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Commit 3c5d92a0 authored by Martin Schwidefsky's avatar Martin Schwidefsky Committed by Thomas Gleixner
Browse files

nohz: Introduce arch_needs_cpu 



Allow the architecture to request a normal jiffy tick when the system
goes idle and tick_nohz_stop_sched_tick is called . On s390 the hook is
used to prevent the system going fully idle if there has been an
interrupt other than a clock comparator interrupt since the last wakeup.

On s390 the HiperSockets response time for 1 connection ping-pong goes
down from 42 to 34 microseconds. The CPU cost decreases by 27%.

Signed-off-by: default avatarMartin Schwidefsky <schwidefsky@de.ibm.com>
LKML-Reference: <20090929122533.402715150@de.ibm.com>
Signed-off-by: default avatarThomas Gleixner <tglx@linutronix.de>
parent eed3b9cf

arch/s390/include/asm/cputime.h

+8 −0
Original line number Diff line number Diff line
@@ -183,6 +183,7 @@ struct s390_idle_data { 
	unsigned long long idle_count;

	unsigned long long idle_enter;

	unsigned long long idle_time;

	int nohz_delay;

};



DECLARE_PER_CPU(struct s390_idle_data, s390_idle);
@@ -198,4 +199,11 @@ static inline void s390_idle_check(void) 
		vtime_start_cpu();

}



static inline int s390_nohz_delay(int cpu)

{

	return per_cpu(s390_idle, cpu).nohz_delay != 0;

}



#define arch_needs_cpu(cpu) s390_nohz_delay(cpu)



#endif /* _S390_CPUTIME_H */

arch/s390/kernel/s390_ext.c

+2 −0
Original line number Diff line number Diff line
@@ -126,6 +126,8 @@ void __irq_entry do_extint(struct pt_regs *regs, unsigned short code) 
		/* Serve timer interrupts first. */

		clock_comparator_work();

	kstat_cpu(smp_processor_id()).irqs[EXTERNAL_INTERRUPT]++;

	if (code != 0x1004)

		__get_cpu_var(s390_idle).nohz_delay = 1;

        index = ext_hash(code);

	for (p = ext_int_hash[index]; p; p = p->next) {

		if (likely(p->code == code))

arch/s390/kernel/vtime.c

+2 −0
Original line number Diff line number Diff line
@@ -167,6 +167,8 @@ void vtime_stop_cpu(void) 
	/* Wait for external, I/O or machine check interrupt. */

	psw.mask = psw_kernel_bits | PSW_MASK_WAIT | PSW_MASK_IO | PSW_MASK_EXT;



	idle->nohz_delay = 0;



	/* Check if the CPU timer needs to be reprogrammed. */

	if (vq->do_spt) {

		__u64 vmax = VTIMER_MAX_SLICE;

drivers/s390/cio/cio.c

+1 −0
Original line number Diff line number Diff line
@@ -618,6 +618,7 @@ void __irq_entry do_IRQ(struct pt_regs *regs) 
	old_regs = set_irq_regs(regs);

	s390_idle_check();

	irq_enter();

	__get_cpu_var(s390_idle).nohz_delay = 1;

	if (S390_lowcore.int_clock >= S390_lowcore.clock_comparator)

		/* Serve timer interrupts first. */

		clock_comparator_work();

include/linux/tick.h

+3 −0
Original line number Diff line number Diff line
@@ -98,6 +98,9 @@ extern int tick_check_oneshot_change(int allow_nohz); 
extern struct tick_sched *tick_get_tick_sched(int cpu);

extern void tick_check_idle(int cpu);

extern int tick_oneshot_mode_active(void);

#  ifndef arch_needs_cpu

#   define arch_needs_cpu(cpu) (0)

#  endif

# else

static inline void tick_clock_notify(void) { }

static inline int tick_check_oneshot_change(int allow_nohz) { return 0; }