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[2.104.116.184]) by smtp.gmail.com with ESMTPSA id i22-20020a2e8096000000b00250664c906asm2972324ljg.133.2022.05.25.01.34.27 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Wed, 25 May 2022 01:34:28 -0700 (PDT) From: Hans Schultz X-Google-Original-From: Hans Schultz To: Nikolay Aleksandrov , Hans Schultz , davem@davemloft.net, kuba@kernel.org Cc: netdev@vger.kernel.org, Andrew Lunn , Vivien Didelot , Florian Fainelli , Vladimir Oltean , Eric Dumazet , Paolo Abeni , Jiri Pirko , Ivan Vecera , Roopa Prabhu , Shuah Khan , Daniel Borkmann , Ido Schimmel , linux-kernel@vger.kernel.org, bridge@lists.linux-foundation.org, linux-kselftest@vger.kernel.org Subject: Re: [PATCH V3 net-next 1/4] net: bridge: add fdb flag to extent locked port feature In-Reply-To: References: <20220524152144.40527-1-schultz.hans+netdev@gmail.com> <20220524152144.40527-2-schultz.hans+netdev@gmail.com> <01e6e35c-f5c9-9776-1263-058f84014ed9@blackwall.org> <86zgj6oqa9.fsf@gmail.com> Date: Wed, 25 May 2022 10:34:27 +0200 Message-ID: <86fskyggdo.fsf@gmail.com> MIME-Version: 1.0 Content-Type: text/plain Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On ons, maj 25, 2022 at 11:06, Nikolay Aleksandrov wrote: > On 24/05/2022 19:21, Hans Schultz wrote: >>> >>> Hi Hans, >>> So this approach has a fundamental problem, f->dst is changed without any synchronization >>> you cannot rely on it and thus you cannot account for these entries properly. We must be very >>> careful if we try to add any new synchronization not to affect performance as well. >>> More below... >>> >>>> @@ -319,6 +326,9 @@ static void fdb_delete(struct net_bridge *br, struct net_bridge_fdb_entry *f, >>>> if (test_bit(BR_FDB_STATIC, &f->flags)) >>>> fdb_del_hw_addr(br, f->key.addr.addr); >>>> >>>> + if (test_bit(BR_FDB_ENTRY_LOCKED, &f->flags) && !test_bit(BR_FDB_OFFLOADED, &f->flags)) >>>> + atomic_dec(&f->dst->locked_entry_cnt); >>> >>> Sorry but you cannot do this for multiple reasons: >>> - f->dst can be NULL >>> - f->dst changes without any synchronization >>> - there is no synchronization between fdb's flags and its ->dst >>> >>> Cheers, >>> Nik >> >> Hi Nik, >> >> if a port is decoupled from the bridge, the locked entries would of >> course be invalid, so maybe if adding and removing a port is accounted >> for wrt locked entries and the count of locked entries, would that not >> work? >> >> Best, >> Hans > > Hi Hans, > Unfortunately you need the correct amount of locked entries per-port if you want > to limit their number per-port, instead of globally. So you need a > consistent Hi Nik, the used dst is a port structure, so it is per-port and not globally. Best, Hans > fdb view with all its attributes when changing its dst in this case, which would > require new locking because you have multiple dependent struct fields and it will > kill roaming/learning scalability. I don't think this use case is worth the complexity it > will bring, so I'd suggest an alternative - you can monitor the number of locked entries > per-port from a user-space agent and disable port learning or some similar solution that > doesn't require any complex kernel changes. Is the limit a requirement to add the feature? > > I have an idea how to do it and to minimize the performance hit if it really is needed > but it'll add a lot of complexity which I'd like to avoid if possible. > > Cheers, > Nik From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmail.com; s=20210112; h=from:to:cc:subject:in-reply-to:references:date:message-id :mime-version; bh=5L0FJw8nrreK+iWXw2F3MaAOrCQpmilHML/7HPSt5+4=; b=azwYnsS6jJEQvSuK4hoXH6WieSqwBE2dO+Bdu6YXtPBvcuUmTfpC2qwzKvfRSAGzKe AywA5P/AgCEHA+hSDE09wNNIxJeazza54hvRtKsM0KHE9XkEoUECPoherZUTjO/quYLX Ia/SRkqrRtnoKqZUnvfJDwwtnDjK4AWeTkS5oTNe/kttqS2+ML3Ah3K8aCLre0PQ/WsB FLtIyd+3n8Ag8VLjPa5MMsnq6nMbmdQGOMUy8F5fLL1tf6aShTHh97UcbwtSsm4BnOQ0 kr5CBdH2eljtkZpg56jZHdcWO1mU1QK+FEeFMv1xX9ebJkDih3+MTRBgbslM8CaHJyNz Ic+w== From: Hans Schultz In-Reply-To: References: <20220524152144.40527-1-schultz.hans+netdev@gmail.com> <20220524152144.40527-2-schultz.hans+netdev@gmail.com> <01e6e35c-f5c9-9776-1263-058f84014ed9@blackwall.org> <86zgj6oqa9.fsf@gmail.com> Date: Wed, 25 May 2022 10:34:27 +0200 Message-ID: <86fskyggdo.fsf@gmail.com> MIME-Version: 1.0 Content-Type: text/plain Subject: Re: [Bridge] [PATCH V3 net-next 1/4] net: bridge: add fdb flag to extent locked port feature List-Id: Linux Ethernet Bridging List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , To: Nikolay Aleksandrov , Hans Schultz , davem@davemloft.net, kuba@kernel.org Cc: Ivan Vecera , Andrew Lunn , Florian Fainelli , Jiri Pirko , Daniel Borkmann , netdev@vger.kernel.org, Ido Schimmel , bridge@lists.linux-foundation.org, linux-kernel@vger.kernel.org, Eric Dumazet , linux-kselftest@vger.kernel.org, Roopa Prabhu , Paolo Abeni , Vladimir Oltean , Shuah Khan , Vivien Didelot On ons, maj 25, 2022 at 11:06, Nikolay Aleksandrov wrote: > On 24/05/2022 19:21, Hans Schultz wrote: >>> >>> Hi Hans, >>> So this approach has a fundamental problem, f->dst is changed without any synchronization >>> you cannot rely on it and thus you cannot account for these entries properly. We must be very >>> careful if we try to add any new synchronization not to affect performance as well. >>> More below... >>> >>>> @@ -319,6 +326,9 @@ static void fdb_delete(struct net_bridge *br, struct net_bridge_fdb_entry *f, >>>> if (test_bit(BR_FDB_STATIC, &f->flags)) >>>> fdb_del_hw_addr(br, f->key.addr.addr); >>>> >>>> + if (test_bit(BR_FDB_ENTRY_LOCKED, &f->flags) && !test_bit(BR_FDB_OFFLOADED, &f->flags)) >>>> + atomic_dec(&f->dst->locked_entry_cnt); >>> >>> Sorry but you cannot do this for multiple reasons: >>> - f->dst can be NULL >>> - f->dst changes without any synchronization >>> - there is no synchronization between fdb's flags and its ->dst >>> >>> Cheers, >>> Nik >> >> Hi Nik, >> >> if a port is decoupled from the bridge, the locked entries would of >> course be invalid, so maybe if adding and removing a port is accounted >> for wrt locked entries and the count of locked entries, would that not >> work? >> >> Best, >> Hans > > Hi Hans, > Unfortunately you need the correct amount of locked entries per-port if you want > to limit their number per-port, instead of globally. So you need a > consistent Hi Nik, the used dst is a port structure, so it is per-port and not globally. Best, Hans > fdb view with all its attributes when changing its dst in this case, which would > require new locking because you have multiple dependent struct fields and it will > kill roaming/learning scalability. I don't think this use case is worth the complexity it > will bring, so I'd suggest an alternative - you can monitor the number of locked entries > per-port from a user-space agent and disable port learning or some similar solution that > doesn't require any complex kernel changes. Is the limit a requirement to add the feature? > > I have an idea how to do it and to minimize the performance hit if it really is needed > but it'll add a lot of complexity which I'd like to avoid if possible. > > Cheers, > Nik