[PATCH 5.5 028/176] timers/nohz: Update NOHZ load in remote tick

Greg Kroah-Hartman
2020-03-03T17:45:33Z

From: Peter Zijlstra (Intel) <peterz@infradead.org>

[ Upstream commit ebc0f83c78a2d26384401ecf2d2fa48063c0ee27 ]

The way loadavg is tracked during nohz only pays attention to the load
upon entering nohz. This can be particularly noticeable if full nohz is
entered while non-idle, and then the cpu goes idle and stays that way for
a long time.

Use the remote tick to ensure that full nohz cpus report their deltas
within a reasonable time.

[ swood: Added changelog and removed recheck of stopped tick. ]

Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Signed-off-by: Scott Wood <swood@redhat.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Link: https://lkml.kernel.org/r/1578736419-14628-3-git-send-email-swood@redhat.com
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
include/linux/sched/nohz.h | 2 ++
kernel/sched/core.c | 4 +++-
kernel/sched/loadavg.c | 33 +++++++++++++++++++++++----------
3 files changed, 28 insertions(+), 11 deletions(-)

diff --git a/include/linux/sched/nohz.h b/include/linux/sched/nohz.h
index 1abe91ff6e4a2..6d67e9a5af6bb 100644
--- a/include/linux/sched/nohz.h
+++ b/include/linux/sched/nohz.h
@@ -15,9 +15,11 @@ static inline void nohz_balance_enter_idle(int cpu) { }

#ifdef CONFIG_NO_HZ_COMMON
void calc_load_nohz_start(void);
+void calc_load_nohz_remote(struct rq *rq);
void calc_load_nohz_stop(void);
#else
static inline void calc_load_nohz_start(void) { }
+static inline void calc_load_nohz_remote(struct rq *rq) { }
static inline void calc_load_nohz_stop(void) { }
#endif /* CONFIG_NO_HZ_COMMON */

diff --git a/kernel/sched/core.c b/kernel/sched/core.c
index 3cb879f4eb9c6..65ed821335dd5 100644
--- a/kernel/sched/core.c
+++ b/kernel/sched/core.c
@@ -3677,6 +3677,7 @@ static void sched_tick_remote(struct work_struct *work)
if (cpu_is_offline(cpu))
goto out_unlock;

+ curr = rq->curr;
update_rq_clock(rq);

if (!is_idle_task(curr)) {
@@ -3689,10 +3690,11 @@ static void sched_tick_remote(struct work_struct *work)
}
curr->sched_class->task_tick(rq, curr, 0);

+ calc_load_nohz_remote(rq);
out_unlock:
rq_unlock_irq(rq, &rf);
-
out_requeue:
+
/*
* Run the remote tick once per second (1Hz). This arbitrary
* frequency is large enough to avoid overload but short enough
diff --git a/kernel/sched/loadavg.c b/kernel/sched/loadavg.c
index 28a516575c181..de22da666ac73 100644
--- a/kernel/sched/loadavg.c
+++ b/kernel/sched/loadavg.c
@@ -231,16 +231,11 @@ static inline int calc_load_read_idx(void)
return calc_load_idx & 1;
}

-void calc_load_nohz_start(void)
+static void calc_load_nohz_fold(struct rq *rq)
{
- struct rq *this_rq = this_rq();
long delta;

- /*
- * We're going into NO_HZ mode, if there's any pending delta, fold it
- * into the pending NO_HZ delta.
- */
- delta = calc_load_fold_active(this_rq, 0);
+ delta = calc_load_fold_active(rq, 0);
if (delta) {
int idx = calc_load_write_idx();

@@ -248,6 +243,24 @@ void calc_load_nohz_start(void)
}
}

+void calc_load_nohz_start(void)
+{
+ /*
+ * We're going into NO_HZ mode, if there's any pending delta, fold it
+ * into the pending NO_HZ delta.
+ */
+ calc_load_nohz_fold(this_rq());
+}
+
+/*
+ * Keep track of the load for NOHZ_FULL, must be called between
+ * calc_load_nohz_{start,stop}().
+ */
+void calc_load_nohz_remote(struct rq *rq)
+{
+ calc_load_nohz_fold(rq);
+}
+
void calc_load_nohz_stop(void)
{
struct rq *this_rq = this_rq();
@@ -268,7 +281,7 @@ void calc_load_nohz_stop(void)
this_rq->calc_load_update += LOAD_FREQ;
}

-static long calc_load_nohz_fold(void)
+static long calc_load_nohz_read(void)
{
int idx = calc_load_read_idx();
long delta = 0;
@@ -323,7 +336,7 @@ static void calc_global_nohz(void)
}
#else /* !CONFIG_NO_HZ_COMMON */

-static inline long calc_load_nohz_fold(void) { return 0; }
+static inline long calc_load_nohz_read(void) { return 0; }
static inline void calc_global_nohz(void) { }

#endif /* CONFIG_NO_HZ_COMMON */
@@ -346,7 +359,7 @@ void calc_global_load(unsigned long ticks)
/*
* Fold the 'old' NO_HZ-delta to include all NO_HZ CPUs.
*/
- delta = calc_load_nohz_fold();
+ delta = calc_load_nohz_read();
if (delta)
atomic_long_add(delta, &calc_load_tasks);

--
2.20.1