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[85.204.121.218]) by smtp.gmail.com with ESMTPSA id l19sm3806147edb.50.2019.10.08.02.04.01 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Tue, 08 Oct 2019 02:04:01 -0700 (PDT) Received: by alrua-x1.borgediget.toke.dk (Postfix, from userid 1000) id B884C18063D; Tue, 8 Oct 2019 11:04:00 +0200 (CEST) From: Toke =?utf-8?Q?H=C3=B8iland-J=C3=B8rgensen?= To: =?utf-8?B?QmrDtnJuIFTDtnBlbA==?= Cc: Sridhar Samudrala , "Karlsson\, Magnus" , =?utf-8?B?QmrDtnJuIFTDtnBlbA==?= , Netdev , bpf , intel-wired-lan , maciej.fijalkowski@intel.com, tom.herbert@intel.com Subject: Re: [PATCH bpf-next 2/4] xsk: allow AF_XDP sockets to receive packets directly from a queue In-Reply-To: References: <1570515415-45593-1-git-send-email-sridhar.samudrala@intel.com> <1570515415-45593-3-git-send-email-sridhar.samudrala@intel.com> <875zkzn2pj.fsf@toke.dk> X-Clacks-Overhead: GNU Terry Pratchett Date: Tue, 08 Oct 2019 11:04:00 +0200 Message-ID: <878spvlibj.fsf@toke.dk> MIME-Version: 1.0 X-MC-Unique: c-aObWILPyW5rO4jeMBF2Q-1 X-Mimecast-Spam-Score: 0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: quoted-printable Sender: netdev-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: netdev@vger.kernel.org Bj=C3=B6rn T=C3=B6pel writes: > On Tue, 8 Oct 2019 at 08:59, Toke H=C3=B8iland-J=C3=B8rgensen wrote: >> >> Sridhar Samudrala writes: >> >> > int xdp_do_redirect(struct net_device *dev, struct xdp_buff *xdp, >> > struct bpf_prog *xdp_prog) >> > { >> > struct bpf_redirect_info *ri =3D this_cpu_ptr(&bpf_redirect_info= ); >> > struct bpf_map *map =3D READ_ONCE(ri->map); >> > + struct xdp_sock *xsk; >> > + >> > + xsk =3D xdp_get_direct_xsk(ri); >> > + if (xsk) >> > + return xsk_rcv(xsk, xdp); >> >> This is a new branch and a read barrier in the XDP_REDIRECT fast path. >> What's the performance impact of that for non-XSK redirect? >> > > The dependent-read-barrier in READ_ONCE? Another branch -- leave that > to the branch-predictor already! ;-) No, you're right, performance > impact here is interesting. I guess the same static_branch could be > used here as well... In any case, some measurements to see the impact (or lack thereof) would be useful :) -Toke