[dm-devel] [PATCH v2 4/6] block: switch to per-cpu in-flight counters

[Jens Axboe]

On 11/30/18 3:22 PM, Mike Snitzer wrote:
> diff --git a/block/genhd.c b/block/genhd.c
> index cdf174d7d329..d4c9dd65def6 100644
> --- a/block/genhd.c
> +++ b/block/genhd.c
> @@ -45,53 +45,76 @@ static void disk_add_events(struct gendisk *disk);
>  static void disk_del_events(struct gendisk *disk);
>  static void disk_release_events(struct gendisk *disk);
>  
> -void part_inc_in_flight(struct request_queue *q, struct hd_struct *part, int rw)
> +void part_inc_in_flight(struct request_queue *q, int cpu, struct hd_struct *part, int rw)
>  {
>  	if (queue_is_mq(q))
>  		return;
>  
> -	atomic_inc(&part->in_flight[rw]);
> +	local_inc(&per_cpu_ptr(part->dkstats, cpu)->in_flight[rw]);

I mentioned this in a previous email, but why isn't this just using
this_cpu_inc? There's also no need to pass in the cpu, if we're not
running with preempt disabled already we have a problem.

-- 
Jens Axboe