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Message-Id: <20200901185257.645114-12-tj@kernel.org>
Date: Tue, 1 Sep 2020 14:52:41 -0400
From: Tejun Heo <tj@...nel.org>
To: axboe@...nel.dk
Cc: linux-block@...r.kernel.org, cgroups@...r.kernel.org,
linux-kernel@...r.kernel.org, kernel-team@...com, newella@...com,
Tejun Heo <tj@...nel.org>
Subject: [PATCH 11/27] blk-iocost: streamline vtime margin and timer slack handling
The margin handling was pretty inconsistent.
* ioc->margin_us and ioc->inuse_margin_vtime were used as vtime margin
thresholds. However, the two are in different units with the former
requiring conversion to vtime on use.
* iocg_kick_waitq() was using a quarter of WAITQ_TIMER_MARGIN_PCT of
period_us as the timer slack - ~1.2%. While iocg_kick_delay() was using a
quarter of ioc->margin_us - ~12.5%. There aren't strong reasons to use
different values for the two.
This patch cleans up margin and timer slack handling:
* vtime margins are now recorded in ioc->margins.{min, max} on period
duration changes and used consistently.
* Timer slack is now 1% of period_us and recorded in ioc->timer_slack_ns and
used consistently for iocg_kick_waitq() and iocg_kick_delay().
The only functional change is shortening of timer slack. No meaningful
visible change is expected.
Signed-off-by: Tejun Heo <tj@...nel.org>
---
block/blk-iocost.c | 67 ++++++++++++++++++++++++++--------------------
1 file changed, 38 insertions(+), 29 deletions(-)
diff --git a/block/blk-iocost.c b/block/blk-iocost.c
index dc72cd965837..f36988657594 100644
--- a/block/blk-iocost.c
+++ b/block/blk-iocost.c
@@ -221,11 +221,11 @@ enum {
* serves as its IO credit buffer. Surplus weight adjustment is
* immediately canceled if the vtime margin runs below 10%.
*/
- MARGIN_PCT = 50,
- INUSE_MARGIN_PCT = 10,
+ MARGIN_MIN_PCT = 10,
+ MARGIN_MAX_PCT = 50,
- /* Have some play in waitq timer operations */
- WAITQ_TIMER_MARGIN_PCT = 5,
+ /* Have some play in timer operations */
+ TIMER_SLACK_PCT = 1,
/*
* vtime can wrap well within a reasonable uptime when vrate is
@@ -374,6 +374,11 @@ struct ioc_params {
u32 too_slow_vrate_pct;
};
+struct ioc_margins {
+ s64 min;
+ s64 max;
+};
+
struct ioc_missed {
local_t nr_met;
local_t nr_missed;
@@ -395,8 +400,9 @@ struct ioc {
bool enabled;
struct ioc_params params;
+ struct ioc_margins margins;
u32 period_us;
- u32 margin_us;
+ u32 timer_slack_ns;
u64 vrate_min;
u64 vrate_max;
@@ -415,7 +421,6 @@ struct ioc {
atomic64_t cur_period; /* inc'd each period */
int busy_level; /* saturation history */
- u64 inuse_margin_vtime;
bool weights_updated;
atomic_t hweight_gen; /* for lazy hweights */
@@ -678,6 +683,16 @@ static void iocg_commit_bio(struct ioc_gq *iocg, struct bio *bio, u64 cost)
#define CREATE_TRACE_POINTS
#include <trace/events/iocost.h>
+static void ioc_refresh_margins(struct ioc *ioc)
+{
+ struct ioc_margins *margins = &ioc->margins;
+ u32 period_us = ioc->period_us;
+ u64 vrate = atomic64_read(&ioc->vtime_rate);
+
+ margins->min = (period_us * MARGIN_MIN_PCT / 100) * vrate;
+ margins->max = (period_us * MARGIN_MAX_PCT / 100) * vrate;
+}
+
/* latency Qos params changed, update period_us and all the dependent params */
static void ioc_refresh_period_us(struct ioc *ioc)
{
@@ -711,9 +726,10 @@ static void ioc_refresh_period_us(struct ioc *ioc)
/* calculate dependent params */
ioc->period_us = period_us;
- ioc->margin_us = period_us * MARGIN_PCT / 100;
- ioc->inuse_margin_vtime = DIV64_U64_ROUND_UP(
- period_us * VTIME_PER_USEC * INUSE_MARGIN_PCT, 100);
+ ioc->timer_slack_ns = div64_u64(
+ (u64)period_us * NSEC_PER_USEC * TIMER_SLACK_PCT,
+ 100);
+ ioc_refresh_margins(ioc);
}
static int ioc_autop_idx(struct ioc *ioc)
@@ -1031,7 +1047,7 @@ static bool iocg_activate(struct ioc_gq *iocg, struct ioc_now *now)
{
struct ioc *ioc = iocg->ioc;
u64 last_period, cur_period, max_period_delta;
- u64 vtime, vmargin, vmin;
+ u64 vtime, vmin;
int i;
/*
@@ -1077,8 +1093,7 @@ static bool iocg_activate(struct ioc_gq *iocg, struct ioc_now *now)
*/
max_period_delta = DIV64_U64_ROUND_UP(VTIME_VALID_DUR, ioc->period_us);
vtime = atomic64_read(&iocg->vtime);
- vmargin = ioc->margin_us * now->vrate;
- vmin = now->vnow - vmargin;
+ vmin = now->vnow - ioc->margins.max;
if (last_period + max_period_delta < cur_period ||
time_before64(vtime, vmin)) {
@@ -1121,8 +1136,6 @@ static bool iocg_kick_delay(struct ioc_gq *iocg, struct ioc_now *now)
struct ioc *ioc = iocg->ioc;
struct blkcg_gq *blkg = iocg_to_blkg(iocg);
u64 vtime = atomic64_read(&iocg->vtime);
- u64 vmargin = ioc->margin_us * now->vrate;
- u64 margin_ns = ioc->margin_us * NSEC_PER_USEC;
u64 delta_ns, expires, oexpires;
u32 hw_inuse;
@@ -1142,7 +1155,7 @@ 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 + vmargin))
+ time_before_eq64(vtime, now->vnow + ioc->margins.max))
return false;
/* use delay */
@@ -1154,11 +1167,11 @@ static bool iocg_kick_delay(struct ioc_gq *iocg, struct ioc_now *now)
/* if already active and close enough, don't bother */
oexpires = ktime_to_ns(hrtimer_get_softexpires(&iocg->delay_timer));
if (hrtimer_is_queued(&iocg->delay_timer) &&
- abs(oexpires - expires) <= margin_ns / 4)
+ abs(oexpires - expires) <= ioc->timer_slack_ns)
return true;
hrtimer_start_range_ns(&iocg->delay_timer, ns_to_ktime(expires),
- margin_ns / 4, HRTIMER_MODE_ABS);
+ ioc->timer_slack_ns, HRTIMER_MODE_ABS);
return true;
}
@@ -1206,8 +1219,6 @@ static void iocg_kick_waitq(struct ioc_gq *iocg, struct ioc_now *now)
{
struct ioc *ioc = iocg->ioc;
struct iocg_wake_ctx ctx = { .iocg = iocg };
- u64 margin_ns = (u64)(ioc->period_us *
- WAITQ_TIMER_MARGIN_PCT / 100) * NSEC_PER_USEC;
u64 vdebt, vshortage, expires, oexpires;
s64 vbudget;
u32 hw_inuse;
@@ -1243,20 +1254,20 @@ static void iocg_kick_waitq(struct ioc_gq *iocg, struct ioc_now *now)
if (WARN_ON_ONCE(ctx.vbudget >= 0))
return;
- /* determine next wakeup, add a quarter margin to guarantee chunking */
+ /* determine next wakeup, add a timer margin to guarantee chunking */
vshortage = -ctx.vbudget;
expires = now->now_ns +
DIV64_U64_ROUND_UP(vshortage, now->vrate) * NSEC_PER_USEC;
- expires += margin_ns / 4;
+ expires += ioc->timer_slack_ns;
/* if already active and close enough, don't bother */
oexpires = ktime_to_ns(hrtimer_get_softexpires(&iocg->waitq_timer));
if (hrtimer_is_queued(&iocg->waitq_timer) &&
- abs(oexpires - expires) <= margin_ns / 4)
+ abs(oexpires - expires) <= ioc->timer_slack_ns)
return;
hrtimer_start_range_ns(&iocg->waitq_timer, ns_to_ktime(expires),
- margin_ns / 4, HRTIMER_MODE_ABS);
+ ioc->timer_slack_ns, HRTIMER_MODE_ABS);
}
static enum hrtimer_restart iocg_waitq_timer_fn(struct hrtimer *timer)
@@ -1399,7 +1410,7 @@ static void ioc_timer_fn(struct timer_list *timer)
/* calc usages and see whether some weights need to be moved around */
list_for_each_entry(iocg, &ioc->active_iocgs, active_list) {
- u64 vdone, vtime, vusage, vmargin, vmin;
+ u64 vdone, vtime, vusage, vmin;
u32 hw_active, hw_inuse, usage;
/*
@@ -1450,8 +1461,7 @@ static void ioc_timer_fn(struct timer_list *timer)
}
/* see whether there's surplus vtime */
- vmargin = ioc->margin_us * now.vrate;
- vmin = now.vnow - vmargin;
+ vmin = now.vnow - ioc->margins.max;
iocg->has_surplus = false;
@@ -1623,8 +1633,7 @@ static void ioc_timer_fn(struct timer_list *timer)
nr_surpluses);
atomic64_set(&ioc->vtime_rate, vrate);
- ioc->inuse_margin_vtime = DIV64_U64_ROUND_UP(
- ioc->period_us * vrate * INUSE_MARGIN_PCT, 100);
+ ioc_refresh_margins(ioc);
} else if (ioc->busy_level != prev_busy_level || nr_lagging) {
trace_iocost_ioc_vrate_adj(ioc, atomic64_read(&ioc->vtime_rate),
missed_ppm, rq_wait_pct, nr_lagging,
@@ -1754,7 +1763,7 @@ static void ioc_rqos_throttle(struct rq_qos *rqos, struct bio *bio)
current_hweight(iocg, &hw_active, &hw_inuse);
if (hw_inuse < hw_active &&
- time_after_eq64(vtime + ioc->inuse_margin_vtime, now.vnow)) {
+ time_after_eq64(vtime + ioc->margins.min, now.vnow)) {
TRACE_IOCG_PATH(inuse_reset, iocg, &now,
iocg->inuse, iocg->weight, hw_inuse, hw_active);
spin_lock_irq(&ioc->lock);
--
2.26.2
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