Commit ab8df828 authored by Tejun Heo's avatar Tejun Heo Committed by Jens Axboe
Browse files

iocost: factor out ioc_forgive_debts() 



Debt reduction logic is going to be improved and expanded. Factor it out
into ioc_forgive_debts() and generalize the comment a bit. No functional
change.

Signed-off-by: default avatarTejun Heo <tj@kernel.org>
Signed-off-by: default avatarJens Axboe <axboe@kernel.dk>
parent 6abc4946

block/blk-iocost.c

+35 −31
Original line number Diff line number Diff line
@@ -1979,6 +1979,40 @@ static void transfer_surpluses(struct list_head *surpluses, struct ioc_now *now) 
		list_del_init(&iocg->walk_list);

}



/*

 * A low weight iocg can amass a large amount of debt, for example, when

 * anonymous memory gets reclaimed aggressively. If the system has a lot of

 * memory paired with a slow IO device, the debt can span multiple seconds or

 * more. If there are no other subsequent IO issuers, the in-debt iocg may end

 * up blocked paying its debt while the IO device is idle.

 *

 * The following protects against such cases. If the device has been

 * sufficiently idle for a while, the debts are halved.

 */

static void ioc_forgive_debts(struct ioc *ioc, u64 usage_us_sum, int nr_debtors,

			      int nr_shortages, struct ioc_now *now)

{

	if (nr_shortages ||

	    div64_u64(100 * usage_us_sum, now->now - ioc->period_at) >=

	    DEBT_BUSY_USAGE_PCT)

		ioc->debt_busy_at = now->now;



	if (nr_debtors &&

	    now->now - ioc->debt_busy_at >= DEBT_REDUCTION_IDLE_DUR) {

		struct ioc_gq *iocg;



		list_for_each_entry(iocg, &ioc->active_iocgs, active_list) {

			if (iocg->abs_vdebt) {

				spin_lock(&iocg->waitq.lock);

				iocg->abs_vdebt /= 2;

				iocg_kick_waitq(iocg, true, now);

				spin_unlock(&iocg->waitq.lock);

			}

		}

		ioc->debt_busy_at = now->now;

	}

}



static void ioc_timer_fn(struct timer_list *timer)

{

	struct ioc *ioc = container_of(timer, struct ioc, timer);
@@ -2171,37 +2205,7 @@ static void ioc_timer_fn(struct timer_list *timer) 
	list_for_each_entry_safe(iocg, tiocg, &surpluses, surplus_list)

		list_del_init(&iocg->surplus_list);



	/*

	 * A low weight iocg can amass a large amount of debt, for example, when

	 * anonymous memory gets reclaimed aggressively. If the system has a lot

	 * of memory paired with a slow IO device, the debt can span multiple

	 * seconds or more. If there are no other subsequent IO issuers, the

	 * in-debt iocg may end up blocked paying its debt while the IO device

	 * is idle.

	 *

	 * The following protects against such pathological cases. If the device

	 * has been sufficiently idle for a substantial amount of time, the

	 * debts are halved. The criteria are on the conservative side as we

	 * want to resolve the rare extreme cases without impacting regular

	 * operation by forgiving debts too readily.

	 */

	if (nr_shortages ||

	    div64_u64(100 * usage_us_sum, now.now - ioc->period_at) >=

	    DEBT_BUSY_USAGE_PCT)

		ioc->debt_busy_at = now.now;



	if (nr_debtors &&

	    now.now - ioc->debt_busy_at >= DEBT_REDUCTION_IDLE_DUR) {

		list_for_each_entry(iocg, &ioc->active_iocgs, active_list) {

			if (iocg->abs_vdebt) {

				spin_lock(&iocg->waitq.lock);

				iocg->abs_vdebt /= 2;

				iocg_kick_waitq(iocg, true, &now);

				spin_unlock(&iocg->waitq.lock);

			}

		}

		ioc->debt_busy_at = now.now;

	}

	ioc_forgive_debts(ioc, usage_us_sum, nr_debtors, nr_shortages, &now);



	/*

	 * If q is getting clogged or we're missing too much, we're issuing

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