linux-kernel.vger.kernel.org archive mirror
 help / color / mirror / Atom feed
From: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
To: linux-block@vger.kernel.org
Cc: Christoph Hellwig <hch@infradead.org>,
	Thomas Gleixner <tglx@linutronix.de>,
	David Runge <dave@sleepmap.de>,
	linux-rt-users@vger.kernel.org, Jens Axboe <axboe@kernel.dk>,
	linux-kernel@vger.kernel.org,
	Peter Zijlstra <peterz@infradead.org>,
	Daniel Wagner <dwagner@suse.de>,
	Sebastian Andrzej Siewior <bigeasy@linutronix.de>
Subject: [PATCH 3/3] blk-mq: Use llist_head for blk_cpu_done
Date: Wed, 28 Oct 2020 15:12:51 +0100	[thread overview]
Message-ID: <20201028141251.3608598-3-bigeasy@linutronix.de> (raw)
In-Reply-To: <20201028141251.3608598-1-bigeasy@linutronix.de>

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().

Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
---
 block/blk-mq.c         | 78 ++++++++++++++----------------------------
 include/linux/blkdev.h |  2 +-
 2 files changed, 26 insertions(+), 54 deletions(-)

diff --git a/block/blk-mq.c b/block/blk-mq.c
index 769d2d532a825..4f53de48e5038 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);
@@ -565,68 +565,32 @@ 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)
@@ -657,6 +621,7 @@ 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);
 
 	/*
@@ -667,14 +632,21 @@ bool blk_mq_complete_request_remote(struct request *rq)
 		return false;
 
 	if (blk_mq_complete_need_ipi(rq)) {
-		rq->csd.func = __blk_mq_complete_request_remote;
-		rq->csd.info = rq;
-		rq->csd.flags = 0;
-		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)) {
+			rq->csd.func = __blk_mq_complete_request_remote;
+			rq->csd.flags = 0;
+			smp_call_function_single_async(cpu, &rq->csd);
+		}
 	} else {
 		if (rq->q->nr_hw_queues > 1)
 			return false;
-		blk_mq_trigger_softirq(rq);
+		cpu_list = this_cpu_ptr(&blk_cpu_done);
+		if (llist_add(&rq->ipi_list, cpu_list))
+			raise_softirq(BLOCK_SOFTIRQ);
 	}
 
 	return true;
@@ -3905,7 +3877,7 @@ 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 639cae2c158b5..331b2b675b417 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;
 	};
 
 	/*
-- 
2.28.0


  parent reply	other threads:[~2020-10-28 22:30 UTC|newest]

Thread overview: 36+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
     [not found] <20201021175059.GA4989@hmbx>
2020-10-23 11:04 ` [PATCH RFC] blk-mq: Don't IPI requests on PREEMPT_RT Sebastian Andrzej Siewior
2020-10-23 11:21   ` Christoph Hellwig
2020-10-23 13:52     ` Sebastian Andrzej Siewior
2020-10-27  9:26       ` Christoph Hellwig
2020-10-27 10:11         ` Sebastian Andrzej Siewior
2020-10-27 16:07           ` Christoph Hellwig
2020-10-27 17:05             ` Thomas Gleixner
2020-10-27 17:23               ` Christoph Hellwig
2020-10-27 17:59                 ` Sebastian Andrzej Siewior
2020-10-27 20:58                 ` Sebastian Andrzej Siewior
2020-10-28  6:56                   ` Christoph Hellwig
2020-10-28 14:12                     ` [PATCH 1/3] blk-mq: Don't complete on a remote CPU in force threaded mode Sebastian Andrzej Siewior
2020-10-28 14:12                       ` [PATCH 2/3] blk-mq: Always complete remote completions requests in softirq Sebastian Andrzej Siewior
2020-10-28 14:12                       ` Sebastian Andrzej Siewior [this message]
2020-10-28 14:44                         ` [PATCH 3/3] blk-mq: Use llist_head for blk_cpu_done Christoph Hellwig
2020-10-28 14:47                           ` Sebastian Andrzej Siewior
2020-10-29 13:12                         ` Sebastian Andrzej Siewior
2020-10-29 14:05                           ` Christoph Hellwig
2020-10-29 14:56                             ` Sebastian Andrzej Siewior
2020-10-29 14:57                               ` Christoph Hellwig
2020-10-29 20:03                                 ` Sagi Grimberg
2020-10-29 21:01                                   ` Sebastian Andrzej Siewior
2020-10-29 21:07                                     ` Sagi Grimberg
2020-10-31 10:41                                       ` Sebastian Andrzej Siewior
2020-10-31 15:00                                         ` Jens Axboe
2020-10-31 15:01                                           ` Jens Axboe
2020-10-31 18:09                                             ` Christoph Hellwig
2020-11-02  9:55                                           ` Sebastian Andrzej Siewior
2020-11-02 18:12                                             ` Christoph Hellwig
2020-11-04 19:15                                               ` Sagi Grimberg
2020-11-06 15:23                                               ` Sebastian Andrzej Siewior
2020-10-28 10:04                 ` [PATCH RFC] blk-mq: Don't IPI requests on PREEMPT_RT Peter Zijlstra
2021-01-23 20:10 [PATCH v3 0/3] blk-mq: Don't complete in IRQ, use llist_head Sebastian Andrzej Siewior
2021-01-23 20:10 ` [PATCH 3/3] blk-mq: Use llist_head for blk_cpu_done Sebastian Andrzej Siewior
2021-01-25  8:30   ` Christoph Hellwig
2021-01-25  8:32     ` Sebastian Andrzej Siewior
2021-01-25  8:39       ` Christoph Hellwig

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=20201028141251.3608598-3-bigeasy@linutronix.de \
    --to=bigeasy@linutronix.de \
    --cc=axboe@kernel.dk \
    --cc=dave@sleepmap.de \
    --cc=dwagner@suse.de \
    --cc=hch@infradead.org \
    --cc=linux-block@vger.kernel.org \
    --cc=linux-kernel@vger.kernel.org \
    --cc=linux-rt-users@vger.kernel.org \
    --cc=peterz@infradead.org \
    --cc=tglx@linutronix.de \
    /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
Be sure your reply has a Subject: header at the top and a blank line before the message body.
This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox;
as well as URLs for NNTP newsgroup(s).