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sched/fair: Add lsub_positive() and use it consistently

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The following pattern:

   var -= min_t(typeof(var), var, val);

is used multiple times in fair.c.

The existing sub_positive() already captures that pattern, but it also
adds an explicit load-store to properly support lockless observations.
In other cases the pattern above is used to update local, and/or not
concurrently accessed, variables.

Let's add a simpler version of sub_positive(), targeted at local variables
updates, which gives the same readability benefits at calling sites,
without enforcing {READ,WRITE}_ONCE() barriers.

Signed-off-by: Patrick Bellasi <patrick.bellasi@arm.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Cc: Dietmar Eggemann <dietmar.eggemann@arm.com>
Cc: Juri Lelli <juri.lelli@redhat.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Morten Rasmussen <morten.rasmussen@arm.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Quentin Perret <quentin.perret@arm.com>
Cc: Steve Muckle <smuckle@google.com>
Cc: Suren Baghdasaryan <surenb@google.com>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Todd Kjos <tkjos@google.com>
Cc: Vincent Guittot <vincent.guittot@linaro.org>
Link: https://lore.kernel.org/lkml/20181031184527.GA3178@hirez.programming.kicks-ass.net
Signed-off-by: Ingo Molnar <mingo@kernel.org>
This commit is contained in:
Patrick Bellasi 2018-11-05 14:54:00 +00:00 committed by Ingo Molnar
parent 92a801e5d5
commit b5c0ce7bd1
1 changed files with 17 additions and 7 deletions
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24
kernel/sched/fair.c
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@ -2734,6 +2734,17 @@ account_entity_dequeue(struct cfs_rq *cfs_rq, struct sched_entity *se)
WRITE_ONCE(*ptr, res); \
} while (0)
/*
* Remove and clamp on negative, from a local variable.
*
* A variant of sub_positive(), which does not use explicit load-store
* and is thus optimized for local variable updates.
*/
#define lsub_positive(_ptr, _val) do { \
typeof(_ptr) ptr = (_ptr); \
*ptr -= min_t(typeof(*ptr), *ptr, _val); \
} while (0)
#ifdef CONFIG_SMP
static inline void
enqueue_runnable_load_avg(struct cfs_rq *cfs_rq, struct sched_entity *se)
@ -4639,7 +4650,7 @@ static int do_sched_cfs_period_timer(struct cfs_bandwidth *cfs_b, int overrun)
cfs_b->distribute_running = 0;
throttled = !list_empty(&cfs_b->throttled_cfs_rq);
cfs_b->runtime -= min(runtime, cfs_b->runtime);
lsub_positive(&cfs_b->runtime, runtime);
}
/*
@ -4773,7 +4784,7 @@ static void do_sched_cfs_slack_timer(struct cfs_bandwidth *cfs_b)
raw_spin_lock(&cfs_b->lock);
if (expires == cfs_b->runtime_expires)
cfs_b->runtime -= min(runtime, cfs_b->runtime);
lsub_positive(&cfs_b->runtime, runtime);
cfs_b->distribute_running = 0;
raw_spin_unlock(&cfs_b->lock);
}
@ -6240,7 +6251,7 @@ static unsigned long cpu_util_without(int cpu, struct task_struct *p)
util = READ_ONCE(cfs_rq->avg.util_avg);
/* Discount task's util from CPU's util */
util -= min_t(unsigned int, util, task_util(p));
lsub_positive(&util, task_util(p));
/*
* Covered cases:
@ -6289,10 +6300,9 @@ static unsigned long cpu_util_without(int cpu, struct task_struct *p)
* properly fix the execl regression and it helps in further
* reducing the chances for the above race.
*/
if (unlikely(task_on_rq_queued(p) || current == p)) {
estimated -= min_t(unsigned int, estimated,
_task_util_est(p));
}
if (unlikely(task_on_rq_queued(p) || current == p))
lsub_positive(&estimated, _task_util_est(p));
util = max(util, estimated);
}