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Misc fixes:

Browse Source 
- Fix performance regression caused by lack of intended
    batching of RCU callbacks by over-eager NOHZ-full code.
 
  - Fix cgroups related corruption of load_avg and load_sum metrics.
 
  - Three fixes to fix blocked load, util_sum/runnable_sum and
    util_est tracking bugs.
 
 Signed-off-by: Ingo Molnar <mingo@kernel.org>
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Merge tag 'sched-urgent-2021-06-12' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip

Pull scheduler fixes from Ingo Molnar:
 "Misc fixes:

   - Fix performance regression caused by lack of intended batching of
     RCU callbacks by over-eager NOHZ-full code.

   - Fix cgroups related corruption of load_avg and load_sum metrics.

   - Three fixes to fix blocked load, util_sum/runnable_sum and util_est
     tracking bugs"

* tag 'sched-urgent-2021-06-12' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip:
  sched/fair: Fix util_est UTIL_AVG_UNCHANGED handling
  sched/pelt: Ensure that *_sum is always synced with *_avg
  tick/nohz: Only check for RCU deferred wakeup on user/guest entry when needed
  sched/fair: Make sure to update tg contrib for blocked load
  sched/fair: Keep load_avg and load_sum synced
This commit is contained in:
Linus Torvalds 2021-06-12 11:41:28 -07:00
commit 99f925947a
8 changed files with 41 additions and 25 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

3
include/linux/entry-kvm.h
View File

@ -3,6 +3,7 @@
#define __LINUX_ENTRYKVM_H
#include <linux/entry-common.h>
#include <linux/tick.h>
/* Transfer to guest mode work */
#ifdef CONFIG_KVM_XFER_TO_GUEST_WORK
@ -57,7 +58,7 @@ int xfer_to_guest_mode_handle_work(struct kvm_vcpu *vcpu);
static inline void xfer_to_guest_mode_prepare(void)
{
lockdep_assert_irqs_disabled();
rcu_nocb_flush_deferred_wakeup();
tick_nohz_user_enter_prepare();
}
/**

8
include/linux/sched.h
View File

@ -350,11 +350,19 @@ struct load_weight {
* Only for tasks we track a moving average of the past instantaneous
* estimated utilization. This allows to absorb sporadic drops in utilization
* of an otherwise almost periodic task.
*
* The UTIL_AVG_UNCHANGED flag is used to synchronize util_est with util_avg
* updates. When a task is dequeued, its util_est should not be updated if its
* util_avg has not been updated in the meantime.
* This information is mapped into the MSB bit of util_est.enqueued at dequeue
* time. Since max value of util_est.enqueued for a task is 1024 (PELT util_avg
* for a task) it is safe to use MSB.
*/
struct util_est {
unsigned int enqueued;
unsigned int ewma;
#define UTIL_EST_WEIGHT_SHIFT 2
#define UTIL_AVG_UNCHANGED 0x80000000
} __attribute__((__aligned__(sizeof(u64))));
/*

7
include/linux/tick.h
View File

@ -11,6 +11,7 @@
#include <linux/context_tracking_state.h>
#include <linux/cpumask.h>
#include <linux/sched.h>
#include <linux/rcupdate.h>
#ifdef CONFIG_GENERIC_CLOCKEVENTS
extern void __init tick_init(void);
@ -300,4 +301,10 @@ static inline void tick_nohz_task_switch(void)
__tick_nohz_task_switch();
}
static inline void tick_nohz_user_enter_prepare(void)
{
if (tick_nohz_full_cpu(smp_processor_id()))
rcu_nocb_flush_deferred_wakeup();
}
#endif

5
kernel/entry/common.c
View File

@ -5,6 +5,7 @@
#include <linux/highmem.h>
#include <linux/livepatch.h>
#include <linux/audit.h>
#include <linux/tick.h>
#include "common.h"
@ -186,7 +187,7 @@ static unsigned long exit_to_user_mode_loop(struct pt_regs *regs,
local_irq_disable_exit_to_user();
/* Check if any of the above work has queued a deferred wakeup */
rcu_nocb_flush_deferred_wakeup();
tick_nohz_user_enter_prepare();
ti_work = READ_ONCE(current_thread_info()->flags);
}
@ -202,7 +203,7 @@ static void exit_to_user_mode_prepare(struct pt_regs *regs)
lockdep_assert_irqs_disabled();
/* Flush pending rcuog wakeup before the last need_resched() check */
rcu_nocb_flush_deferred_wakeup();
tick_nohz_user_enter_prepare();
if (unlikely(ti_work & EXIT_TO_USER_MODE_WORK))
ti_work = exit_to_user_mode_loop(regs, ti_work);

3
kernel/sched/debug.c
View File

@ -885,6 +885,7 @@ static const struct seq_operations sched_debug_sops = {
#define __PS(S, F) SEQ_printf(m, "%-45s:%21Ld\n", S, (long long)(F))
#define __P(F) __PS(#F, F)
#define P(F) __PS(#F, p->F)
#define PM(F, M) __PS(#F, p->F & (M))
#define __PSN(S, F) SEQ_printf(m, "%-45s:%14Ld.%06ld\n", S, SPLIT_NS((long long)(F)))
#define __PN(F) __PSN(#F, F)
#define PN(F) __PSN(#F, p->F)
@ -1011,7 +1012,7 @@ void proc_sched_show_task(struct task_struct *p, struct pid_namespace *ns,
P(se.avg.util_avg);
P(se.avg.last_update_time);
P(se.avg.util_est.ewma);
P(se.avg.util_est.enqueued);
PM(se.avg.util_est.enqueued, ~UTIL_AVG_UNCHANGED);
#endif
#ifdef CONFIG_UCLAMP_TASK
__PS("uclamp.min", p->uclamp_req[UCLAMP_MIN].value);

28
kernel/sched/fair.c
View File

@ -3499,10 +3499,9 @@ update_tg_cfs_runnable(struct cfs_rq *cfs_rq, struct sched_entity *se, struct cf
static inline void
update_tg_cfs_load(struct cfs_rq *cfs_rq, struct sched_entity *se, struct cfs_rq *gcfs_rq)
{
long delta_avg, running_sum, runnable_sum = gcfs_rq->prop_runnable_sum;
long delta, running_sum, runnable_sum = gcfs_rq->prop_runnable_sum;
unsigned long load_avg;
u64 load_sum = 0;
s64 delta_sum;
u32 divider;
if (!runnable_sum)
@ -3549,13 +3548,13 @@ update_tg_cfs_load(struct cfs_rq *cfs_rq, struct sched_entity *se, struct cfs_rq
load_sum = (s64)se_weight(se) * runnable_sum;
load_avg = div_s64(load_sum, divider);
delta_sum = load_sum - (s64)se_weight(se) * se->avg.load_sum;
delta_avg = load_avg - se->avg.load_avg;
delta = load_avg - se->avg.load_avg;
se->avg.load_sum = runnable_sum;
se->avg.load_avg = load_avg;
add_positive(&cfs_rq->avg.load_avg, delta_avg);
add_positive(&cfs_rq->avg.load_sum, delta_sum);
add_positive(&cfs_rq->avg.load_avg, delta);
cfs_rq->avg.load_sum = cfs_rq->avg.load_avg * divider;
}
static inline void add_tg_cfs_propagate(struct cfs_rq *cfs_rq, long runnable_sum)
@ -3766,11 +3765,17 @@ static void attach_entity_load_avg(struct cfs_rq *cfs_rq, struct sched_entity *s
*/
static void detach_entity_load_avg(struct cfs_rq *cfs_rq, struct sched_entity *se)
{
/*
* cfs_rq->avg.period_contrib can be used for both cfs_rq and se.
* See ___update_load_avg() for details.
*/
u32 divider = get_pelt_divider(&cfs_rq->avg);
dequeue_load_avg(cfs_rq, se);
sub_positive(&cfs_rq->avg.util_avg, se->avg.util_avg);
sub_positive(&cfs_rq->avg.util_sum, se->avg.util_sum);
cfs_rq->avg.util_sum = cfs_rq->avg.util_avg * divider;
sub_positive(&cfs_rq->avg.runnable_avg, se->avg.runnable_avg);
sub_positive(&cfs_rq->avg.runnable_sum, se->avg.runnable_sum);
cfs_rq->avg.runnable_sum = cfs_rq->avg.runnable_avg * divider;
add_tg_cfs_propagate(cfs_rq, -se->avg.load_sum);
@ -3902,7 +3907,7 @@ static inline unsigned long _task_util_est(struct task_struct *p)
{
struct util_est ue = READ_ONCE(p->se.avg.util_est);
return (max(ue.ewma, ue.enqueued) | UTIL_AVG_UNCHANGED);
return max(ue.ewma, (ue.enqueued & ~UTIL_AVG_UNCHANGED));
}
static inline unsigned long task_util_est(struct task_struct *p)
@ -4002,7 +4007,7 @@ static inline void util_est_update(struct cfs_rq *cfs_rq,
* Reset EWMA on utilization increases, the moving average is used only
* to smooth utilization decreases.
*/
ue.enqueued = (task_util(p) | UTIL_AVG_UNCHANGED);
ue.enqueued = task_util(p);
if (sched_feat(UTIL_EST_FASTUP)) {
if (ue.ewma < ue.enqueued) {
ue.ewma = ue.enqueued;
@ -4051,6 +4056,7 @@ static inline void util_est_update(struct cfs_rq *cfs_rq,
ue.ewma += last_ewma_diff;
ue.ewma >>= UTIL_EST_WEIGHT_SHIFT;
done:
ue.enqueued |= UTIL_AVG_UNCHANGED;
WRITE_ONCE(p->se.avg.util_est, ue);
trace_sched_util_est_se_tp(&p->se);
@ -8030,7 +8036,7 @@ static bool __update_blocked_fair(struct rq *rq, bool *done)
/* Propagate pending load changes to the parent, if any: */
se = cfs_rq->tg->se[cpu];
if (se && !skip_blocked_update(se))
update_load_avg(cfs_rq_of(se), se, 0);
update_load_avg(cfs_rq_of(se), se, UPDATE_TG);
/*
* There can be a lot of idle CPU cgroups. Don't let fully

11
kernel/sched/pelt.h
View File

@ -42,15 +42,6 @@ static inline u32 get_pelt_divider(struct sched_avg *avg)
return LOAD_AVG_MAX - 1024 + avg->period_contrib;
}
/*
* When a task is dequeued, its estimated utilization should not be update if
* its util_avg has not been updated at least once.
* This flag is used to synchronize util_avg updates with util_est updates.
* We map this information into the LSB bit of the utilization saved at
* dequeue time (i.e. util_est.dequeued).
*/
#define UTIL_AVG_UNCHANGED 0x1
static inline void cfs_se_util_change(struct sched_avg *avg)
{
unsigned int enqueued;
@ -58,7 +49,7 @@ static inline void cfs_se_util_change(struct sched_avg *avg)
if (!sched_feat(UTIL_EST))
return;
/* Avoid store if the flag has been already set */
/* Avoid store if the flag has been already reset */
enqueued = avg->util_est.enqueued;
if (!(enqueued & UTIL_AVG_UNCHANGED))
return;

1
kernel/time/tick-sched.c
View File

@ -230,6 +230,7 @@ static void tick_sched_handle(struct tick_sched *ts, struct pt_regs *regs)
#ifdef CONFIG_NO_HZ_FULL
cpumask_var_t tick_nohz_full_mask;
EXPORT_SYMBOL_GPL(tick_nohz_full_mask);
bool tick_nohz_full_running;
EXPORT_SYMBOL_GPL(tick_nohz_full_running);
static atomic_t tick_dep_mask;