linux-kernel - [PATCH v4] time/tick-sched: idle load balancing when nohz

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Date: Thu,  9 May 2024 10:29:32 +0100
From: Levi Yun <ppbuk5246@...il.com>
To: anna-maria@...utronix.de,
	frederic@...nel.org,
	mingo@...nel.org,
	tglx@...utronix.de,
	Markus.Elfring@....de
Cc: linux-kernel@...r.kernel.org,
	Levi Yun <ppbuk5246@...il.com>
Subject: [PATCH v4] time/tick-sched: idle load balancing when nohz_full cpu becomes idle.

When nohz_full CPU stops tick in tick_nohz_irq_exit(),
It wouldn't be chosen to perform idle load balancing because it doesn't
call nohz_balance_enter_idle() in tick_nohz_idle_stop_tick() when it
becomes idle.

Formerly, __tick_nohz_idle_enter() is called in both
tick_nohz_irq_exit() and in do_idle().
That's why commit a0db971e4eb6 ("nohz: Move idle balancer registration
to the idle path") prevents nohz_full cpu which isn't yet
idle state but tick is stopped from entering idle balance.

However, this prevents nohz_full cpu which already stops tick from
entering idle balacne when this cpu really becomes idle state.

Currently, tick_nohz_idle_stop_tick() is only called in idle state and
it calls nohz_balance_enter_idle(). this function tracks the CPU
which is part of nohz.idle_cpus_mask with rq->nohz_tick_stopped properly.

Therefore, Change tick_nohz_idle_stop_tick() to call nohz_balance_enter_idle()
without checking !was_stopped so that nohz_full cpu can be chosen to
perform idle load balancing when it enters idle state.

Fixes: a0db971e4eb6 ("nohz: Move idle balancer registration to the idle path")
Signed-off-by: Levi Yun <ppbuk5246@...il.com>
---
v4:
	- Add fixes tags.

v3:
	- Rewording commit message.

v2:
	- Fix typos in commit message.

 kernel/time/tick-sched.c | 6 ++++--
 1 file changed, 4 insertions(+), 2 deletions(-)

diff --git a/kernel/time/tick-sched.c b/kernel/time/tick-sched.c
index 71a792cd8936..31a4cd89782f 100644
--- a/kernel/time/tick-sched.c
+++ b/kernel/time/tick-sched.c
@@ -1228,8 +1228,10 @@ void tick_nohz_idle_stop_tick(void)
 		ts->idle_sleeps++;
 		ts->idle_expires = expires;

-		if (!was_stopped && tick_sched_flag_test(ts, TS_FLAG_STOPPED)) {
-			ts->idle_jiffies = ts->last_jiffies;
+		if (tick_sched_flag_test(ts, TS_FLAG_STOPPED)) {
+			if (!was_stopped)
+				ts->idle_jiffies = ts->last_jiffies;
+
 			nohz_balance_enter_idle(cpu);
 		}
 	} else {
--
2.41.0