (int-mx08.intmail.prod.int.phx2.redhat.com [10.5.11.23]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mimecast-mx01.redhat.com (Postfix) with ESMTPS id 4FC98107ACCD; Fri, 23 Apr 2021 16:54:54 +0000 (UTC) Received: from carbon (unknown [10.36.110.19]) by smtp.corp.redhat.com (Postfix) with ESMTP id E20E71992D; Fri, 23 Apr 2021 16:54:30 +0000 (UTC) Date: Fri, 23 Apr 2021 18:54:29 +0200 From: Jesper Dangaard Brouer To: Toke =?UTF-8?B?SMO4aWxhbmQtSsO4cmdlbnNlbg==?= Cc: Hangbin Liu , bpf@vger.kernel.org, netdev@vger.kernel.org, Jiri Benc , Eelco Chaudron , ast@kernel.org, Daniel Borkmann , Lorenzo Bianconi , David Ahern , Andrii Nakryiko , Alexei Starovoitov , John Fastabend , Maciej Fijalkowski , =?UTF-8?B?QmrDtnJuIFQ=?= =?UTF-8?B?w7ZwZWw=?= , Martin KaFai Lau , brouer@redhat.com Subject: Re: [PATCHv9 bpf-next 2/4] xdp: extend xdp_redirect_map with broadcast support Message-ID: <20210423185429.126492d0@carbon> In-Reply-To: <87a6pqfb9x.fsf@toke.dk> References: <20210422071454.2023282-1-liuhangbin@gmail.com> <20210422071454.2023282-3-liuhangbin@gmail.com> <20210422185332.3199ca2e@carbon> <87a6pqfb9x.fsf@toke.dk> MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: quoted-printable X-Scanned-By: MIMEDefang 2.84 on 10.5.11.23 Precedence: bulk List-ID: X-Mailing-List: netdev@vger.kernel.org On Thu, 22 Apr 2021 20:02:18 +0200 Toke H=C3=B8iland-J=C3=B8rgensen wrote: > Jesper Dangaard Brouer writes: >=20 > > On Thu, 22 Apr 2021 15:14:52 +0800 > > Hangbin Liu wrote: > > =20 > >> diff --git a/net/core/filter.c b/net/core/filter.c > >> index cae56d08a670..afec192c3b21 100644 > >> --- a/net/core/filter.c > >> +++ b/net/core/filter.c =20 > > [...] =20 > >> int xdp_do_redirect(struct net_device *dev, struct xdp_buff *xdp, > >> struct bpf_prog *xdp_prog) > >> { > >> @@ -3933,6 +3950,7 @@ int xdp_do_redirect(struct net_device *dev, stru= ct xdp_buff *xdp, > >> enum bpf_map_type map_type =3D ri->map_type; > >> void *fwd =3D ri->tgt_value; > >> u32 map_id =3D ri->map_id; > >> + struct bpf_map *map; > >> int err; > >> =20 > >> ri->map_id =3D 0; /* Valid map id idr range: [1,INT_MAX[ */ > >> @@ -3942,7 +3960,12 @@ int xdp_do_redirect(struct net_device *dev, str= uct xdp_buff *xdp, > >> case BPF_MAP_TYPE_DEVMAP: > >> fallthrough; > >> case BPF_MAP_TYPE_DEVMAP_HASH: > >> - err =3D dev_map_enqueue(fwd, xdp, dev); > >> + map =3D xchg(&ri->map, NULL); =20 > > > > Hmm, this looks dangerous for performance to have on this fast-path. > > The xchg call can be expensive, AFAIK this is an atomic operation. =20 >=20 > Ugh, you're right. That's my bad, I suggested replacing the > READ_ONCE()/WRITE_ONCE() pair with the xchg() because an exchange is > what it's doing, but I failed to consider the performance implications > of the atomic operation. Sorry about that, Hangbin! I guess this should > be changed to: >=20 > + map =3D READ_ONCE(ri->map); > + if (map) { > + WRITE_ONCE(ri->map, NULL); > + err =3D dev_map_enqueue_multi(xdp, dev, map, > + ri->flags & BPF_F_EXCLUDE_INGRESS); > + } else { > + err =3D dev_map_enqueue(fwd, xdp, dev); > + } This is highly sensitive fast-path code, as you saw Bj=C3=B8rn have been hunting nanosec in this area. The above code implicitly have "map" as the likely option, which I don't think it is. > (and the same for the generic-XDP path, of course) >=20 > -Toke >=20 --=20 Best regards, Jesper Dangaard Brouer MSc.CS, Principal Kernel Engineer at Red Hat LinkedIn: http://www.linkedin.com/in/brouer