[PATCH] NVMe: Adhere to request queue block accounting enable/disable

[Keith Busch]

The diff looks like the inverse of what you meant to send. :)

On Fri, 9 May 2014, Sam Bradshaw wrote:
> Recently, a new sysfs control "iostats" was added to selectively
> enable or disable io statistics collection for request queues.  This
> patch hooks that control.
>
> IO statistics collection is rather expensive on large, multi-node
> machines with drives pushing millions of iops.  Having the ability to
> disable collection if not needed can improve throughput significantly.
>
> As a data point, on a quad E5-4640, I see more than 50% throughput
> improvement when io statistics accounting is disabled during heavily
> multi-threaded small block random read benchmarks where device
> performance is in the million iops+ range.
>
> Signed-off-by: Sam Bradshaw <sbradshaw at micron.com>
> ---
> diff --git a/drivers/block/nvme-core.c b/drivers/block/nvme-core.c
> index 3a25502..cd8a8bc 100644
> --- a/drivers/block/nvme-core.c
> +++ b/drivers/block/nvme-core.c
> @@ -383,30 +383,25 @@ void nvme_free_iod(struct nvme_dev *dev, struct nvme_iod *iod)
> static void nvme_start_io_acct(struct bio *bio)
> {
> 	struct gendisk *disk = bio->bi_bdev->bd_disk;
> -	if (blk_queue_io_stat(disk->queue)) {
> -		const int rw = bio_data_dir(bio);
> -		int cpu = part_stat_lock();
> -		part_round_stats(cpu, &disk->part0);
> -		part_stat_inc(cpu, &disk->part0, ios[rw]);
> -		part_stat_add(cpu, &disk->part0, sectors[rw],
> -							bio_sectors(bio));
> -		part_inc_in_flight(&disk->part0, rw);
> -		part_stat_unlock();
> -	}
> +	const int rw = bio_data_dir(bio);
> +	int cpu = part_stat_lock();
> +	part_round_stats(cpu, &disk->part0);
> +	part_stat_inc(cpu, &disk->part0, ios[rw]);
> +	part_stat_add(cpu, &disk->part0, sectors[rw], bio_sectors(bio));
> +	part_inc_in_flight(&disk->part0, rw);
> +	part_stat_unlock();
> }
>
> static void nvme_end_io_acct(struct bio *bio, unsigned long start_time)
> {
> 	struct gendisk *disk = bio->bi_bdev->bd_disk;
> -	if (blk_queue_io_stat(disk->queue)) {
> -		const int rw = bio_data_dir(bio);
> -		unsigned long duration = jiffies - start_time;
> -		int cpu = part_stat_lock();
> -		part_stat_add(cpu, &disk->part0, ticks[rw], duration);
> -		part_round_stats(cpu, &disk->part0);
> -		part_dec_in_flight(&disk->part0, rw);
> -		part_stat_unlock();
> -	}
> +	const int rw = bio_data_dir(bio);
> +	unsigned long duration = jiffies - start_time;
> +	int cpu = part_stat_lock();
> +	part_stat_add(cpu, &disk->part0, ticks[rw], duration);
> +	part_round_stats(cpu, &disk->part0);
> +	part_dec_in_flight(&disk->part0, rw);
> +	part_stat_unlock();
> }
>
> static void bio_completion(struct nvme_queue *nvmeq, void *ctx,