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/* per device */
struct ioc {
	struct rq_qos			rqos;

	bool				enabled;

	struct ioc_params		params;
	struct ioc_margins		margins;
	u32				period_us;
	u32				timer_slack_ns;
	u64				vrate_min;
	u64				vrate_max;

	spinlock_t			lock;
	struct timer_list		timer;
	struct list_head		active_iocgs;	/* active cgroups */
	struct ioc_pcpu_stat __percpu	*pcpu_stat;

	enum ioc_running		running;
	atomic64_t			vtime_rate;
	u64				vtime_base_rate;
	s64				vtime_err;

	seqcount_spinlock_t		period_seqcount;
	u64				period_at;	/* wallclock starttime */
	u64				period_at_vtime; /* vtime starttime */

	atomic64_t			cur_period;	/* inc'd each period */
	int				busy_level;	/* saturation history */

	bool				weights_updated;
	atomic_t			hweight_gen;	/* for lazy hweights */

	/* debt forgivness */
	u64				dfgv_period_at;
	u64				dfgv_period_rem;
	u64				dfgv_usage_us_sum;

	u64				autop_too_fast_at;
	u64				autop_too_slow_at;
	int				autop_idx;
	bool				user_qos_params:1;
	bool				user_cost_model:1;
};
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/* per device-cgroup pair */
struct ioc_gq {
	struct blkg_policy_data		pd;
	struct ioc			*ioc;

	/*
	 * A iocg can get its weight from two sources - an explicit
	 * per-device-cgroup configuration or the default weight of the
	 * cgroup.  `cfg_weight` is the explicit per-device-cgroup
	 * configuration.  `weight` is the effective considering both
	 * sources.
	 *
	 * When an idle cgroup becomes active its `active` goes from 0 to
	 * `weight`.  `inuse` is the surplus adjusted active weight.
	 * `active` and `inuse` are used to calculate `hweight_active` and
	 * `hweight_inuse`.
	 *
	 * `last_inuse` remembers `inuse` while an iocg is idle to persist
	 * surplus adjustments.
	 *
	 * `inuse` may be adjusted dynamically during period. `saved_*` are used
	 * to determine and track adjustments.
	 */
  
	u32				cfg_weight;
	u32				weight;
	u32				active;
	u32				inuse;

	u32				last_inuse;
	s64				saved_margin;

	sector_t			cursor;		/* to detect randio */

	/*
	 * `vtime` is this iocg's vtime cursor which progresses as IOs are
	 * issued.  If lagging behind device vtime, the delta represents
	 * the currently available IO budget.  If running ahead, the
	 * overage.
	 *
	 * `vtime_done` is the same but progressed on completion rather
	 * than issue.  The delta behind `vtime` represents the cost of
	 * currently in-flight IOs.
	 */
	atomic64_t			vtime;
	atomic64_t			done_vtime;
	u64				abs_vdebt;

	/* current delay in effect and when it started */
	u64				delay;
	u64				delay_at;

	/*
	 * The period this iocg was last active in.  Used for deactivation
	 * and invalidating `vtime`.
	 */
	atomic64_t			active_period;
	struct list_head		active_list;

	/* see __propagate_weights() and current_hweight() for details */
	u64				child_active_sum;
	u64				child_inuse_sum;
	u64				child_adjusted_sum;
	int				hweight_gen;
	u32				hweight_active;
	u32				hweight_inuse;
	u32				hweight_donating;
	u32				hweight_after_donation;

	struct list_head		walk_list;
	struct list_head		surplus_list;

	struct wait_queue_head		waitq;
	struct hrtimer			waitq_timer;

	/* timestamp at the latest activation */
	u64				activated_at;

	/* statistics */
	struct iocg_pcpu_stat __percpu	*pcpu_stat;
	struct iocg_stat		stat;
	struct iocg_stat		last_stat;
	u64				last_stat_abs_vusage;
	u64				usage_delta_us;
	u64				wait_since;
	u64				indebt_since;
	u64				indelay_since;

	/* this iocg's depth in the hierarchy and ancestors including self */
	int				level;
	struct ioc_gq			*ancestors[];
};

Y_4K/y_b = a + b* X_4K / X_b

Y_4k = a* X_4k Y_b / X_b. a= Y_4k * X_b / (X_4ky_b)

Ssd iops: a_8k= 70k8k / (4k51k) = 2.745

a_16k = 70k * 16k / ( 29k * 4k) =

y = a+ bx + cx2

IOPS = y/x = 70M/x + 60 - 2 * x

BPS = 70M + 60x - 2x^2

270M = a + b * 4k + c * 16M

400M = a + b * 8k + c * 64M

460M = a + b * 16k + c * 256M

130M = 4k * b+ c * 48M

60M = 8k * b + c * 192M

200M = - c * 96M

c= -2.08

b = 57.42k

a = 460M - 918.72M + 532.48M = 74M

(y_4k, 4k).