Re: [PATCH] cfq-iosched: requests "in flight" vs "in driver"clarification

[Vivek Goyal]

On Sat, Feb 27, 2010 at 05:03:09PM +0100, Corrado Zoccolo wrote:
> Counters for requests "in flight" and "in driver" are used asymmetrically
> in cfq_may_dispatch, and have slightly different meaning.
> We split the rq_in_flight counter (was sync_flight) to count both sync
> and async requests, in order to use this one, which is more accurate in
> some corner cases.
> The rq_in_driver counter is coalesced, since individual sync/async counts
> are not used any more.
> 
> Signed-off-by: Corrado Zoccolo <czoccolo@xxxxxxxxx>
> ---
>  block/cfq-iosched.c |   44 ++++++++++++++++++--------------------------
>  1 files changed, 18 insertions(+), 26 deletions(-)
> 
> diff --git a/block/cfq-iosched.c b/block/cfq-iosched.c
> index 10eb286..eed649c 100644
> --- a/block/cfq-iosched.c
> +++ b/block/cfq-iosched.c
> @@ -223,8 +223,8 @@ struct cfq_data {
>  
>  	unsigned int busy_queues;
>  
> -	int rq_in_driver[2];
> -	int sync_flight;
> +	int rq_in_driver;
> +	int rq_in_flight[2];
>  
>  	/*
>  	 * queue-depth detection
> @@ -417,11 +417,6 @@ static struct cfq_queue *cfq_get_queue(struct cfq_data *, bool,
>  static struct cfq_io_context *cfq_cic_lookup(struct cfq_data *,
>  						struct io_context *);
>  
> -static inline int rq_in_driver(struct cfq_data *cfqd)
> -{
> -	return cfqd->rq_in_driver[0] + cfqd->rq_in_driver[1];
> -}
> -
>  static inline struct cfq_queue *cic_to_cfqq(struct cfq_io_context *cic,
>  					    bool is_sync)
>  {
> @@ -1415,9 +1410,9 @@ static void cfq_activate_request(struct request_queue *q, struct request *rq)
>  {
>  	struct cfq_data *cfqd = q->elevator->elevator_data;
>  
> -	cfqd->rq_in_driver[rq_is_sync(rq)]++;
> +	cfqd->rq_in_driver++;
>  	cfq_log_cfqq(cfqd, RQ_CFQQ(rq), "activate rq, drv=%d",
> -						rq_in_driver(cfqd));
> +						cfqd->rq_in_driver);
>  
>  	cfqd->last_position = blk_rq_pos(rq) + blk_rq_sectors(rq);
>  }
> @@ -1425,12 +1420,11 @@ static void cfq_activate_request(struct request_queue *q, struct request *rq)
>  static void cfq_deactivate_request(struct request_queue *q, struct request *rq)
>  {
>  	struct cfq_data *cfqd = q->elevator->elevator_data;
> -	const int sync = rq_is_sync(rq);
>  
> -	WARN_ON(!cfqd->rq_in_driver[sync]);
> -	cfqd->rq_in_driver[sync]--;
> +	WARN_ON(!cfqd->rq_in_driver);
> +	cfqd->rq_in_driver--;
>  	cfq_log_cfqq(cfqd, RQ_CFQQ(rq), "deactivate rq, drv=%d",
> -						rq_in_driver(cfqd));
> +						cfqd->rq_in_driver);
>  }
>  
>  static void cfq_remove_request(struct request *rq)
> @@ -1873,8 +1867,7 @@ static void cfq_dispatch_insert(struct request_queue *q, struct request *rq)
>  	cfqq->dispatched++;
>  	elv_dispatch_sort(q, rq);
>  
> -	if (cfq_cfqq_sync(cfqq))
> -		cfqd->sync_flight++;
> +	cfqd->rq_in_flight[cfq_cfqq_sync(cfqq)]++;
>  	cfqq->nr_sectors += blk_rq_sectors(rq);
>  }
>  
> @@ -2221,13 +2214,13 @@ static bool cfq_may_dispatch(struct cfq_data *cfqd, struct cfq_queue *cfqq)
>  	/*
>  	 * Drain async requests before we start sync IO
>  	 */
> -	if (cfq_should_idle(cfqd, cfqq) && cfqd->rq_in_driver[BLK_RW_ASYNC])
> +	if (cfq_should_idle(cfqd, cfqq) && cfqd->rq_in_flight[BLK_RW_ASYNC])
>  		return false;
>  

So we need to make sure there are no async requests either in dispatch
queue or driver. So rq_in_flight is better than just plain rq_in_driver.

Makes sense.

Acked-by: Vivek Goyal <vgoyal@xxxxxxxxxx>

Thanks
Vivek
 
>  	/*
>  	 * If this is an async queue and we have sync IO in flight, let it wait
>  	 */
> -	if (cfqd->sync_flight && !cfq_cfqq_sync(cfqq))
> +	if (cfqd->rq_in_flight[BLK_RW_SYNC] && !cfq_cfqq_sync(cfqq))
>  		return false;
>  
>  	max_dispatch = cfqd->cfq_quantum;
> @@ -3210,14 +3203,14 @@ static void cfq_update_hw_tag(struct cfq_data *cfqd)
>  {
>  	struct cfq_queue *cfqq = cfqd->active_queue;
>  
> -	if (rq_in_driver(cfqd) > cfqd->hw_tag_est_depth)
> -		cfqd->hw_tag_est_depth = rq_in_driver(cfqd);
> +	if (cfqd->rq_in_driver > cfqd->hw_tag_est_depth)
> +		cfqd->hw_tag_est_depth = cfqd->rq_in_driver;
>  
>  	if (cfqd->hw_tag == 1)
>  		return;
>  
>  	if (cfqd->rq_queued <= CFQ_HW_QUEUE_MIN &&
> -	    rq_in_driver(cfqd) <= CFQ_HW_QUEUE_MIN)
> +	    cfqd->rq_in_driver <= CFQ_HW_QUEUE_MIN)
>  		return;
>  
>  	/*
> @@ -3227,7 +3220,7 @@ static void cfq_update_hw_tag(struct cfq_data *cfqd)
>  	 */
>  	if (cfqq && cfq_cfqq_idle_window(cfqq) &&
>  	    cfqq->dispatched + cfqq->queued[0] + cfqq->queued[1] <
> -	    CFQ_HW_QUEUE_MIN && rq_in_driver(cfqd) < CFQ_HW_QUEUE_MIN)
> +	    CFQ_HW_QUEUE_MIN && cfqd->rq_in_driver < CFQ_HW_QUEUE_MIN)
>  		return;
>  
>  	if (cfqd->hw_tag_samples++ < 50)
> @@ -3280,13 +3273,12 @@ static void cfq_completed_request(struct request_queue *q, struct request *rq)
>  
>  	cfq_update_hw_tag(cfqd);
>  
> -	WARN_ON(!cfqd->rq_in_driver[sync]);
> +	WARN_ON(!cfqd->rq_in_driver);
>  	WARN_ON(!cfqq->dispatched);
> -	cfqd->rq_in_driver[sync]--;
> +	cfqd->rq_in_driver--;
>  	cfqq->dispatched--;
>  
> -	if (cfq_cfqq_sync(cfqq))
> -		cfqd->sync_flight--;
> +	cfqd->rq_in_flight[cfq_cfqq_sync(cfqq)]--;
>  
>  	if (sync) {
>  		RQ_CIC(rq)->last_end_request = now;
> @@ -3340,7 +3332,7 @@ static void cfq_completed_request(struct request_queue *q, struct request *rq)
>  		}
>  	}
>  
> -	if (!rq_in_driver(cfqd))
> +	if (!cfqd->rq_in_driver)
>  		cfq_schedule_dispatch(cfqd);
>  }
>  
> -- 
> 1.6.4.4
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