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blk-mq: Use llist_head for blk_cpu_done

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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 without additional locking.
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.

blk_mq_raise_softirq() needs a preempt-disable section to ensure the
request is enqueued on the same CPU as the softirq is raised.
Some callers (USB-storage) invoke this path in preemptible context.

Reviewed-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: Daniel Wagner <dwagner@suse.de>
Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
Signed-off-by: Jens Axboe <axboe@kernel.dk>
This commit is contained in:
Sebastian Andrzej Siewior
2021-01-23 21:10:27 +01:00
committed by Jens Axboe
parent 0a2efafbb1
commit f9ab49184a
2 changed files with 42 additions and 57 deletions
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2
include/linux/blkdev.h
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@@ -153,7 +153,7 @@ struct request {
*/
union {
struct hlist_node hash; /* merge hash */
struct list_head ipi_list;
struct llist_node ipi_list;
};
/*