Re: [PATCH RFC v7 02/12] blk-mq: rename blk_mq_update_tag_set_depth()

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On 10/08/2020 17:51, Kashyap Desai wrote:
tx context.
Hannes/John - We need one more correction for below patch -

https://github.com/hisilicon/kernel-dev/commit/ff631eb80aa0449eaeb78a282fd7eff2a9e42f77

I noticed - that elevator_queued count goes negative mainly because there
are some case where IO was submitted from dispatch queue(not scheduler
queue) and request still has "RQF_ELVPRIV" flag set.
In such cases " dd_finish_request" is called without " dd_insert_request". I
think it is better to decrement counter once it is taken out from dispatched
queue. (Ming proposed to use dispatch path for decrementing counter, but I
somehow did not accounted assuming RQF_ELVPRIV will be set only if IO is
submitted from scheduler queue.)

Below is additional change. Can you merge this ?

diff --git a/block/mq-deadline.c b/block/mq-deadline.c
index 9d75374..bc413dd 100644
--- a/block/mq-deadline.c
+++ b/block/mq-deadline.c
@@ -385,6 +385,8 @@ static struct request *dd_dispatch_request(struct
blk_mq_hw_ctx *hctx)

         spin_lock(&dd->lock);
         rq = __dd_dispatch_request(dd);
+       if (rq)
+               atomic_dec(&rq->mq_hctx->elevator_queued);

Is there any reason why this operation could not be taken outside the spinlock? I assume raciness is not a problem with this patch...

         spin_unlock(&dd->lock);

         return rq;
@@ -574,7 +576,6 @@ static void dd_finish_request(struct request *rq)
                         blk_mq_sched_mark_restart_hctx(rq->mq_hctx);
                 spin_unlock_irqrestore(&dd->zone_lock, flags);
         }
-       atomic_dec(&rq->mq_hctx->elevator_queued);
  }

  static bool dd_has_work(struct blk_mq_hw_ctx *hctx)
--
2.9.5

Kashyap
.#


btw, can you provide signed-off-by if you want credit upgraded to Co-developed-by?

Thanks,
john



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