diff options
author | Tejun Heo <tj@kernel.org> | 2020-09-01 21:52:49 +0300 |
---|---|---|
committer | Jens Axboe <axboe@kernel.dk> | 2020-09-02 04:38:32 +0300 |
commit | f1de2439ec43b74764f2a26e3a310b24407e3bde (patch) | |
tree | c42035bc380c37d789064168f9b16f282ae99779 | |
parent | e08d02aa5fc9978ed42240bd80d3fb5dd28ecac0 (diff) | |
download | linux-f1de2439ec43b74764f2a26e3a310b24407e3bde.tar.xz |
blk-iocost: revamp donation amount determination
iocost has various safety nets to combat inuse adjustment calculation
inaccuracies. With Andy's method implemented in transfer_surpluses(), inuse
adjustment calculations are now accurate and we can make donation amount
determinations accurate too.
* Stop keeping track of past usage history and using the maximum. Act on the
immediate usage information.
* Remove donation constraints defined by SURPLUS_* constants. Donate
whatever isn't used.
* Determine the donation amount so that the iocg will end up with
MARGIN_TARGET_PCT budget at the end of the coming period assuming the same
usage as the previous period. TARGET is set at 50% of period, which is the
previous maximum. This provides smooth convergence for most repetitive IO
patterns.
* Apply donation logic early at 20% budget. There's no risk in doing so as
the calculation is based on the delta between the current budget and the
target budget at the end of the coming period.
* Remove preemptive iocg activation for zero cost IOs. As donation can reach
near zero now, the mere activation doesn't provide any protection anymore.
In the unlikely case that this becomes a problem, the right solution is
assigning appropriate costs for such IOs.
This significantly improves the donation determination logic while also
simplifying it. Now all donations are immediate, exact and smooth.
Signed-off-by: Tejun Heo <tj@kernel.org>
Cc: Andy Newell <newella@fb.com>
Signed-off-by: Jens Axboe <axboe@kernel.dk>
-rw-r--r-- | block/blk-iocost.c | 133 |
1 files changed, 51 insertions, 82 deletions
diff --git a/block/blk-iocost.c b/block/blk-iocost.c index ecc23b827e5d..694f1487208a 100644 --- a/block/blk-iocost.c +++ b/block/blk-iocost.c @@ -217,12 +217,14 @@ enum { MAX_PERIOD = USEC_PER_SEC, /* - * A cgroup's vtime can run 50% behind the device vtime, which + * iocg->vtime is targeted at 50% behind the device vtime, which * serves as its IO credit buffer. Surplus weight adjustment is * immediately canceled if the vtime margin runs below 10%. */ MARGIN_MIN_PCT = 10, - MARGIN_MAX_PCT = 50, + MARGIN_LOW_PCT = 20, + MARGIN_TARGET_PCT = 50, + MARGIN_MAX_PCT = 100, /* Have some play in timer operations */ TIMER_SLACK_PCT = 1, @@ -234,17 +236,6 @@ enum { */ VTIME_VALID_DUR = 300 * USEC_PER_SEC, - /* - * Remember the past three non-zero usages and use the max for - * surplus calculation. Three slots guarantee that we remember one - * full period usage from the last active stretch even after - * partial deactivation and re-activation periods. Don't start - * giving away weight before collecting two data points to prevent - * hweight adjustments based on one partial activation period. - */ - NR_USAGE_SLOTS = 3, - MIN_VALID_USAGES = 2, - /* 1/64k is granular enough and can easily be handled w/ u32 */ WEIGHT_ONE = 1 << 16, @@ -280,14 +271,6 @@ enum { /* don't let cmds which take a very long time pin lagging for too long */ MAX_LAGGING_PERIODS = 10, - /* - * If usage% * 1.25 + 2% is lower than hweight% by more than 3%, - * donate the surplus. - */ - SURPLUS_SCALE_PCT = 125, /* * 125% */ - SURPLUS_SCALE_ABS = WEIGHT_ONE / 50, /* + 2% */ - SURPLUS_MIN_ADJ_DELTA = WEIGHT_ONE / 33, /* 3% */ - /* switch iff the conditions are met for longer than this */ AUTOP_CYCLE_NSEC = 10LLU * NSEC_PER_SEC, @@ -376,6 +359,8 @@ struct ioc_params { struct ioc_margins { s64 min; + s64 low; + s64 target; s64 max; }; @@ -514,11 +499,7 @@ struct ioc_gq { struct iocg_stat desc_stat; struct iocg_stat last_stat; u64 last_stat_abs_vusage; - - /* usage is recorded as fractions of WEIGHT_ONE */ - u32 usage_delta_us; - int usage_idx; - u32 usages[NR_USAGE_SLOTS]; + u64 usage_delta_us; /* this iocg's depth in the hierarchy and ancestors including self */ int level; @@ -737,6 +718,8 @@ static void ioc_refresh_margins(struct ioc *ioc) u64 vrate = atomic64_read(&ioc->vtime_rate); margins->min = (period_us * MARGIN_MIN_PCT / 100) * vrate; + margins->low = (period_us * MARGIN_LOW_PCT / 100) * vrate; + margins->target = (period_us * MARGIN_TARGET_PCT / 100) * vrate; margins->max = (period_us * MARGIN_MAX_PCT / 100) * vrate; } @@ -1228,7 +1211,7 @@ static bool iocg_kick_delay(struct ioc_gq *iocg, struct ioc_now *now) return false; } if (!atomic_read(&blkg->use_delay) && - time_before_eq64(vtime, now->vnow + ioc->margins.max)) + time_before_eq64(vtime, now->vnow + ioc->margins.target)) return false; /* use delay */ @@ -1527,7 +1510,7 @@ static u32 hweight_after_donation(struct ioc_gq *iocg, u32 hwm, u32 usage, { struct ioc *ioc = iocg->ioc; u64 vtime = atomic64_read(&iocg->vtime); - s64 excess; + s64 excess, delta, target, new_hwi; /* see whether minimum margin requirement is met */ if (waitqueue_active(&iocg->waitq) || @@ -1542,15 +1525,28 @@ static u32 hweight_after_donation(struct ioc_gq *iocg, u32 hwm, u32 usage, vtime += excess; } - /* add margin */ - usage = DIV_ROUND_UP(usage * SURPLUS_SCALE_PCT, 100); - usage += SURPLUS_SCALE_ABS; - - /* don't bother if the surplus is too small */ - if (usage + SURPLUS_MIN_ADJ_DELTA > hwm) - return hwm; + /* + * Let's say the distance between iocg's and device's vtimes as a + * fraction of period duration is delta. Assuming that the iocg will + * consume the usage determined above, we want to determine new_hwi so + * that delta equals MARGIN_TARGET at the end of the next period. + * + * We need to execute usage worth of IOs while spending the sum of the + * new budget (1 - MARGIN_TARGET) and the leftover from the last period + * (delta): + * + * usage = (1 - MARGIN_TARGET + delta) * new_hwi + * + * Therefore, the new_hwi is: + * + * new_hwi = usage / (1 - MARGIN_TARGET + delta) + */ + delta = div64_s64(WEIGHT_ONE * (now->vnow - vtime), + now->vnow - ioc->period_at_vtime); + target = WEIGHT_ONE * MARGIN_TARGET_PCT / 100; + new_hwi = div64_s64(WEIGHT_ONE * usage, WEIGHT_ONE - target + delta); - return usage; + return clamp_t(s64, new_hwi, 1, hwm); } /* @@ -1812,7 +1808,7 @@ static void ioc_timer_fn(struct timer_list *timer) u32 ppm_wthr = MILLION - ioc->params.qos[QOS_WPPM]; u32 missed_ppm[2], rq_wait_pct; u64 period_vtime; - int prev_busy_level, i; + int prev_busy_level; /* how were the latencies during the period? */ ioc_lat_stat(ioc, missed_ppm, &rq_wait_pct); @@ -1857,11 +1853,10 @@ static void ioc_timer_fn(struct timer_list *timer) } commit_weights(ioc); - /* calc usages and see whether some weights need to be moved around */ + /* calc usage and see whether some weights need to be moved around */ list_for_each_entry(iocg, &ioc->active_iocgs, active_list) { - u64 vdone, vtime, usage_us; - u32 hw_active, hw_inuse, usage; - int uidx, nr_valid; + u64 vdone, vtime, usage_us, usage_dur; + u32 usage, hw_active, hw_inuse; /* * Collect unused and wind vtime closer to vnow to prevent @@ -1886,15 +1881,11 @@ static void ioc_timer_fn(struct timer_list *timer) nr_lagging++; /* - * Determine absolute usage factoring in pending and in-flight - * IOs to avoid stalls and high-latency completions appearing as - * idle. + * Determine absolute usage factoring in in-flight IOs to avoid + * high-latency completions appearing as idle. */ usage_us = iocg->usage_delta_us; - if (waitqueue_active(&iocg->waitq) && time_before64(vtime, now.vnow)) - usage_us += DIV64_U64_ROUND_UP( - cost_to_abs_cost(now.vnow - vtime, hw_inuse), - now.vrate); + if (vdone != vtime) { u64 inflight_us = DIV64_U64_ROUND_UP( cost_to_abs_cost(vtime - vdone, hw_inuse), @@ -1902,43 +1893,22 @@ static void ioc_timer_fn(struct timer_list *timer) usage_us = max(usage_us, inflight_us); } - /* convert to hweight based usage ratio and record */ - uidx = (iocg->usage_idx + 1) % NR_USAGE_SLOTS; - - if (time_after64(vtime, now.vnow - ioc->margins.min)) { - iocg->usage_idx = uidx; - iocg->usages[uidx] = WEIGHT_ONE; - } else if (usage_us) { - u64 started_at, dur; - - if (time_after64(iocg->activated_at, ioc->period_at)) - started_at = iocg->activated_at; - else - started_at = ioc->period_at; - - dur = max_t(u64, now.now - started_at, 1); + /* convert to hweight based usage ratio */ + if (time_after64(iocg->activated_at, ioc->period_at)) + usage_dur = max_t(u64, now.now - iocg->activated_at, 1); + else + usage_dur = max_t(u64, now.now - ioc->period_at, 1); - iocg->usage_idx = uidx; - iocg->usages[uidx] = clamp_t(u32, - DIV64_U64_ROUND_UP(usage_us * WEIGHT_ONE, dur), + usage = clamp_t(u32, + DIV64_U64_ROUND_UP(usage_us * WEIGHT_ONE, + usage_dur), 1, WEIGHT_ONE); - } - - /* base the decision on max historical usage */ - for (i = 0, usage = 0, nr_valid = 0; i < NR_USAGE_SLOTS; i++) { - if (iocg->usages[i]) { - usage = max(usage, iocg->usages[i]); - nr_valid++; - } - } - if (nr_valid < MIN_VALID_USAGES) - usage = WEIGHT_ONE; /* see whether there's surplus vtime */ WARN_ON_ONCE(!list_empty(&iocg->surplus_list)); if (hw_inuse < hw_active || (!waitqueue_active(&iocg->waitq) && - time_before64(vtime, now.vnow - ioc->margins.max))) { + time_before64(vtime, now.vnow - ioc->margins.low))) { u32 hwa, hwm, new_hwi; /* @@ -2175,15 +2145,14 @@ static void ioc_rqos_throttle(struct rq_qos *rqos, struct bio *bio) if (!ioc->enabled || !iocg->level) return; - /* always activate so that even 0 cost IOs get protected to some level */ - if (!iocg_activate(iocg, &now)) - return; - /* calculate the absolute vtime cost */ abs_cost = calc_vtime_cost(bio, iocg, false); if (!abs_cost) return; + if (!iocg_activate(iocg, &now)) + return; + iocg->cursor = bio_end_sector(bio); vtime = atomic64_read(&iocg->vtime); |