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[146.241.12.146]) by smtp.gmail.com with ESMTPSA id ffacd0b85a97d-3912c103f57sm18734500f8f.91.2025.03.11.10.24.36 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Tue, 11 Mar 2025 10:24:37 -0700 (PDT) Message-ID: <8a47efb6-ee87-4287-b61b-eff37421609f@redhat.com> Date: Tue, 11 Mar 2025 18:24:36 +0100 Precedence: bulk X-Mailing-List: netdev@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v3 net-next 2/2] udp_tunnel: use static call for GRO hooks when possible To: Willem de Bruijn , netdev@vger.kernel.org Cc: "David S. Miller" , Eric Dumazet , Jakub Kicinski , Simon Horman , David Ahern , kuniyu@amazon.com References: <67cfa5236c212_28a0b329453@willemb.c.googlers.com.notmuch> Content-Language: en-US From: Paolo Abeni In-Reply-To: <67cfa5236c212_28a0b329453@willemb.c.googlers.com.notmuch> Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit On 3/11/25 3:51 AM, Willem de Bruijn wrote: > Paolo Abeni wrote: [...] >> +void udp_tunnel_update_gro_rcv(struct sock *sk, bool add) >> +{ >> + struct udp_tunnel_type_entry *cur = NULL, *avail = NULL; >> + struct udp_sock *up = udp_sk(sk); >> + int i, old_gro_type_nr; >> + >> + if (!up->gro_receive) >> + return; >> + >> + mutex_lock(&udp_tunnel_gro_type_lock); >> + for (i = 0; i < UDP_MAX_TUNNEL_TYPES; i++) { >> + if (!refcount_read(&udp_tunnel_gro_types[i].count)) > > Optionally: && !avail, to fill the list from the front. And on delete > avoid gaps. For instance, like __fanout_link/__fanout_unlink. > > Can stop sooner then. And list length is then implicit as i once found > the first [i].count == zero. > > Then again, this list is always short. I can imagine you prefer to > leave as is. I avoided optimizations for this slow path, to keep the code simpler. Thinking again about it, avoiding gaps will simplify/cleanup the code a bit (no need to lookup the enabled tunnel on deletion and to use `avail` on addition), so I'll do it. Note that I'll still need to explicitly track the number of enabled tunnel types, as an easy way to disable the static call in the unlikely udp_tunnel_gro_type_nr == UDP_MAX_TUNNEL_TYPES event. [...] >> + if (udp_tunnel_gro_type_nr == 1) { >> + for (i = 0; i < UDP_MAX_TUNNEL_TYPES; i++) { >> + cur = &udp_tunnel_gro_types[i]; >> + if (refcount_read(&cur->count)) { >> + static_call_update(udp_tunnel_gro_rcv, >> + cur->gro_receive); >> + static_branch_enable(&udp_tunnel_static_call); >> + } >> + } >> + } else if (old_gro_type_nr == 1) { >> + static_branch_disable(&udp_tunnel_static_call); >> + static_call_update(udp_tunnel_gro_rcv, dummy_gro_rcv); > > These operations must not be reorderd, or dummy_gro_rcv might get hit. > > If static calls are not configured, the last call is just a > WRITE_ONCE. Similar for static_branch_disable if !CONFIG_JUMP_LABEL. When both construct are disabled, I think a wmb/rmb pair would be needed to ensure no reordering, and that in turn looks overkill. I think it would be better just drop the WARN_ONCE in dummy_gro_rcv(). /P