Re: [PATCH RFC v3 01/22] blk-mq: Don't get budget for reserved requests

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On 27/10/2022 02:16, Damien Le Moal wrote:
Signed-off-by: John Garry<john.garry@xxxxxxxxxx>
---
  block/blk-mq.c          | 4 +++-
  drivers/scsi/scsi_lib.c | 3 ++-
  2 files changed, 5 insertions(+), 2 deletions(-)

diff --git a/block/blk-mq.c b/block/blk-mq.c
index 260adeb2e455..d8baabb32ea4 100644
--- a/block/blk-mq.c
+++ b/block/blk-mq.c
@@ -1955,11 +1955,13 @@ bool blk_mq_dispatch_rq_list(struct blk_mq_hw_ctx *hctx, struct list_head *list,
  	errors = queued = 0;
  	do {
  		struct blk_mq_queue_data bd;
+		bool need_budget;
rq = list_first_entry(list, struct request, queuelist); WARN_ON_ONCE(hctx != rq->mq_hctx);
-		prep = blk_mq_prep_dispatch_rq(rq, !nr_budgets);
+		need_budget = !nr_budgets && !blk_mq_is_reserved_rq(rq);
+		prep = blk_mq_prep_dispatch_rq(rq, need_budget);
  		if (prep != PREP_DISPATCH_OK)
  			break;
Below this code, there is:

		if (nr_budgets)
			nr_budgets--;

Don't you need to change that to:

		if (need_budget && nr_budgets)
			nr_budgets--;

? Otherwise, the accounting will be off.


Ah, yes, I think that you are right. I actually need to check nr_budgets usage further as nr_budgets initial value would be dependent on any reserved request requiring a budget (which we don't get).

Thanks,
John



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