Messages in this thread | | | Subject | Re: [PATCH] blk-mq: Fix blk_mq_tagset_busy_iter() for shared tags | From | John Garry <> | Date | Mon, 18 Oct 2021 09:08:57 +0100 |
| |
On 13/10/2021 16:13, John Garry wrote: >> diff --git a/block/blk-mq-tag.c b/block/blk-mq-tag.c >> index 72a2724a4eee..2a2ad6dfcc33 100644 >> --- a/block/blk-mq-tag.c >> +++ b/block/blk-mq-tag.c >> @@ -232,8 +232,9 @@ static bool bt_iter(struct sbitmap *bitmap, >> unsigned int bitnr, void *data) >> if (!rq) >> return true; >> - if (rq->q == hctx->queue && rq->mq_hctx == hctx) >> - ret = iter_data->fn(hctx, rq, iter_data->data, reserved); >> + if (rq->q == hctx->queue && (rq->mq_hctx == hctx || >> + blk_mq_is_shared_tags(hctx->flags))) >> + ret = iter_data->fn(rq->mq_hctx, rq, iter_data->data, reserved); >> blk_mq_put_rq_ref(rq); >> return ret; >> } >> @@ -460,6 +461,9 @@ void blk_mq_queue_tag_busy_iter(struct >> request_queue *q, busy_iter_fn *fn, >> if (tags->nr_reserved_tags) >> bt_for_each(hctx, &tags->breserved_tags, fn, priv, true); >> bt_for_each(hctx, &tags->bitmap_tags, fn, priv, false); >> + >> + if (blk_mq_is_shared_tags(hctx->flags)) >> + break; >> } >> blk_queue_exit(q); >> } >> > > I suppose that is ok, and means that we iter once. > > However, I have to ask, where is the big user of > blk_mq_queue_tag_busy_iter() coming from? I saw this from Kashyap's mail: > > > 1.31% 1.31% kworker/57:1H-k [kernel.vmlinux] > > native_queued_spin_lock_slowpath > > ret_from_fork > > kthread > > worker_thread > > process_one_work > > blk_mq_timeout_work > > blk_mq_queue_tag_busy_iter > > bt_iter > > blk_mq_find_and_get_req > > _raw_spin_lock_irqsave > > native_queued_spin_lock_slowpath > > How or why blk_mq_timeout_work()?
Just some update: I tried hisi_sas with 10x SAS SSDs, megaraid sas with 1x SATA HDD (that's all I have), and null blk with lots of devices, and I still can't see high usage of blk_mq_queue_tag_busy_iter().
So how about we get this patch processed (to fix blk_mq_tagset_busy_iter()), as it is independent of blk_mq_queue_tag_busy_iter()? And then wait for some update or some more info from Kashyap regarding blk_mq_queue_tag_busy_iter()
Thanks, John
| |