From patchwork Mon Jan 25 09:54:12 2021 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 8bit X-Patchwork-Submitter: Sebastian Andrzej Siewior X-Patchwork-Id: 12043125 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 CF3E5C433E0 for ; Mon, 25 Jan 2021 09:58:02 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 74DBC225AB for ; Mon, 25 Jan 2021 09:58:02 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1727235AbhAYJ5F (ORCPT ); Mon, 25 Jan 2021 04:57:05 -0500 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:41892 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1727061AbhAYJ4l (ORCPT ); Mon, 25 Jan 2021 04:56:41 -0500 Received: from galois.linutronix.de (Galois.linutronix.de [IPv6:2a0a:51c0:0:12e:550::1]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 420B4C061794; Mon, 25 Jan 2021 01:54:14 -0800 (PST) Date: Mon, 25 Jan 2021 10:54:12 +0100 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=linutronix.de; s=2020; t=1611568452; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version:content-type:content-type: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references; bh=En+PvuTxJbTaSF56ABQ0NQAdfK6Gng9dHg0giYYwJFE=; b=GxGMLNJTLzBSohgS50rUkkbgTtdwGe2Xj/9xt8GaGsC/JvYFcuJmujjXDfell0RwilfUDr kOzJw/mDywtTh9BchdlnjsoTEFlfRbn3YvlgSoE8rB3uoWnMZ5G5QLKpBjn18QRtOG3zVU 4hTIwAC9Ia5cj8xCaBYwiMn6+hDtqWm5ajNKPF5rGsSXrL02T2GA6l1JX2AZP6LfdWcl9R qJLmm8aYF+2sjkzNNMmxNTeZ87+RAe/Y6hk3UeBjnJe/QiZMMZVv7FUlxwb4sI5pdMjuvX yaqUk0qs6va7vuRCE1OAyB1H65VRzrxbw0rUH7X2yLX2HbBQvVJZ5AQN3y8tiA== DKIM-Signature: v=1; a=ed25519-sha256; c=relaxed/relaxed; d=linutronix.de; s=2020e; t=1611568452; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version:content-type:content-type: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references; bh=En+PvuTxJbTaSF56ABQ0NQAdfK6Gng9dHg0giYYwJFE=; b=tx0I+MKzUAKZuVs+7/M38+6CjW1DLBOtMFDSMheUlFHRVANB4J7DGg951SE5ApmebeYl5U OUIC9rzyEi7QTVBw== From: Sebastian Andrzej Siewior To: Christoph Hellwig Cc: linux-block@vger.kernel.org, linux-kernel@vger.kernel.org, Jens Axboe , Thomas Gleixner , Peter Zijlstra , Ingo Molnar Subject: [PATCH 3/3 v2] blk-mq: Use llist_head for blk_cpu_done Message-ID: <20210125095412.qxknd2vbsmgtrhqb@linutronix.de> References: <20210123201027.3262800-1-bigeasy@linutronix.de> <20210123201027.3262800-4-bigeasy@linutronix.de> <20210125083012.GD942655@infradead.org> <20210125083204.ahddujk5m6njwbju@linutronix.de> <20210125083903.GB945284@infradead.org> MIME-Version: 1.0 Content-Disposition: inline In-Reply-To: <20210125083903.GB945284@infradead.org> 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 without additional locking. 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. blk_mq_raise_softirq() needs a preempt-disable section to ensure the request is enqueued on the same CPU as the softirq is raised. Some callers (USB-storage) invoke this path in preemptible context. Signed-off-by: Sebastian Andrzej Siewior Reviewed-by: Christoph Hellwig Reviewed-by: Daniel Wagner --- v1…v2: Move var initialisation to declaration in blk_mq_complete_send_ipi(). Suggested by hch. block/blk-mq.c | 95 +++++++++++++++++------------------------- include/linux/blkdev.h | 2 +- 2 files changed, 40 insertions(+), 57 deletions(-) diff --git a/block/blk-mq.c b/block/blk-mq.c index 90348ae518461..8429be0d9b8dd 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 +567,29 @@ 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 *list) { - struct list_head *cpu_list, local_list; + struct llist_node *entry = llist_reverse_order(llist_del_all(list)); + struct request *rq, *next; - local_irq_disable(); - cpu_list = this_cpu_ptr(&blk_cpu_done); - list_replace_init(cpu_list, &local_list); - local_irq_enable(); - - 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, 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) @@ -657,6 +618,28 @@ static inline bool blk_mq_complete_need_ipi(struct request *rq) return cpu_online(rq->mq_ctx->cpu); } +static void blk_mq_complete_send_ipi(struct request *rq) +{ + unsigned int cpu = rq->mq_ctx->cpu; + struct llist_head *list = &per_cpu(blk_cpu_done, cpu); + + if (llist_add(&rq->ipi_list, list)) { + INIT_CSD(&rq->csd, __blk_mq_complete_request_remote, rq); + smp_call_function_single_async(cpu, &rq->csd); + } +} + +static void blk_mq_raise_softirq(struct request *rq) +{ + struct llist_head *list; + + preempt_disable(); + list = this_cpu_ptr(&blk_cpu_done); + if (llist_add(&rq->ipi_list, list)) + raise_softirq(BLOCK_SOFTIRQ); + preempt_enable(); +} + bool blk_mq_complete_request_remote(struct request *rq) { WRITE_ONCE(rq->state, MQ_RQ_COMPLETE); @@ -669,15 +652,15 @@ 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); - } else { - if (rq->q->nr_hw_queues > 1) - return false; - blk_mq_trigger_softirq(rq); + blk_mq_complete_send_ipi(rq); + return true; } - return true; + if (rq->q->nr_hw_queues == 1) { + blk_mq_raise_softirq(rq); + return true; + } + return false; } EXPORT_SYMBOL_GPL(blk_mq_complete_request_remote); @@ -3892,7 +3875,7 @@ 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 f94ee3089e015..89a444c5a5833 100644 --- a/include/linux/blkdev.h +++ b/include/linux/blkdev.h @@ -153,7 +153,7 @@ struct request { */ union { struct hlist_node hash; /* merge hash */ - struct list_head ipi_list; + struct llist_node ipi_list; }; /*