From c421a3eb2e27402c14131a14390551ae6cdb15fa Mon Sep 17 00:00:00 2001 From: Tejun Heo Date: Tue, 1 Sep 2020 14:52:51 -0400 Subject: [PATCH] blk-iocost: revamp debt handling Debt handling had several issues. * How much inuse a debtor carries wasn't clearly defined. inuse would be driven down over time from not issuing IOs but it'd be better to clamp it to minimum immediately once in debt. * How much can be paid off was determined by hweight_inuse. As inuse was driven down, the payment amount would fall together regardless of the debtor's active weight. This means that the debtors were punished harshly. * ioc_rqos_merge() wasn't calling blkcg_schedule_throttle() after iocg_kick_delay(). This patch revamps debt handling so that * Debt handling owns inuse for iocgs in debt and keeps them at zero. * Payment amount is determined by hweight_active. This is more deterministic and safer than hweight_inuse but still far from ideal in that it doesn't factor in possible donations from other iocgs for debt payments. This likely needs further improvements in the future. * iocg_rqos_merge() now calls blkcg_schedule_throttle() as necessary. Signed-off-by: Tejun Heo Cc: Andy Newell Signed-off-by: Jens Axboe --- block/blk-iocost.c | 117 +++++++++++++++++++++++++++++++++++---------- 1 file changed, 93 insertions(+), 24 deletions(-) diff --git a/block/blk-iocost.c b/block/blk-iocost.c index d09b4011449c..d2b69d87f3e7 100644 --- a/block/blk-iocost.c +++ b/block/blk-iocost.c @@ -1206,13 +1206,13 @@ static bool iocg_kick_delay(struct ioc_gq *iocg, struct ioc_now *now) struct blkcg_gq *blkg = iocg_to_blkg(iocg); u64 vtime = atomic64_read(&iocg->vtime); u64 delta_ns, expires, oexpires; - u32 hw_inuse; + u32 hwa; lockdep_assert_held(&iocg->waitq.lock); /* debt-adjust vtime */ - current_hweight(iocg, NULL, &hw_inuse); - vtime += abs_cost_to_cost(iocg->abs_vdebt, hw_inuse); + current_hweight(iocg, &hwa, NULL); + vtime += abs_cost_to_cost(iocg->abs_vdebt, hwa); /* * Clear or maintain depending on the overage. Non-zero vdebt is what @@ -1258,6 +1258,47 @@ static enum hrtimer_restart iocg_delay_timer_fn(struct hrtimer *timer) return HRTIMER_NORESTART; } +static void iocg_incur_debt(struct ioc_gq *iocg, u64 abs_cost, + struct ioc_now *now) +{ + struct iocg_pcpu_stat *gcs; + + lockdep_assert_held(&iocg->ioc->lock); + lockdep_assert_held(&iocg->waitq.lock); + WARN_ON_ONCE(list_empty(&iocg->active_list)); + + /* + * Once in debt, debt handling owns inuse. @iocg stays at the minimum + * inuse donating all of it share to others until its debt is paid off. + */ + if (!iocg->abs_vdebt && abs_cost) + propagate_weights(iocg, iocg->active, 0, false, now); + + iocg->abs_vdebt += abs_cost; + + gcs = get_cpu_ptr(iocg->pcpu_stat); + local64_add(abs_cost, &gcs->abs_vusage); + put_cpu_ptr(gcs); +} + +static void iocg_pay_debt(struct ioc_gq *iocg, u64 abs_vpay, + struct ioc_now *now) +{ + lockdep_assert_held(&iocg->ioc->lock); + lockdep_assert_held(&iocg->waitq.lock); + + /* make sure that nobody messed with @iocg */ + WARN_ON_ONCE(list_empty(&iocg->active_list)); + WARN_ON_ONCE(iocg->inuse > 1); + + iocg->abs_vdebt -= min(abs_vpay, iocg->abs_vdebt); + + /* if debt is paid in full, restore inuse */ + if (!iocg->abs_vdebt) + propagate_weights(iocg, iocg->active, iocg->last_inuse, + false, now); +} + static int iocg_wake_fn(struct wait_queue_entry *wq_entry, unsigned mode, int flags, void *key) { @@ -1296,26 +1337,25 @@ static void iocg_kick_waitq(struct ioc_gq *iocg, bool pay_debt, struct iocg_wake_ctx ctx = { .iocg = iocg }; u64 vshortage, expires, oexpires; s64 vbudget; - u32 hw_inuse; + u32 hwa; lockdep_assert_held(&iocg->waitq.lock); - current_hweight(iocg, NULL, &hw_inuse); + current_hweight(iocg, &hwa, NULL); vbudget = now->vnow - atomic64_read(&iocg->vtime); /* pay off debt */ if (pay_debt && iocg->abs_vdebt && vbudget > 0) { - u64 vdebt = abs_cost_to_cost(iocg->abs_vdebt, hw_inuse); - u64 delta = min_t(u64, vbudget, vdebt); - u64 abs_delta = min(cost_to_abs_cost(delta, hw_inuse), - iocg->abs_vdebt); + u64 abs_vbudget = cost_to_abs_cost(vbudget, hwa); + u64 abs_vpay = min_t(u64, abs_vbudget, iocg->abs_vdebt); + u64 vpay = abs_cost_to_cost(abs_vpay, hwa); lockdep_assert_held(&ioc->lock); - atomic64_add(delta, &iocg->vtime); - atomic64_add(delta, &iocg->done_vtime); - iocg->abs_vdebt -= abs_delta; - vbudget -= vdebt; + atomic64_add(vpay, &iocg->vtime); + atomic64_add(vpay, &iocg->done_vtime); + iocg_pay_debt(iocg, abs_vpay, now); + vbudget -= vpay; iocg_kick_delay(iocg, now); } @@ -1327,17 +1367,20 @@ static void iocg_kick_waitq(struct ioc_gq *iocg, bool pay_debt, * not positive. */ if (iocg->abs_vdebt) { - s64 vdebt = abs_cost_to_cost(iocg->abs_vdebt, hw_inuse); + s64 vdebt = abs_cost_to_cost(iocg->abs_vdebt, hwa); vbudget = min_t(s64, 0, vbudget - vdebt); } /* - * Wake up the ones which are due and see how much vtime we'll need - * for the next one. + * Wake up the ones which are due and see how much vtime we'll need for + * the next one. As paying off debt restores hw_inuse, it must be read + * after the above debt payment. */ - ctx.hw_inuse = hw_inuse; ctx.vbudget = vbudget; + current_hweight(iocg, NULL, &ctx.hw_inuse); + __wake_up_locked_key(&iocg->waitq, TASK_NORMAL, &ctx); + if (!waitqueue_active(&iocg->waitq)) return; if (WARN_ON_ONCE(ctx.vbudget >= 0)) @@ -1525,6 +1568,10 @@ static u32 hweight_after_donation(struct ioc_gq *iocg, u32 hwm, u32 usage, u64 vtime = atomic64_read(&iocg->vtime); s64 excess, delta, target, new_hwi; + /* debt handling owns inuse for debtors */ + if (iocg->abs_vdebt) + return 1; + /* see whether minimum margin requirement is met */ if (waitqueue_active(&iocg->waitq) || time_after64(vtime, now->vnow - ioc->margins.min)) @@ -1798,6 +1845,18 @@ static void transfer_surpluses(struct list_head *surpluses, struct ioc_now *now) struct ioc_gq *parent = iocg->ancestors[iocg->level - 1]; u32 inuse; + /* + * In-debt iocgs participated in the donation calculation with + * the minimum target hweight_inuse. Configuring inuse + * accordingly would work fine but debt handling expects + * @iocg->inuse stay at the minimum and we don't wanna + * interfere. + */ + if (iocg->abs_vdebt) { + WARN_ON_ONCE(iocg->inuse > 1); + continue; + } + /* w' = s' * b' / b'_p, note that b' == b'_t for donating leaves */ inuse = DIV64_U64_ROUND_UP( parent->child_adjusted_sum * iocg->hweight_after_donation, @@ -2081,6 +2140,10 @@ static u64 adjust_inuse_and_calc_cost(struct ioc_gq *iocg, u64 vtime, cost = abs_cost_to_cost(abs_cost, hwi); margin = now->vnow - vtime - cost; + /* debt handling owns inuse for debtors */ + if (iocg->abs_vdebt) + return cost; + /* * We only increase inuse during period and do so iff the margin has * deteriorated since the previous adjustment. @@ -2092,7 +2155,7 @@ static u64 adjust_inuse_and_calc_cost(struct ioc_gq *iocg, u64 vtime, spin_lock_irq(&ioc->lock); /* we own inuse only when @iocg is in the normal active state */ - if (list_empty(&iocg->active_list)) { + if (iocg->abs_vdebt || list_empty(&iocg->active_list)) { spin_unlock_irq(&ioc->lock); return cost; } @@ -2266,7 +2329,7 @@ retry_lock: * penalizing the cgroup and its descendants. */ if (use_debt) { - iocg->abs_vdebt += abs_cost; + iocg_incur_debt(iocg, abs_cost, &now); if (iocg_kick_delay(iocg, &now)) blkcg_schedule_throttle(rqos->q, (bio->bi_opf & REQ_SWAP) == REQ_SWAP); @@ -2275,7 +2338,7 @@ retry_lock: } /* guarantee that iocgs w/ waiters have maximum inuse */ - if (iocg->inuse != iocg->active) { + if (!iocg->abs_vdebt && iocg->inuse != iocg->active) { if (!ioc_locked) { iocg_unlock(iocg, false, &flags); ioc_locked = true; @@ -2363,14 +2426,20 @@ static void ioc_rqos_merge(struct rq_qos *rqos, struct request *rq, * be for the vast majority of cases. See debt handling in * ioc_rqos_throttle() for details. */ - spin_lock_irqsave(&iocg->waitq.lock, flags); + spin_lock_irqsave(&ioc->lock, flags); + spin_lock(&iocg->waitq.lock); + if (likely(!list_empty(&iocg->active_list))) { - iocg->abs_vdebt += abs_cost; - iocg_kick_delay(iocg, &now); + iocg_incur_debt(iocg, abs_cost, &now); + if (iocg_kick_delay(iocg, &now)) + blkcg_schedule_throttle(rqos->q, + (bio->bi_opf & REQ_SWAP) == REQ_SWAP); } else { iocg_commit_bio(iocg, bio, abs_cost, cost); } - spin_unlock_irqrestore(&iocg->waitq.lock, flags); + + spin_unlock(&iocg->waitq.lock); + spin_unlock_irqrestore(&ioc->lock, flags); } static void ioc_rqos_done_bio(struct rq_qos *rqos, struct bio *bio) -- 2.20.1