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[80.5.128.40]) by smtp.gmail.com with ESMTPSA id k18sm6095339wrd.45.2020.12.16.15.12.12 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Wed, 16 Dec 2020 15:12:13 -0800 (PST) Subject: Re: [PATCH net-next] sfc: reduce the number of requested xdp ev queues To: Jesper Dangaard Brouer Cc: Ivan Babrou , netdev@vger.kernel.org, linux-kernel@vger.kernel.org, bpf@vger.kernel.org, kernel-team@cloudflare.com, Martin Habets , "David S. Miller" , Jakub Kicinski , Alexei Starovoitov , Daniel Borkmann , Jesper Dangaard Brouer , John Fastabend , Marek Majtyka References: <20201215012907.3062-1-ivan@cloudflare.com> <20201215104327.2be76156@carbon> <205ba636-f180-3003-a41c-828e1fe1a13b@gmail.com> <20201216094524.0c6e521c@carbon> From: Edward Cree Message-ID: <2438e8ee-99ad-167d-d00c-fc208ba7caa9@gmail.com> Date: Wed, 16 Dec 2020 23:12:12 +0000 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:78.0) Gecko/20100101 Thunderbird/78.5.0 MIME-Version: 1.0 In-Reply-To: <20201216094524.0c6e521c@carbon> Content-Type: text/plain; charset=utf-8 Content-Language: en-GB Content-Transfer-Encoding: 7bit Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 16/12/2020 08:45, Jesper Dangaard Brouer wrote: > So, what I hear is that this fix is just pampering over the real issue. Yes, it is, but it's better than nothing in the meantime while we work out the complete fix. > I suggest that you/we detect the situation, and have a code path that > will take a lock (per 16 packets bulk) and solve the issue. Imho that would _also_ paper over the issue, because it would mean the system degraded to a lower performance mode of operation, while still appearing to support XDP_TX. I think that that in general should not happen unless there is a way for the user to determine at runtime whether it has/should happen. Perhaps Marek's new XDP feature flags could include a "tx-lockless" flag to indicate this? -ed