On Mon, Jul 10, 2023 at 05:40:42PM +0000, Chuck Lever III wrote:
> > blk_rq_init_flush(rq);
> > - rq->flush.seq |= REQ_FSEQ_POSTFLUSH;
> > + rq->flush.seq |= REQ_FSEQ_PREFLUSH;
> > spin_lock_irq(&fq->mq_flush_lock);
> > list_move_tail(&rq->flush.list, &fq->flush_data_in_flight);
> > spin_unlock_irq(&fq->mq_flush_lock);
>
> Thanks for the quick response. No change.
I'm a bit lost and still can't reprodce. Below is a patch with the
only behavior differences I can find. It has two "#if 1" blocks,
which I'll need to bisect to to find out which made it work (if any,
but I hope so).
diff --git a/block/blk-mq.c b/block/blk-mq.c
index 5504719b970d59..67364e607f2d1d 100644
--- a/block/blk-mq.c
+++ b/block/blk-mq.c
@@ -2927,6 +2927,7 @@ void blk_mq_submit_bio(struct bio *bio)
struct request_queue *q = bdev_get_queue(bio->bi_bdev);
struct blk_plug *plug = blk_mq_plug(bio);
const int is_sync = op_is_sync(bio->bi_opf);
+ bool is_flush = op_is_flush(bio->bi_opf);
struct blk_mq_hw_ctx *hctx;
struct request *rq;
unsigned int nr_segs = 1;
@@ -2967,16 +2968,23 @@ void blk_mq_submit_bio(struct bio *bio)
return;
}
- if (op_is_flush(bio->bi_opf) && blk_insert_flush(rq))
- return;
-
- if (plug) {
- blk_add_rq_to_plug(plug, rq);
- return;
+#if 1 /* Variant 1, the plug is holding us back */
+ if (op_is_flush(bio->bi_opf)) {
+ if (blk_insert_flush(rq))
+ return;
+ } else {
+ if (plug) {
+ blk_add_rq_to_plug(plug, rq);
+ return;
+ }
}
+#endif
hctx = rq->mq_hctx;
if ((rq->rq_flags & RQF_USE_SCHED) ||
+#if 1 /* Variant 2 (unlikely), blk_mq_try_issue_directly causes problems */
+ is_flush ||
+#endif
(hctx->dispatch_busy && (q->nr_hw_queues == 1 || !is_sync))) {
blk_mq_insert_request(rq, 0);
blk_mq_run_hw_queue(hctx, true);
