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=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 4700FC433B4 for ; Thu, 22 Apr 2021 18:02:25 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 059C2613D8 for ; Thu, 22 Apr 2021 18:02:24 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S236827AbhDVSC6 (ORCPT ); Thu, 22 Apr 2021 14:02:58 -0400 Received: from us-smtp-delivery-124.mimecast.com ([170.10.133.124]:37185 "EHLO us-smtp-delivery-124.mimecast.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S236287AbhDVSC6 (ORCPT ); Thu, 22 Apr 2021 14:02:58 -0400 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1619114543; 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: in-reply-to:in-reply-to:references:references; bh=UiSCDWiCcxogQPyM41lba/4yMV2E3N32U8ri3J8j1cM=; b=Q/LtmRtnZRDXhHBlPxK6Mf4Nj6dJS683aO+/ip7uFRcpOvt/O9/Xsux0zuCZ8OZKSuvoq3 3ZgqKt2YFVMAnNCDZhTpmqtmuEfUuuc03j4oQVJ+B9RPa6VhQ0otoqJgWu4kQ2N9Eaop8v B0Nj8JA2M/L1mTtyPh0f17BgOliQiaw= Received: from mail-ed1-f70.google.com (mail-ed1-f70.google.com [209.85.208.70]) (Using TLS) by relay.mimecast.com with ESMTP id us-mta-250-Q70YJdgsMGCuy5Sbdyn5pg-1; Thu, 22 Apr 2021 14:02:21 -0400 X-MC-Unique: Q70YJdgsMGCuy5Sbdyn5pg-1 Received: by mail-ed1-f70.google.com with SMTP id cz7-20020a0564021ca7b02903853d41d8adso7901989edb.17 for ; Thu, 22 Apr 2021 11:02:21 -0700 (PDT) X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20161025; h=x-gm-message-state:from:to:cc:subject:in-reply-to:references:date :message-id:mime-version; bh=UiSCDWiCcxogQPyM41lba/4yMV2E3N32U8ri3J8j1cM=; b=Uhipe2CvUWEmAfEZkb99t3msiwsgsJS3mOyzB4VtdiH798EY+GN70Fd5WMpJSflls5 s/5OLUYdx7kk39RIvIeXVn1YqvO2wEooqIspz1AZeukg2J7xuEd9BohTjNcqWGOCluEz ddkxE8MXpGetgurrzT+m/+j3+mGvzxToWch1xxQe9lR4Lxr0O/Axy1q4iLX1SngCVk52 h0stdRhhBdNkHW1vLP27uxc99pGdeuEQjK9Mn1VlKx/8Wa6dH7+oBO68x8saLFc0716I /gF/Y5uu3c59pf7wA2cSVWuP+brv6N1X4bA1yOXn73GFU+pXrszZrNzjfNyL1rXRUU0f +itg== X-Gm-Message-State: AOAM5321Zb+Cw8UwE0wgbNGzdCzX3lBqViIY078nZszxwTZnO5MWKNDR fH4u8R5dZ4gVsKoYygu3MLzaa1KM+Qmk7cXwnQrkA46b5q+EkEl89D8iwpCHqu4OXjxed5auTw/ 2uN//n+sCFsoC X-Received: by 2002:a17:906:e4b:: with SMTP id q11mr4754951eji.540.1619114540132; Thu, 22 Apr 2021 11:02:20 -0700 (PDT) X-Google-Smtp-Source: ABdhPJx8XKaKia5stbB08EnaxvjcY2SollztTAf5E7LHRtMtWSlkj9DA9wbjv4tm+Ea1zUBL92lcmw== X-Received: by 2002:a17:906:e4b:: with SMTP id q11mr4754911eji.540.1619114539666; Thu, 22 Apr 2021 11:02:19 -0700 (PDT) Received: from alrua-x1.borgediget.toke.dk ([2a0c:4d80:42:443::2]) by smtp.gmail.com with ESMTPSA id he35sm2333304ejc.2.2021.04.22.11.02.18 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Thu, 22 Apr 2021 11:02:18 -0700 (PDT) Received: by alrua-x1.borgediget.toke.dk (Postfix, from userid 1000) id 538D2180675; Thu, 22 Apr 2021 20:02:18 +0200 (CEST) From: Toke =?utf-8?Q?H=C3=B8iland-J=C3=B8rgensen?= To: Jesper Dangaard Brouer , Hangbin Liu Cc: 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 In-Reply-To: <20210422185332.3199ca2e@carbon> References: <20210422071454.2023282-1-liuhangbin@gmail.com> <20210422071454.2023282-3-liuhangbin@gmail.com> <20210422185332.3199ca2e@carbon> X-Clacks-Overhead: GNU Terry Pratchett Date: Thu, 22 Apr 2021 20:02:18 +0200 Message-ID: <87a6pqfb9x.fsf@toke.dk> MIME-Version: 1.0 Content-Type: text/plain Precedence: bulk List-ID: X-Mailing-List: bpf@vger.kernel.org Jesper Dangaard Brouer writes: > On Thu, 22 Apr 2021 15:14:52 +0800 > Hangbin Liu wrote: > >> 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 > [...] >> 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, struct xdp_buff *xdp, >> enum bpf_map_type map_type = ri->map_type; >> void *fwd = ri->tgt_value; >> u32 map_id = ri->map_id; >> + struct bpf_map *map; >> int err; >> >> ri->map_id = 0; /* Valid map id idr range: [1,INT_MAX[ */ >> @@ -3942,7 +3960,12 @@ int xdp_do_redirect(struct net_device *dev, struct xdp_buff *xdp, >> case BPF_MAP_TYPE_DEVMAP: >> fallthrough; >> case BPF_MAP_TYPE_DEVMAP_HASH: >> - err = dev_map_enqueue(fwd, xdp, dev); >> + map = xchg(&ri->map, NULL); > > Hmm, this looks dangerous for performance to have on this fast-path. > The xchg call can be expensive, AFAIK this is an atomic operation. 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: + map = READ_ONCE(ri->map); + if (map) { + WRITE_ONCE(ri->map, NULL); + err = dev_map_enqueue_multi(xdp, dev, map, + ri->flags & BPF_F_EXCLUDE_INGRESS); + } else { + err = dev_map_enqueue(fwd, xdp, dev); + } (and the same for the generic-XDP path, of course) -Toke