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Subject[PATCH 1/2] blk_mq: call preempt_disable/enable in blk_mq_run_hw_queue, and only if needed
Date
preempt_disable/enable surrounds every call to blk_mq_run_hw_queue,
except the one in blk-flush.c. In fact that one is always asynchronous,
and it does not need smp_processor_id().

We can do the same for all other calls, avoiding preempt_disable when
async is true. This avoids peppering blk-mq.c with preemption-disabled
regions.

Cc: Jens Axboe <axboe@kernel.dk>
Cc: Thomas Gleixner <tglx@linutronix.de>
Reported-by: Clark Williams <williams@redhat.com>
Tested-by: Clark Williams <williams@redhat.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
---
block/blk-mq.c | 21 ++++++++++++---------
1 file changed, 12 insertions(+), 9 deletions(-)

diff --git a/block/blk-mq.c b/block/blk-mq.c
index df8e1e09dd17..c6192ba78950 100644
--- a/block/blk-mq.c
+++ b/block/blk-mq.c
@@ -828,9 +828,18 @@ void blk_mq_run_hw_queue(struct blk_mq_hw_ctx *hctx, bool async)
if (unlikely(test_bit(BLK_MQ_S_STOPPED, &hctx->state)))
return;

- if (!async && cpumask_test_cpu(smp_processor_id(), hctx->cpumask))
- __blk_mq_run_hw_queue(hctx);
- else if (hctx->queue->nr_hw_queues == 1)
+ if (!async) {
+ preempt_disable();
+ if (cpumask_test_cpu(smp_processor_id(), hctx->cpumask)) {
+ __blk_mq_run_hw_queue(hctx);
+ preempt_enable();
+ return;
+ }
+
+ preempt_enable();
+ }
+
+ if (hctx->queue->nr_hw_queues == 1)
kblockd_schedule_delayed_work(&hctx->run_work, 0);
else {
unsigned int cpu;
@@ -851,9 +860,7 @@ void blk_mq_run_queues(struct request_queue *q, bool async)
test_bit(BLK_MQ_S_STOPPED, &hctx->state))
continue;

- preempt_disable();
blk_mq_run_hw_queue(hctx, async);
- preempt_enable();
}
}
EXPORT_SYMBOL(blk_mq_run_queues);
@@ -880,9 +887,7 @@ void blk_mq_start_hw_queue(struct blk_mq_hw_ctx *hctx)
{
clear_bit(BLK_MQ_S_STOPPED, &hctx->state);

- preempt_disable();
blk_mq_run_hw_queue(hctx, false);
- preempt_enable();
}
EXPORT_SYMBOL(blk_mq_start_hw_queue);

@@ -907,9 +912,7 @@ void blk_mq_start_stopped_hw_queues(struct request_queue *q, bool async)
continue;

clear_bit(BLK_MQ_S_STOPPED, &hctx->state);
- preempt_disable();
blk_mq_run_hw_queue(hctx, async);
- preempt_enable();
}
}
EXPORT_SYMBOL(blk_mq_start_stopped_hw_queues);
--
2.1.0



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