Commit d7790b92 authored Feb 06, 2014 by Shlomo Pongratz Committed by Jens Axboe Feb 07, 2014

block/null_blk: Fix completion processing from LIFO to FIFO

The completion queue is implemented using lockless list.

The llist_add is adds the events to the list head which is a push operation.
The processing of the completion elements is done by disconnecting all the
pushed elements and iterating over the disconnected list. The problem is
that the processing is done in reverse order w.r.t order of the insertion
i.e. LIFO processing. By reversing the disconnected list which is done in
linear time the desired FIFO processing is achieved.

Signed-off-by: Shlomo Pongratz <shlomop@mellanox.com>
Signed-off-by: Jens Axboe <axboe@fb.com>

parent 5cb8850c

drivers/block/null_blk.c

+2 −0

Original line number	Diff line number	Diff line
		@@ -195,6 +195,7 @@ static enum hrtimer_restart null_cmd_timer_expired(struct hrtimer *timer)
		cq = &per_cpu(completion_queues, smp_processor_id());

		while ((entry = llist_del_all(&cq->list)) != NULL) {
		entry = llist_reverse_order(entry);
		do {
		cmd = container_of(entry, struct nullb_cmd, ll_list);
		end_cmd(cmd);
		@@ -235,6 +236,7 @@ static void null_ipi_cmd_end_io(void *data)
		cq = &per_cpu(completion_queues, smp_processor_id());

		entry = llist_del_all(&cq->list);
		entry = llist_reverse_order(entry);

		while (entry) {
		next = entry->next;

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