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Wed, 03 Jul 2024 15:40:56 +0000 Message-ID: Date: Wed, 3 Jul 2024 17:40:55 +0200 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH 2/4] nvme-tcp: align I/O cpu with blk-mq mapping Content-Language: en-US To: Sagi Grimberg , Hannes Reinecke Cc: Christoph Hellwig , Keith Busch , linux-nvme@lists.infradead.org References: <20240703135021.34143-1-hare@kernel.org> <20240703135021.34143-3-hare@kernel.org> <11c0b02b-03a3-4097-948b-651b14baa0cf@suse.de> <9bc9d94f-a129-4c6e-ac9e-d0eb8db341b0@grimberg.me> From: Hannes Reinecke In-Reply-To: <9bc9d94f-a129-4c6e-ac9e-d0eb8db341b0@grimberg.me> Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 8bit X-Spamd-Result: default: False [-4.29 / 50.00]; BAYES_HAM(-3.00)[100.00%]; NEURAL_HAM_LONG(-1.00)[-1.000]; NEURAL_HAM_SHORT(-0.20)[-1.000]; MIME_GOOD(-0.10)[text/plain]; XM_UA_NO_VERSION(0.01)[]; RCVD_VIA_SMTP_AUTH(0.00)[]; MIME_TRACE(0.00)[0:+]; TO_DN_SOME(0.00)[]; MID_RHS_MATCH_FROM(0.00)[]; ARC_NA(0.00)[]; RCVD_TLS_ALL(0.00)[]; DKIM_SIGNED(0.00)[suse.de:s=susede2_rsa,suse.de:s=susede2_ed25519]; FUZZY_BLOCKED(0.00)[rspamd.com]; FROM_HAS_DN(0.00)[]; RCPT_COUNT_FIVE(0.00)[5]; FROM_EQ_ENVFROM(0.00)[]; TO_MATCH_ENVRCPT_ALL(0.00)[]; RCVD_COUNT_TWO(0.00)[2]; DBL_BLOCKED_OPENRESOLVER(0.00)[suse.de:email] X-CRM114-Version: 20100106-BlameMichelson ( TRE 0.8.0 (BSD) ) MR-646709E3 X-CRM114-CacheID: sfid-20240703_084059_941347_7DED8D09 X-CRM114-Status: GOOD ( 25.00 ) 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 7/3/24 17:03, Sagi Grimberg wrote: > > > On 03/07/2024 17:53, Hannes Reinecke wrote: >> On 7/3/24 16:19, Sagi Grimberg wrote: >>> >>> >>> On 03/07/2024 16:50, Hannes Reinecke wrote: >>>> When 'wq_unbound' is selected we should select the >>>> the first CPU from a given blk-mq hctx mapping to queue >>>> the tcp workqueue item. With this we can instruct the >>>> workqueue code to keep the I/O affinity and avoid >>>> a performance penalty. >>> >>> wq_unbound is designed to keep io_cpu to be UNBOUND, my recollection >>> was the the person introducing it was trying to make the io_cpu >>> always be on a specific NUMA node, or a subset of cpus within a numa node. So >>> he uses that and tinkers with wq cpumask via sysfs. >>> >>> I don't see why you are tying this to wq_unbound in the first place. >>> >> Because in the default case the workqueue is nailed to a cpu, and will >> not move from it. IE if you call 'queue_work_on()' it _will_ run on >> that cpu. >> But if something else is running on that CPU (printk logging, say), >> you will have to stand in the queue until the scheduler gives you some >> time. >> >> If the workqueue is unbound the workqueue code is able to switch away >> from the cpu if it finds it busy or otherwise unsuitable, leading to a >> better utilization and avoiding a workqueue stall. >> And in the 'unbound' case the 'cpu' argument merely serves as a hint >> where to place the workqueue item. >> At least, that's how I understood the code. > > We should make the io_cpu come from blk-mq hctx mapping by default, and > for every controller it should use a different cpu from the hctx > mapping. That is the default behavior. in the wq_unbound case, we skip > all of that and make io_cpu = WORK_CPU_UNBOUND, as it was before. > > I'm not sure I follow your logic. > Hehe. That's quite simple: there is none :-) I have been tinkering with that approach in the last weeks, but got consistently _worse_ results than with the original implementation. So I gave up on trying to make that the default. >> >> And it makes the 'CPU hogged' messages go away, which is a bonus in >> itself... > > Which messages? aren't these messages saying that the work spent too > much time? why are you describing the case where the work does not get > cpu quota to run? I means these messages: workqueue: nvme_tcp_io_work [nvme_tcp] hogged CPU for >10000us 32771 times, consider switching to WQ_UNBOUND which I get consistently during testing with the default implementation. Cheers, Hannes -- Dr. Hannes Reinecke Kernel Storage Architect hare@suse.de +49 911 74053 688 SUSE Software Solutions GmbH, Frankenstr. 146, 90461 Nürnberg HRB 36809 (AG Nürnberg), GF: I. Totev, A. McDonald, W. Knoblich