From patchwork Fri Dec 4 19:13:56 2020 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Sebastian Andrzej Siewior X-Patchwork-Id: 11952179 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-15.8 required=3.0 tests=BAYES_00,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_CR_TRAILER, INCLUDES_PATCH,MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS,URIBL_BLOCKED autolearn=ham autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 54F3EC4167B for ; Fri, 4 Dec 2020 19:14:53 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 019E822CAE for ; Fri, 4 Dec 2020 19:14:52 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1727199AbgLDTOw (ORCPT ); Fri, 4 Dec 2020 14:14:52 -0500 Received: from Galois.linutronix.de ([193.142.43.55]:49392 "EHLO galois.linutronix.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1728079AbgLDTOs (ORCPT ); Fri, 4 Dec 2020 14:14:48 -0500 From: Sebastian Andrzej Siewior DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=linutronix.de; s=2020; t=1607109245; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references; bh=sBZVA+aUErTEHExNncbFL8kYuUQMpfZGtQo4vtsCy2c=; b=HBCiux5IzSNRxBSR/n3Sinu760jNxDTg9mB1HEgzPCIjKRvrmGEDX0jL7cYQCdprY2/Tr1 QvWh8CBYIc+l3p3Dp4Q5uqUcLZNf2DJQAbvOl7vU9zYOHg9XaUYiwV3Ki7B2eNB2ebYtM0 sn3SJdU2cbGgvkVCUWA2M89qb6ClD/Iw5GS15E83oqkkHg3VsFQYWt6tN0mM5UjlpwGgoW Aaw9+wpDWryHfPnn0zfVlPWpjXAF+qE1uwyF53t0gbymcHxpkiDzJXwgvgQ5T1LXnrr6gb JgE/m/iRUAHbHi/RGqLqyqjEvrmsTAhN9o0H0hpYqxfGqLtRY8+F5i/M7X1t7A== DKIM-Signature: v=1; a=ed25519-sha256; c=relaxed/relaxed; d=linutronix.de; s=2020e; t=1607109245; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references; bh=sBZVA+aUErTEHExNncbFL8kYuUQMpfZGtQo4vtsCy2c=; b=GOwMbCjVDKMonuC3piKobx2KCG9xwLAf9Q78PU/WxZvz5+x0fdtW70gzNBvgm3FJANwqW5 tZdgo64j0qUIvMDQ== To: linux-block@vger.kernel.org Cc: Jens Axboe , Thomas Gleixner , Peter Zijlstra , Daniel Wagner , Mike Galbraith , Christoph Hellwig , Sagi Grimberg , Sebastian Andrzej Siewior Subject: [PATCH 3/3] blk-mq: Use llist_head for blk_cpu_done Date: Fri, 4 Dec 2020 20:13:56 +0100 Message-Id: <20201204191356.2516405-4-bigeasy@linutronix.de> In-Reply-To: <20201204191356.2516405-1-bigeasy@linutronix.de> References: <20201204191356.2516405-1-bigeasy@linutronix.de> MIME-Version: 1.0 Precedence: bulk List-ID: X-Mailing-List: linux-block@vger.kernel.org With llist_head it is possible to avoid the locking (the irq-off region) when items are added. This makes it possible to add items on a remote CPU. llist_add() returns true if the list was previously empty. This can be used to invoke the SMP function call / raise sofirq only if the first item was added (otherwise it is already pending). This simplifies the code a little and reduces the IRQ-off regions. With this change it possible to reduce the SMP-function call a simple __raise_softirq_irqoff(). blk_mq_complete_request_remote() needs a preempt-disable section if the request needs to complete on the local CPU. Some callers (USB-storage) invoke this preemptible context and the request needs to be enqueued on the same CPU as the softirq is raised. Signed-off-by: Sebastian Andrzej Siewior --- block/blk-mq.c | 77 ++++++++++++++---------------------------- include/linux/blkdev.h | 2 +- 2 files changed, 27 insertions(+), 52 deletions(-) diff --git a/block/blk-mq.c b/block/blk-mq.c index 3c0e94913d874..b5138327952a4 100644 --- a/block/blk-mq.c +++ b/block/blk-mq.c @@ -41,7 +41,7 @@ #include "blk-mq-sched.h" #include "blk-rq-qos.h" -static DEFINE_PER_CPU(struct list_head, blk_cpu_done); +static DEFINE_PER_CPU(struct llist_head, blk_cpu_done); static void blk_mq_poll_stats_start(struct request_queue *q); static void blk_mq_poll_stats_fn(struct blk_stat_callback *cb); @@ -567,68 +567,32 @@ void blk_mq_end_request(struct request *rq, blk_status_t error) } EXPORT_SYMBOL(blk_mq_end_request); -/* - * Softirq action handler - move entries to local list and loop over them - * while passing them to the queue registered handler. - */ -static __latent_entropy void blk_done_softirq(struct softirq_action *h) +static void blk_complete_reqs(struct llist_head *cpu_list) { - struct list_head *cpu_list, local_list; + struct llist_node *entry; + struct request *rq, *rq_next; - local_irq_disable(); - cpu_list = this_cpu_ptr(&blk_cpu_done); - list_replace_init(cpu_list, &local_list); - local_irq_enable(); + entry = llist_del_all(cpu_list); + entry = llist_reverse_order(entry); - while (!list_empty(&local_list)) { - struct request *rq; - - rq = list_entry(local_list.next, struct request, ipi_list); - list_del_init(&rq->ipi_list); + llist_for_each_entry_safe(rq, rq_next, entry, ipi_list) rq->q->mq_ops->complete(rq); - } } -static void blk_mq_trigger_softirq(struct request *rq) +static __latent_entropy void blk_done_softirq(struct softirq_action *h) { - struct list_head *list; - unsigned long flags; - - local_irq_save(flags); - list = this_cpu_ptr(&blk_cpu_done); - list_add_tail(&rq->ipi_list, list); - - /* - * If the list only contains our just added request, signal a raise of - * the softirq. If there are already entries there, someone already - * raised the irq but it hasn't run yet. - */ - if (list->next == &rq->ipi_list) - raise_softirq_irqoff(BLOCK_SOFTIRQ); - local_irq_restore(flags); + blk_complete_reqs(this_cpu_ptr(&blk_cpu_done)); } static int blk_softirq_cpu_dead(unsigned int cpu) { - /* - * If a CPU goes away, splice its entries to the current CPU - * and trigger a run of the softirq - */ - local_irq_disable(); - list_splice_init(&per_cpu(blk_cpu_done, cpu), - this_cpu_ptr(&blk_cpu_done)); - raise_softirq_irqoff(BLOCK_SOFTIRQ); - local_irq_enable(); - + blk_complete_reqs(&per_cpu(blk_cpu_done, cpu)); return 0; } - static void __blk_mq_complete_request_remote(void *data) { - struct request *rq = data; - - blk_mq_trigger_softirq(rq); + __raise_softirq_irqoff(BLOCK_SOFTIRQ); } static inline bool blk_mq_complete_need_ipi(struct request *rq) @@ -659,6 +623,7 @@ static inline bool blk_mq_complete_need_ipi(struct request *rq) bool blk_mq_complete_request_remote(struct request *rq) { + struct llist_head *cpu_list; WRITE_ONCE(rq->state, MQ_RQ_COMPLETE); /* @@ -669,12 +634,22 @@ bool blk_mq_complete_request_remote(struct request *rq) return false; if (blk_mq_complete_need_ipi(rq)) { - INIT_CSD(&rq->csd, __blk_mq_complete_request_remote, rq); - smp_call_function_single_async(rq->mq_ctx->cpu, &rq->csd); + unsigned int cpu; + + cpu = rq->mq_ctx->cpu; + cpu_list = &per_cpu(blk_cpu_done, cpu); + if (llist_add(&rq->ipi_list, cpu_list)) { + INIT_CSD(&rq->csd, __blk_mq_complete_request_remote, rq); + smp_call_function_single_async(cpu, &rq->csd); + } } else { if (rq->q->nr_hw_queues > 1) return false; - blk_mq_trigger_softirq(rq); + preempt_disable(); + cpu_list = this_cpu_ptr(&blk_cpu_done); + if (llist_add(&rq->ipi_list, cpu_list)) + raise_softirq(BLOCK_SOFTIRQ); + preempt_enable(); } return true; @@ -3905,7 +3880,7 @@ static int __init blk_mq_init(void) int i; for_each_possible_cpu(i) - INIT_LIST_HEAD(&per_cpu(blk_cpu_done, i)); + init_llist_head(&per_cpu(blk_cpu_done, i)); open_softirq(BLOCK_SOFTIRQ, blk_done_softirq); cpuhp_setup_state_nocalls(CPUHP_BLOCK_SOFTIRQ_DEAD, diff --git a/include/linux/blkdev.h b/include/linux/blkdev.h index 17cedf0dc83db..7b05390766eec 100644 --- a/include/linux/blkdev.h +++ b/include/linux/blkdev.h @@ -156,7 +156,7 @@ struct request { */ union { struct hlist_node hash; /* merge hash */ - struct list_head ipi_list; + struct llist_node ipi_list; }; /*