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Mon, 01 Jul 2024 05:16:28 -0400 X-MC-Unique: NPstdspGOHmTb05q43_i_A-1 Received: from mx-prod-int-02.mail-002.prod.us-west-2.aws.redhat.com (mx-prod-int-02.mail-002.prod.us-west-2.aws.redhat.com [10.30.177.15]) (using TLSv1.3 with cipher TLS_AES_256_GCM_SHA384 (256/256 bits) key-exchange X25519 server-signature RSA-PSS (2048 bits) server-digest SHA256) (No client certificate requested) by mx-prod-mc-04.mail-002.prod.us-west-2.aws.redhat.com (Postfix) with ESMTPS id BFCFB19560AD; Mon, 1 Jul 2024 09:16:25 +0000 (UTC) Received: from fedora (unknown [10.72.112.45]) by mx-prod-int-02.mail-002.prod.us-west-2.aws.redhat.com (Postfix) with ESMTPS id 85E941956089; Mon, 1 Jul 2024 09:16:16 +0000 (UTC) Date: Mon, 1 Jul 2024 17:16:11 +0800 From: Ming Lei To: Hannes Reinecke Cc: Daniel Wagner , Jens Axboe , Keith Busch , Sagi Grimberg , Thomas Gleixner , Christoph Hellwig , Frederic Weisbecker , Mel Gorman , Sridhar Balaraman , "brookxu.cn" , linux-kernel@vger.kernel.org, linux-block@vger.kernel.org, linux-nvme@lists.infradead.org Subject: Re: [PATCH v2 3/3] lib/group_cpus.c: honor housekeeping config when grouping CPUs Message-ID: References: <20240627-isolcpus-io-queues-v2-0-26a32e3c4f75@suse.de> <20240627-isolcpus-io-queues-v2-3-26a32e3c4f75@suse.de> <0d8a5256-9719-45c5-b098-237b5a82fd36@suse.de> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <0d8a5256-9719-45c5-b098-237b5a82fd36@suse.de> X-Scanned-By: MIMEDefang 3.0 on 10.30.177.15 X-CRM114-Version: 20100106-BlameMichelson ( TRE 0.8.0 (BSD) ) MR-646709E3 X-CRM114-CacheID: sfid-20240701_021632_887994_89FD1AE8 X-CRM114-Status: GOOD ( 29.70 ) 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 Mon, Jul 01, 2024 at 10:43:14AM +0200, Hannes Reinecke wrote: > On 7/1/24 09:21, Ming Lei wrote: > > On Mon, Jul 01, 2024 at 09:08:32AM +0200, Daniel Wagner wrote: > > > On Sun, Jun 30, 2024 at 09:39:59PM GMT, Ming Lei wrote: > > > > > Make group_cpus_evenly aware of isolcpus configuration and use the > > > > > housekeeping CPU mask as base for distributing the available CPUs into > > > > > groups. > > > > > > > > > > Fixes: 11ea68f553e2 ("genirq, sched/isolation: Isolate from handling managed interrupts") > > > > > > > > isolated CPUs are actually handled when figuring out irq effective mask, > > > > so not sure how commit 11ea68f553e2 is wrong, and what is fixed in this > > > > patch from user viewpoint? > > > > > > IO queues are allocated/spread on the isolated CPUs and if there is an > > > thread submitting IOs from an isolated CPU it will cause noise on the > > > isolated CPUs. The question is this a use case you need/want to support? > > > > I have talked RH Openshift team weeks ago and they have such usage. > > > > userspace is free to run any application from isolated CPUs via 'taskset > > -c' even though 'isolcpus=' is passed from command line. > > > > Kernel can not add such new constraint on userspace. > > > > > We have customers who are complaining that even with isolcpus provided > > > they still see IO noise on the isolated CPUs. > > > > That is another issue, which has been fixed by the following patch: > > > > a46c27026da1 blk-mq: don't schedule block kworker on isolated CPUs > > > Hmm. Just when I thought I understood the issue ... > > How is this supposed to work, then, given that I/O can be initiated > from the isolated CPUs? > I would have accepted that we have two scheduling domains, blk-mq is > spread across all cpus, and the blk-mq cpusets are arranged according > to the isolcpu settings. > Then we can initiate I/O from the isolated cpus, and the scheduler > would 'magically' ensure that everything is only run on isolated cpus. blk-mq issues IO either from current context or kblockd context. > > But that patch would completely counteract such a setup, as during > I/O we more often than not will invoke kblockd, which then would cause > cross-talk on non-isolated cpus. If IO is submitted from isolated CPU, blk-mq will issue this IO via unbound kblockd WQ, which is guaranteed to not run on isolated CPUs. Thanks, Ming