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[87.59.106.155]) by smtp.gmail.com with ESMTPSA id t30sm173712lfg.289.2021.09.09.04.49.56 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Thu, 09 Sep 2021 04:49:56 -0700 (PDT) From: Jesper Dangaard Brouer X-Google-Original-From: Jesper Dangaard Brouer Cc: brouer@redhat.com, ast@kernel.org, daniel@iogearbox.net, hawk@kernel.org, john.fastabend@gmail.com, netdev@vger.kernel.org, linux-kernel@vger.kernel.org, bpf@vger.kernel.org Subject: Re: [PATCH net 0/2] sfc: fallback for lack of xdp tx queues To: =?UTF-8?B?w43DsWlnbyBIdWd1ZXQ=?= , ecree.xilinx@gmail.com, habetsm.xilinx@gmail.com, davem@davemloft.net, kuba@kernel.org, Ivan Babrou , Marek Majkowski , Jakub Sitnicki , Toke Hoiland Jorgensen , Freysteinn Alfredsson References: <20210909092846.18217-1-ihuguet@redhat.com> Message-ID: Date: Thu, 9 Sep 2021 13:49:55 +0200 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:78.0) Gecko/20100101 Thunderbird/78.11.0 MIME-Version: 1.0 In-Reply-To: <20210909092846.18217-1-ihuguet@redhat.com> Content-Type: text/plain; charset=utf-8; format=flowed Content-Language: en-US Content-Transfer-Encoding: 8bit Precedence: bulk List-ID: X-Mailing-List: bpf@vger.kernel.org Great work Huguet, patches LGTM, I would ACK but they have already been applied: Here is the summary with links: - [net,1/2] sfc: fallback for lack of xdp tx queues https://git.kernel.org/netdev/net/c/415446185b93 - [net,2/2] sfc: last resort fallback for lack of xdp tx queues https://git.kernel.org/netdev/net/c/6215b608a8c4 Cloudflare (cc) heads-up for these improvements. And heads-up to Toke and Frey on patch 2/2, as it creates push-back via TX queue stop/restart logic (see kernel API netif_tx_queue_stopped). XDP currently doesn't handle this well, but I hope to see XDP queueing work from your side to improve the situation ;-) On 09/09/2021 11.28, Íñigo Huguet wrote: > If there are not enough hardware resources to allocate one tx queue per > CPU for XDP, XDP_TX and XDP_REDIRECT actions were unavailable, and using > them resulted each time with the packet being drop and this message in > the logs: XDP TX failed (-22) > > These patches implement 2 fallback solutions for 2 different situations > that might happen: > 1. There are not enough free resources for all the tx queues, but there > are some free resources available > 2. There are not enough free resources at all for tx queues. > > Both solutions are based in sharing tx queues, using __netif_tx_lock for > synchronization. In the second case, as there are not XDP TX queues to > share, network stack queues are used instead, but since we're taking > __netif_tx_lock, concurrent access to the queues is correctly protected. > > The solution for this second case might affect performance both of XDP > traffic and normal traffice due to lock contention if both are used > intensively. That's why I call it a "last resort" fallback: it's not a > desirable situation, but at least we have XDP TX working. > > Some tests has shown good results and indicate that the non-fallback > case is not being damaged by this changes. They are also promising for > the fallback cases. This is the test: > 1. From another machine, send high amount of packets with pktgen, script > samples/pktgen/pktgen_sample04_many_flows.sh > 2. In the tested machine, run samples/bpf/xdp_rxq_info with arguments > "-a XDP_TX --swapmac" and see the results > 3. In the tested machine, run also pktgen_sample04 to create high TX > normal traffic, and see how xdp_rxq_info results vary > > Note that this test doesn't check the worst situations for the fallback > solutions because XDP_TX will only be executed from the same CPUs that > are processed by sfc, and not from every CPU in the system, so the > performance drop due to the highest locking contention doesn't happen. > I'd like to test that, as well, but I don't have access right now to a > proper environment. > > Test results: > > Without doing TX: > Before changes: ~2,900,000 pps > After changes, 1 queues/core: ~2,900,000 pps > After changes, 2 queues/core: ~2,900,000 pps > After changes, 8 queues/core: ~2,900,000 pps > After changes, borrowing from network stack: ~2,900,000 pps > > With multiflow TX at the same time: > Before changes: ~1,700,000 - 2,900,000 pps > After changes, 1 queues/core: ~1,700,000 - 2,900,000 pps > After changes, 2 queues/core: ~1,700,000 pps > After changes, 8 queues/core: ~1,700,000 pps > After changes, borrowing from network stack: 1,150,000 pps > > Sporadic "XDP TX failed (-5)" warnings are shown when running xdp program > and pktgen simultaneously. This was expected because XDP doesn't have any > buffering system if the NIC is under very high pressure. Thousands of > these warnings are shown in the case of borrowing net stack queues. As I > said before, this was also expected. > > > Íñigo Huguet (2): > sfc: fallback for lack of xdp tx queues > sfc: last resort fallback for lack of xdp tx queues > > drivers/net/ethernet/sfc/efx_channels.c | 98 ++++++++++++++++++------- > drivers/net/ethernet/sfc/net_driver.h | 8 ++ > drivers/net/ethernet/sfc/tx.c | 29 ++++++-- > 3 files changed, 99 insertions(+), 36 deletions(-) >