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
next prev 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
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