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Thu, 19 Dec 2024 15:38:44 +0000 (UTC) Received: from dovecot-director2.suse.de ([2a07:de40:b281:106:10:150:64:167]) by imap1.dmz-prg2.suse.org with ESMTPSA id bzRPAwQ+ZGc2PgAAD6G6ig (envelope-from ); Thu, 19 Dec 2024 15:38:44 +0000 Date: Thu, 19 Dec 2024 16:38:43 +0100 From: Daniel Wagner To: Ming Lei Cc: Daniel Wagner , Jens Axboe , Keith Busch , Christoph Hellwig , Sagi Grimberg , Kashyap Desai , Sumit Saxena , Shivasharan S , Chandrakanth patil , "Martin K. Petersen" , Nilesh Javali , GR-QLogic-Storage-Upstream@marvell.com, Don Brace , "Michael S. Tsirkin" , Jason Wang , Paolo Bonzini , Stefan Hajnoczi , Eugenio =?utf-8?B?UMOpcmV6?= , Xuan Zhuo , Andrew Morton , Thomas Gleixner , Costa Shulyupin , Juri Lelli , Valentin Schneider , Waiman Long , Michal =?utf-8?Q?Koutn=C3=BD?= , Frederic Weisbecker , Mel Gorman , Hannes Reinecke , Sridhar Balaraman , "brookxu.cn" , linux-kernel@vger.kernel.org, linux-block@vger.kernel.org, linux-nvme@lists.infradead.org, megaraidlinux.pdl@broadcom.com, linux-scsi@vger.kernel.org, storagedev@microchip.com, virtualization@lists.linux.dev Subject: Re: [PATCH v4 8/9] blk-mq: use hk cpus only when isolcpus=managed_irq is enabled Message-ID: References: <20241217-isolcpus-io-queues-v4-0-5d355fbb1e14@kernel.org> <20241217-isolcpus-io-queues-v4-8-5d355fbb1e14@kernel.org> Precedence: bulk X-Mailing-List: virtualization@lists.linux.dev List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: X-Rspamd-Queue-Id: 2DC081F392 X-Spam-Score: -3.01 X-Rspamd-Action: no action X-Spamd-Result: default: False [-3.01 / 50.00]; BAYES_HAM(-3.00)[99.99%]; SUSPICIOUS_RECIPS(1.50)[]; NEURAL_HAM_LONG(-1.00)[-1.000]; R_DKIM_ALLOW(-0.20)[suse.de:s=susede2_rsa,suse.de:s=susede2_ed25519]; NEURAL_HAM_SHORT(-0.20)[-1.000]; MIME_GOOD(-0.10)[text/plain]; MX_GOOD(-0.01)[]; TO_MATCH_ENVRCPT_ALL(0.00)[]; FREEMAIL_ENVRCPT(0.00)[gmail.com]; DKIM_SIGNED(0.00)[suse.de:s=susede2_rsa,suse.de:s=susede2_ed25519]; ARC_NA(0.00)[]; FUZZY_BLOCKED(0.00)[rspamd.com]; RCPT_COUNT_TWELVE(0.00)[39]; MIME_TRACE(0.00)[0:+]; FREEMAIL_CC(0.00)[kernel.org,kernel.dk,lst.de,grimberg.me,broadcom.com,oracle.com,marvell.com,microchip.com,redhat.com,linux.alibaba.com,linux-foundation.org,linutronix.de,suse.com,suse.de,parallelwireless.com,gmail.com,vger.kernel.org,lists.infradead.org,lists.linux.dev]; RCVD_TLS_ALL(0.00)[]; DKIM_TRACE(0.00)[suse.de:+]; RCVD_COUNT_TWO(0.00)[2]; FROM_EQ_ENVFROM(0.00)[]; FROM_HAS_DN(0.00)[]; TO_DN_SOME(0.00)[]; TAGGED_RCPT(0.00)[]; ASN(0.00)[asn:25478, ipnet:::/0, country:RU]; RCVD_VIA_SMTP_AUTH(0.00)[]; R_RATELIMIT(0.00)[to_ip_from(RLy1uc785cwzda5mnrw36e8hj5)]; MISSING_XM_UA(0.00)[]; DBL_BLOCKED_OPENRESOLVER(0.00)[suse.de:dkim,imap1.dmz-prg2.suse.org:rdns,imap1.dmz-prg2.suse.org:helo] X-Rspamd-Server: rspamd1.dmz-prg2.suse.org X-Spam-Flag: NO X-Spam-Level: On Thu, Dec 19, 2024 at 05:20:44PM +0800, Ming Lei wrote: > > + cpumask_andnot(isol_mask, > > + cpu_possible_mask, > > + housekeeping_cpumask(HK_TYPE_MANAGED_IRQ)); > > + > > + for_each_cpu(cpu, isol_mask) { > > + qmap->mq_map[cpu] = qmap->queue_offset + queue; > > + queue = (queue + 1) % qmap->nr_queues; > > + } > > Looks the IO hang issue in V3 isn't addressed yet, is it? > > https://lore.kernel.org/linux-block/ZrtX4pzqwVUEgIPS@fedora/ I've added an explanation in the cover letter why this is not addressed. From the cover letter: I've experimented for a while and all solutions I came up were horrible hacks (the hotpath needs to be touched) and I don't want to slow down all other users (which are almost everyone). IMO, it's just not worth trying to fix this corner case. If the user is using isolcpus and does CPU hotplug, we can expect that the user can also first offline the isolated CPUs. I've discussed this topic during ALPSS and the room came to the same conclusion. Thus I just added a patch which issues a warning that IOs are likely to hang.