Messages in this thread Patch in this message | | | From | Pavel Begunkov <> | Subject | [PATCH 2/2] block: kill extra rcu lock/unlock in queue enter | Date | Wed, 20 Oct 2021 21:03:19 +0100 |
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blk_try_enter_queue() already takes rcu_read_lock/unlock, so we can avoid the second pair in percpu_ref_tryget_live(), use a newly added percpu_ref_tryget_live_rcu().
As rcu_read_lock/unlock imply barrier()s, it's pretty noticeable, especially for for !CONFIG_PREEMPT_RCU (default for some distributions), where __rcu_read_lock/unlock() are not inlined.
3.20% io_uring [kernel.vmlinux] [k] __rcu_read_unlock 3.05% io_uring [kernel.vmlinux] [k] __rcu_read_lock
2.52% io_uring [kernel.vmlinux] [k] __rcu_read_unlock 2.28% io_uring [kernel.vmlinux] [k] __rcu_read_lock
Signed-off-by: Pavel Begunkov <asml.silence@gmail.com> --- block/blk-core.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-)
diff --git a/block/blk-core.c b/block/blk-core.c index 88752e51d2b6..20e76aeb50f5 100644 --- a/block/blk-core.c +++ b/block/blk-core.c @@ -389,7 +389,7 @@ EXPORT_SYMBOL(blk_cleanup_queue); static bool blk_try_enter_queue(struct request_queue *q, bool pm) { rcu_read_lock(); - if (!percpu_ref_tryget_live(&q->q_usage_counter)) + if (!percpu_ref_tryget_live_rcu(&q->q_usage_counter)) goto fail; /* -- 2.33.1
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