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Subject[RFC PATCH 3/3] blk-mq: complete request in rescuer process context in case of irq flood
Date
When irq flood is detected, complete requests in the percpu rescuer
context for avoiding lockup cpu.

IO interrupt flood might be triggered in the following situations:

1) the storage device is quicker to handle IO than single CPU core

2) N:1 queue mapping, single CPU core is saturated by handling IO interrupts
from multiple storage disks or multiple HBAs

Cc: Long Li <longli@microsoft.com>
Cc: Ingo Molnar <mingo@redhat.com>,
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Keith Busch <keith.busch@intel.com>
Cc: Christoph Hellwig <hch@lst.de>
Cc: Sagi Grimberg <sagi@grimberg.me>
Cc: John Garry <john.garry@huawei.com>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Hannes Reinecke <hare@suse.com>
Signed-off-by: Ming Lei <ming.lei@redhat.com>
---
block/blk-mq.c | 68 +++++++++++++++++++++++++++++++++++++++++++++++++-
1 file changed, 67 insertions(+), 1 deletion(-)

diff --git a/block/blk-mq.c b/block/blk-mq.c
index 323c9cb28066..a7fe00f1a313 100644
--- a/block/blk-mq.c
+++ b/block/blk-mq.c
@@ -40,6 +40,14 @@
#include "blk-mq-sched.h"
#include "blk-rq-qos.h"

+struct blk_mq_comp_rescuer {
+ struct list_head head;
+ bool running;
+ struct work_struct work;
+};
+
+static DEFINE_PER_CPU(struct blk_mq_comp_rescuer, blk_mq_comp_rescuer);
+
static void blk_mq_poll_stats_start(struct request_queue *q);
static void blk_mq_poll_stats_fn(struct blk_stat_callback *cb);

@@ -624,6 +632,50 @@ static void hctx_lock(struct blk_mq_hw_ctx *hctx, int *srcu_idx)
*srcu_idx = srcu_read_lock(hctx->srcu);
}

+static void blk_mq_complete_rq_in_rescuer(struct request *rq)
+{
+ struct blk_mq_comp_rescuer *rescuer;
+ unsigned long flags;
+
+ WARN_ON(!in_interrupt());
+
+ local_irq_save(flags);
+ rescuer = this_cpu_ptr(&blk_mq_comp_rescuer);
+ list_add_tail(&rq->queuelist, &rescuer->head);
+ if (!rescuer->running) {
+ rescuer->running = true;
+ kblockd_schedule_work(&rescuer->work);
+ }
+ local_irq_restore(flags);
+
+}
+
+static void blk_mq_complete_rescue_work(struct work_struct *work)
+{
+ struct blk_mq_comp_rescuer *rescuer =
+ container_of(work, struct blk_mq_comp_rescuer, work);
+ struct list_head local_list;
+
+ local_irq_disable();
+ run_again:
+ list_replace_init(&rescuer->head, &local_list);
+ local_irq_enable();
+
+ while (!list_empty(&local_list)) {
+ struct request *rq = list_entry(local_list.next,
+ struct request, queuelist);
+ list_del_init(&rq->queuelist);
+ __blk_mq_complete_request(rq);
+ cond_resched();
+ }
+
+ local_irq_disable();
+ if (!list_empty(&rescuer->head))
+ goto run_again;
+ rescuer->running = false;
+ local_irq_enable();
+}
+
/**
* blk_mq_complete_request - end I/O on a request
* @rq: the request being processed
@@ -636,7 +688,11 @@ bool blk_mq_complete_request(struct request *rq)
{
if (unlikely(blk_should_fake_timeout(rq->q)))
return false;
- __blk_mq_complete_request(rq);
+
+ if (likely(!irq_is_flood() || !in_interrupt()))
+ __blk_mq_complete_request(rq);
+ else
+ blk_mq_complete_rq_in_rescuer(rq);
return true;
}
EXPORT_SYMBOL(blk_mq_complete_request);
@@ -3525,6 +3581,16 @@ EXPORT_SYMBOL(blk_mq_rq_cpu);

static int __init blk_mq_init(void)
{
+ int i;
+
+ for_each_possible_cpu(i) {
+ struct blk_mq_comp_rescuer *rescuer =
+ &per_cpu(blk_mq_comp_rescuer, i);
+
+ INIT_LIST_HEAD(&rescuer->head);
+ INIT_WORK(&rescuer->work, blk_mq_complete_rescue_work);
+ }
+
cpuhp_setup_state_multi(CPUHP_BLK_MQ_DEAD, "block/mq:dead", NULL,
blk_mq_hctx_notify_dead);
return 0;
--
2.20.1
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