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([2600:1700:65a0:78e0:514:7862:1503:8e4d]) by smtp.gmail.com with ESMTPSA id y3sm3012481wrw.83.2019.09.20.10.09.49 (version=TLS1_2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Fri, 20 Sep 2019 10:09:52 -0700 (PDT) Subject: Re: [PATCH 1/4] softirq: implement IRQ flood detection mechanism To: Ming Lei References: <6f3b6557-1767-8c80-f786-1ea667179b39@acm.org> <2a8bd278-5384-d82f-c09b-4fce236d2d95@linaro.org> <20190905090617.GB4432@ming.t460p> <6a36ccc7-24cd-1d92-fef1-2c5e0f798c36@linaro.org> <20190906014819.GB27116@ming.t460p> <6eb2a745-7b92-73ce-46f5-cc6a5ef08abc@grimberg.me> <20190907000100.GC12290@ming.t460p> <20190918143732.GA19364@ming.t460p> From: Sagi Grimberg Message-ID: <1f01c041-cc6e-e27e-7691-63c903d1fed7@grimberg.me> Date: Fri, 20 Sep 2019 10:09:47 -0700 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:60.0) Gecko/20100101 Thunderbird/60.8.0 MIME-Version: 1.0 In-Reply-To: <20190918143732.GA19364@ming.t460p> Content-Language: en-US X-CRM114-Version: 20100106-BlameMichelson ( TRE 0.8.0 (BSD) ) MR-646709E3 X-CRM114-CacheID: sfid-20190920_100954_761822_C12194D3 X-CRM114-Status: GOOD ( 14.61 ) X-BeenThere: linux-nvme@lists.infradead.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: Jens Axboe , Hannes Reinecke , John Garry , Bart Van Assche , linux-scsi@vger.kernel.org, Peter Zijlstra , Long Li , Daniel Lezcano , LKML , linux-nvme@lists.infradead.org, Keith Busch , Ingo Molnar , Thomas Gleixner , Christoph Hellwig Content-Transfer-Encoding: 7bit Content-Type: text/plain; charset="us-ascii"; Format="flowed" Sender: "Linux-nvme" Errors-To: linux-nvme-bounces+linux-nvme=archiver.kernel.org@lists.infradead.org >> It seems like we're attempting to stay in irq context for as long as we >> can instead of scheduling to softirq/thread context if we have more than >> a minimal amount of work to do. Without at least understanding why >> softirq/thread degrades us so much this code seems like the wrong >> approach to me. Interrupt context will always be faster, but it is >> not a sufficient reason to spend as much time as possible there, is it? > > If extra latency is added in IO completion path, this latency will be > introduced in the submission path, because the hw queue depth is fixed, > which is often small. Especially in case of multiple submission vs. > single(shared) completion, the whole hw queue tags can be exhausted > easily. This is why the patch is reaping the first batch from hard-irq, but only if it has more will defer to softirq. So I'm not sure the short QD use case applies here... > I guess no such effect for networking IO. Maybe, maybe not... _______________________________________________ Linux-nvme mailing list Linux-nvme@lists.infradead.org http://lists.infradead.org/mailman/listinfo/linux-nvme