[dm-devel] [PATCH 1/1] block: Convert hd_struct in_flight from atomic to percpu

[Jens Axboe]

On 06/28/2017 03:12 PM, Brian King wrote:
> -static inline int part_in_flight(struct hd_struct *part)
> +static inline unsigned long part_in_flight(struct hd_struct *part)
>  {
> -	return atomic_read(&part->in_flight[0]) + atomic_read(&part->in_flight[1]);
> +	return part_stat_read(part, in_flight[0]) + part_stat_read(part, in_flight[1]);

One obvious improvement would be to not do this twice, but only have to
loop once. Instead of making this an array, make it a structure with a
read and write count.

It still doesn't really fix the issue of someone running on a kernel
with a ton of possible CPUs configured. But it does reduce the overhead
by 50%.

-- 
Jens Axboe