void blk_account_io_done(struct request *req, u64 now)
{
	/*
	 * Account IO completion.  flush_rq isn't accounted as a
	 * normal IO on queueing nor completion.  Accounting the
	 * containing request is enough.
	 */
	if (blk_do_io_stat(req) && !(req->rq_flags & RQF_FLUSH_SEQ)) {
		const int sgrp = op_stat_group(req_op(req));
		struct hd_struct *part;

		part_stat_lock();
		part = req->part;

		update_io_ticks(part, jiffies);
		part_stat_inc(part, ios[sgrp]);
		part_stat_add(part, nsecs[sgrp], now - req->start_time_ns);
		part_stat_add(part, time_in_queue, nsecs_to_jiffies64(now - req->start_time_ns));
		part_dec_in_flight(req->q, part, rq_data_dir(req));

		hd_struct_put(part);
		part_stat_unlock();
	}
}
void blk_account_io_done(struct request *req, u64 now)
{
	 
	if (blk_do_io_stat(req) && !(req->rq_flags & RQF_FLUSH_SEQ)) {
		const int sgrp = op_stat_group(req_op(req));
		struct hd_struct *part;

		part_stat_lock();
		part = req->part;

		update_io_ticks(part, jiffies);
		part_stat_inc(part, ios[sgrp]);
		part_stat_add(part, nsecs[sgrp], now - req->start_time_ns);
		part_stat_add(part, time_in_queue, nsecs_to_jiffies64(now - req->start_time_ns));
		part_dec_in_flight(req->q, part, rq_data_dir(req));

		hd_struct_put(part);
		part_stat_unlock();
	}
}