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[85.65.198.251]) by smtp.gmail.com with ESMTPSA id ffacd0b85a97d-3675a0cdc5csm16607718f8f.18.2024.07.03.12.41.39 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Wed, 03 Jul 2024 12:41:39 -0700 (PDT) Message-ID: Date: Wed, 3 Jul 2024 22:41:38 +0300 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH 1/4] nvme-tcp: per-controller I/O workqueues To: Tejun Heo Cc: Hannes Reinecke , Hannes Reinecke , Christoph Hellwig , Keith Busch , linux-nvme@lists.infradead.org References: <20240703135021.34143-1-hare@kernel.org> <20240703135021.34143-2-hare@kernel.org> <7e4444d0-f156-439e-9363-4beb86bb6248@grimberg.me> Content-Language: en-US From: Sagi Grimberg In-Reply-To: Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit X-CRM114-Version: 20100106-BlameMichelson ( TRE 0.8.0 (BSD) ) MR-646709E3 X-CRM114-CacheID: sfid-20240703_124142_034884_6F6F02C4 X-CRM114-Status: GOOD ( 13.33 ) X-BeenThere: linux-nvme@lists.infradead.org X-Mailman-Version: 2.1.34 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Sender: "Linux-nvme" Errors-To: linux-nvme-bounces+linux-nvme=archiver.kernel.org@lists.infradead.org On 03/07/2024 22:17, Tejun Heo wrote: > Hello, > > On Wed, Jul 03, 2024 at 10:14:14PM +0300, Sagi Grimberg wrote: > ... >> None of these reasons are the claimed reason to use separate workqueues in >> this patch. The claim is that it is more efficient, i.e. has less overhead. >> >> The commit msg is the following: >> "Implement per-controller I/O workqueues to reduce workqueue contention >> during I/O." > Hmm... it's not impossible for the concurrency accounting in pool_workqueues > to show up if the issue rate is *really* high but I'd be surprised if that > actually matters given that the backend pool is shared. Maybe I'm missing > something but I don't see a reason why multiple workqueues would be more > efficient than a shared one. That was my assumption as well, that there is no real point in using multiple workqueues. And hence my surprise. Hannes, can you please provide a quantitive improvement that you saw simply by separating to different workqueues?