From: Keith Busch <email@example.com> To: Ming Lei <firstname.lastname@example.org> Cc: Bart Van Assche <email@example.com>, Christoph Hellwig <firstname.lastname@example.org>, email@example.com, John Garry <firstname.lastname@example.org>, Hannes Reinecke <email@example.com>, Thomas Gleixner <firstname.lastname@example.org> Subject: Re: blk-mq: improvement CPU hotplug (simplified version) v3 Date: Fri, 22 May 2020 07:47:20 -0700 Message-ID: <20200522144720.GC3423299@dhcp-10-100-145-180.wdl.wdc.com> (raw) In-Reply-To: <20200522023923.GC755458@T590> On Fri, May 22, 2020 at 10:39:23AM +0800, Ming Lei wrote: > On Thu, May 21, 2020 at 12:15:52PM -0700, Bart Van Assche wrote: > > On 2020-05-20 21:33, Ming Lei wrote: > > > No. > > > > > > If vector 3 is for covering hw queue 12 ~ 15, the vector shouldn't be > > > shutdown when cpu 14 is offline. > > >> Also I am pretty sure that we don't do this way with managed IRQ. And > > > non-managed IRQ will be migrated to other online cpus during cpu offline, > > > so not an issue at all. See migrate_one_irq(). > > > > Thanks for the pointer to migrate_one_irq(). > > > > However, I'm not convinced the above statement is correct. My > > understanding is that the block driver knows which interrupt vector has > > been associated with which hardware queue but the blk-mq core not. It > > seems to me that patch 6/6 of this series is based on the following > > assumptions: > > (a) That the interrupt that is associated with a hardware queue is > > processed by one of the CPU's in hctx->cpumask. > > (b) That hardware queues do not share interrupt vectors. > > > > I don't think that either assumption is correct. > > What the patch tries to do is just: > > - when the last cpu of hctx->cpumask is going to become offline, mark > this hctx as inactive, then drain any inflight IO requests originated > from this hctx > > The correctness is that once we stops to produce request, we can drain > any in-flight requests before shutdown the last cpu of hctx. Then finally > this hctx becomes quiesced completely. Do you think this way is wrong? > If yes, please prove it. I don't think this applies to what Bart is saying, but there is a pathological case where things break down: if a driver uses managed irq's, but doesn't use the same affinity for the hctx's, an offline cpu may have been the only one providing irq handling for an online hctx. I feel like that should be a driver bug if it were to set itself up that way, but I don't find anything enforces that.
next prev parent reply index Thread overview: 31+ messages / expand[flat|nested] mbox.gz Atom feed top 2020-05-20 17:06 Christoph Hellwig 2020-05-20 17:06 ` [PATCH 1/6] blk-mq: remove the bio argument to ->prepare_request Christoph Hellwig 2020-05-20 18:16 ` Bart Van Assche 2020-05-22 9:11 ` Hannes Reinecke 2020-05-20 17:06 ` [PATCH 2/6] blk-mq: simplify the blk_mq_get_request calling convention Christoph Hellwig 2020-05-20 18:22 ` Bart Van Assche 2020-05-22 9:13 ` Hannes Reinecke 2020-05-20 17:06 ` [PATCH 3/6] blk-mq: move more request initialization to blk_mq_rq_ctx_init Christoph Hellwig 2020-05-20 20:10 ` Bart Van Assche 2020-05-20 17:06 ` [PATCH 4/6] blk-mq: open code __blk_mq_alloc_request in blk_mq_alloc_request_hctx Christoph Hellwig 2020-05-22 9:17 ` Hannes Reinecke 2020-05-20 17:06 ` [PATCH 5/6] blk-mq: add blk_mq_all_tag_iter Christoph Hellwig 2020-05-20 20:24 ` Bart Van Assche 2020-05-27 6:05 ` Christoph Hellwig 2020-05-22 9:18 ` Hannes Reinecke 2020-05-20 17:06 ` [PATCH 6/6] blk-mq: drain I/O when all CPUs in a hctx are offline Christoph Hellwig 2020-05-22 9:25 ` Hannes Reinecke 2020-05-25 9:20 ` Ming Lei 2020-05-20 21:46 ` blk-mq: improvement CPU hotplug (simplified version) v3 Bart Van Assche 2020-05-21 2:57 ` Ming Lei 2020-05-21 3:50 ` Bart Van Assche 2020-05-21 4:33 ` Ming Lei 2020-05-21 19:15 ` Bart Van Assche 2020-05-22 2:39 ` Ming Lei 2020-05-22 14:47 ` Keith Busch [this message] 2020-05-23 3:05 ` Ming Lei 2020-05-23 15:19 ` Bart Van Assche 2020-05-25 4:09 ` Ming Lei 2020-05-25 15:32 ` Bart Van Assche 2020-05-25 16:38 ` Keith Busch 2020-05-26 0:37 ` Ming Lei
Reply instructions: You may reply publicly to this message via plain-text email using any one of the following methods: * Save the following mbox file, import it into your mail client, and reply-to-all from there: mbox Avoid top-posting and favor interleaved quoting: https://en.wikipedia.org/wiki/Posting_style#Interleaved_style * Reply using the --to, --cc, and --in-reply-to switches of git-send-email(1): git send-email \ --in-reply-to=20200522144720.GC3423299@dhcp-10-100-145-180.wdl.wdc.com \ --email@example.com \ --firstname.lastname@example.org \ --email@example.com \ --firstname.lastname@example.org \ --email@example.com \ --firstname.lastname@example.org \ --email@example.com \ --firstname.lastname@example.org \ /path/to/YOUR_REPLY https://kernel.org/pub/software/scm/git/docs/git-send-email.html * If your mail client supports setting the In-Reply-To header via mailto: links, try the mailto: link
Linux-Block Archive on lore.kernel.org Archives are clonable: git clone --mirror https://lore.kernel.org/linux-block/0 linux-block/git/0.git # If you have public-inbox 1.1+ installed, you may # initialize and index your mirror using the following commands: public-inbox-init -V2 linux-block linux-block/ https://lore.kernel.org/linux-block \ email@example.com public-inbox-index linux-block Example config snippet for mirrors Newsgroup available over NNTP: nntp://nntp.lore.kernel.org/org.kernel.vger.linux-block AGPL code for this site: git clone https://public-inbox.org/public-inbox.git