Commit 00d8b035 authored by Heiko Carstens's avatar Heiko Carstens Committed by Vasily Gorbik
Browse files

s390/idle: Slightly optimize idle time accounting 



Slightly optimize account_idle_time_irq() and update_timer_idle():

- Use fast single instruction __atomic64() primitives to update per
  cpu idle_time and idle_count, instead of READ_ONCE() / WRITE_ONCE()
  pairs

- stcctm() is an inline assembly with a full memory barrier. This
  leads to a not necessary extra dereference of smp_cpu_mtid in
  update_timer_idle(). Avoid this and read smp_cpu_mtid into a
  variable

- Use __this_cpu_add() instead of this_cpu_add() to avoid disabling /
  enabling of preemption several times in a loop in update_timer_idle().

Reviewed-by: default avatarSven Schnelle <svens@linux.ibm.com>
Signed-off-by: default avatarHeiko Carstens <hca@linux.ibm.com>
Signed-off-by: default avatarVasily Gorbik <gor@linux.ibm.com>
parent aefa6ec8

arch/s390/kernel/idle.c

+8 −7
Original line number Diff line number Diff line
@@ -26,12 +26,13 @@ void update_timer_idle(void) 
	struct s390_idle_data *idle = this_cpu_ptr(&s390_idle);

	struct lowcore *lc = get_lowcore();

	u64 cycles_new[8];

	int i;

	int i, mtid;



	if (smp_cpu_mtid) {

		stcctm(MT_DIAG, smp_cpu_mtid, cycles_new);

		for (i = 0; i < smp_cpu_mtid; i++)

			this_cpu_add(mt_cycles[i], cycles_new[i] - idle->mt_cycles_enter[i]);

	mtid = smp_cpu_mtid;

	if (mtid) {

		stcctm(MT_DIAG, mtid, cycles_new);

		for (i = 0; i < mtid; i++)

			__this_cpu_add(mt_cycles[i], cycles_new[i] - idle->mt_cycles_enter[i]);

	}



	/*
@@ -58,8 +59,8 @@ void account_idle_time_irq(void) 
	idle_time = get_lowcore()->int_clock - idle->clock_idle_enter;



	/* Account time spent with enabled wait psw loaded as idle time. */

	WRITE_ONCE(idle->idle_time, READ_ONCE(idle->idle_time) + idle_time);

	WRITE_ONCE(idle->idle_count, READ_ONCE(idle->idle_count) + 1);

	__atomic64_add(idle_time, &idle->idle_time);

	__atomic64_add_const(1, &idle->idle_count);

	account_idle_time(cputime_to_nsecs(idle_time));

}