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authorMing Lei <ming.lei@redhat.com>2017-11-02 23:24:38 +0800
committerJens Axboe <axboe@kernel.dk>2017-11-04 12:40:13 -0600
commit923218f6166a84688973acdc39094f3bee1e9ad4 (patch)
tree1013b8c39764532780292633f7e4214c99480aaf /block/blk-mq-sched.c
parent244c65a3ccaa06fd15cc940315606674d3108b2f (diff)
downloadlinux-923218f6166a84688973acdc39094f3bee1e9ad4.tar.bz2
blk-mq: don't allocate driver tag upfront for flush rq
The idea behind it is simple: 1) for none scheduler, driver tag has to be borrowed for flush rq, otherwise we may run out of tag, and that causes an IO hang. And get/put driver tag is actually noop for none, so reordering tags isn't necessary at all. 2) for a real I/O scheduler, we need not allocate a driver tag upfront for flush rq. It works just fine to follow the same approach as normal requests: allocate driver tag for each rq just before calling ->queue_rq(). One driver visible change is that the driver tag isn't shared in the flush request sequence. That won't be a problem, since we always do that in legacy path. Then flush rq need not be treated specially wrt. get/put driver tag. This cleans up the code - for instance, reorder_tags_to_front() can be removed, and we needn't worry about request ordering in dispatch list for avoiding I/O deadlock. Also we have to put the driver tag before requeueing. Signed-off-by: Ming Lei <ming.lei@redhat.com> Signed-off-by: Jens Axboe <axboe@kernel.dk>
Diffstat (limited to 'block/blk-mq-sched.c')
-rw-r--r--block/blk-mq-sched.c42
1 files changed, 5 insertions, 37 deletions
diff --git a/block/blk-mq-sched.c b/block/blk-mq-sched.c
index e7094f44afaf..01a43fed6b8c 100644
--- a/block/blk-mq-sched.c
+++ b/block/blk-mq-sched.c
@@ -356,29 +356,12 @@ static bool blk_mq_sched_bypass_insert(struct blk_mq_hw_ctx *hctx,
return true;
}
- if (has_sched) {
+ if (has_sched)
rq->rq_flags |= RQF_SORTED;
- WARN_ON(rq->tag != -1);
- }
return false;
}
-/*
- * Add flush/fua to the queue. If we fail getting a driver tag, then
- * punt to the requeue list. Requeue will re-invoke us from a context
- * that's safe to block from.
- */
-static void blk_mq_sched_insert_flush(struct blk_mq_hw_ctx *hctx,
- struct request *rq, bool can_block)
-{
- if (blk_mq_get_driver_tag(rq, &hctx, can_block)) {
- blk_insert_flush(rq);
- blk_mq_run_hw_queue(hctx, true);
- } else
- blk_mq_add_to_requeue_list(rq, false, true);
-}
-
void blk_mq_sched_insert_request(struct request *rq, bool at_head,
bool run_queue, bool async, bool can_block)
{
@@ -389,10 +372,12 @@ void blk_mq_sched_insert_request(struct request *rq, bool at_head,
/* flush rq in flush machinery need to be dispatched directly */
if (!(rq->rq_flags & RQF_FLUSH_SEQ) && op_is_flush(rq->cmd_flags)) {
- blk_mq_sched_insert_flush(hctx, rq, can_block);
- return;
+ blk_insert_flush(rq);
+ goto run;
}
+ WARN_ON(e && (rq->tag != -1));
+
if (blk_mq_sched_bypass_insert(hctx, !!e, rq))
goto run;
@@ -419,23 +404,6 @@ void blk_mq_sched_insert_requests(struct request_queue *q,
struct blk_mq_hw_ctx *hctx = blk_mq_map_queue(q, ctx->cpu);
struct elevator_queue *e = hctx->queue->elevator;
- if (e) {
- struct request *rq, *next;
-
- /*
- * We bypass requests that already have a driver tag assigned,
- * which should only be flushes. Flushes are only ever inserted
- * as single requests, so we shouldn't ever hit the
- * WARN_ON_ONCE() below (but let's handle it just in case).
- */
- list_for_each_entry_safe(rq, next, list, queuelist) {
- if (WARN_ON_ONCE(rq->tag != -1)) {
- list_del_init(&rq->queuelist);
- blk_mq_sched_bypass_insert(hctx, true, rq);
- }
- }
- }
-
if (e && e->type->ops.mq.insert_requests)
e->type->ops.mq.insert_requests(hctx, list, false);
else