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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: Martin Schwidefsky <schwidefsky@de.ibm.com> LKML-Reference: <20090929122533.402715150@de.ibm.com> Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
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6 changed files with 24 additions and 5 deletions
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@ -183,6 +183,7 @@ struct s390_idle_data {
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unsigned long long idle_count;
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unsigned long long idle_enter;
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unsigned long long idle_time;
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int nohz_delay;
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};
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DECLARE_PER_CPU(struct s390_idle_data, s390_idle);
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@ -198,4 +199,11 @@ static inline void s390_idle_check(void)
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vtime_start_cpu();
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}
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static inline int s390_nohz_delay(int cpu)
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{
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return per_cpu(s390_idle, cpu).nohz_delay != 0;
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}
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#define arch_needs_cpu(cpu) s390_nohz_delay(cpu)
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#endif /* _S390_CPUTIME_H */
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@ -126,6 +126,8 @@ void __irq_entry do_extint(struct pt_regs *regs, unsigned short code)
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/* Serve timer interrupts first. */
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clock_comparator_work();
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kstat_cpu(smp_processor_id()).irqs[EXTERNAL_INTERRUPT]++;
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if (code != 0x1004)
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__get_cpu_var(s390_idle).nohz_delay = 1;
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index = ext_hash(code);
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for (p = ext_int_hash[index]; p; p = p->next) {
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if (likely(p->code == code))
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@ -167,6 +167,8 @@ void vtime_stop_cpu(void)
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/* Wait for external, I/O or machine check interrupt. */
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psw.mask = psw_kernel_bits | PSW_MASK_WAIT | PSW_MASK_IO | PSW_MASK_EXT;
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idle->nohz_delay = 0;
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/* Check if the CPU timer needs to be reprogrammed. */
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if (vq->do_spt) {
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__u64 vmax = VTIMER_MAX_SLICE;
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@ -618,6 +618,7 @@ void __irq_entry do_IRQ(struct pt_regs *regs)
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old_regs = set_irq_regs(regs);
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s390_idle_check();
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irq_enter();
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__get_cpu_var(s390_idle).nohz_delay = 1;
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if (S390_lowcore.int_clock >= S390_lowcore.clock_comparator)
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/* Serve timer interrupts first. */
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clock_comparator_work();
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@ -98,6 +98,9 @@ extern int tick_check_oneshot_change(int allow_nohz);
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extern struct tick_sched *tick_get_tick_sched(int cpu);
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extern void tick_check_idle(int cpu);
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extern int tick_oneshot_mode_active(void);
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# ifndef arch_needs_cpu
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# define arch_needs_cpu(cpu) (0)
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# endif
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# else
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static inline void tick_clock_notify(void) { }
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static inline int tick_check_oneshot_change(int allow_nohz) { return 0; }
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@ -264,12 +264,15 @@ void tick_nohz_stop_sched_tick(int inidle)
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last_jiffies = jiffies;
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} while (read_seqretry(&xtime_lock, seq));
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/* Get the next timer wheel timer */
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next_jiffies = get_next_timer_interrupt(last_jiffies);
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delta_jiffies = next_jiffies - last_jiffies;
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if (rcu_needs_cpu(cpu) || printk_needs_cpu(cpu))
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if (rcu_needs_cpu(cpu) || printk_needs_cpu(cpu) ||
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arch_needs_cpu(cpu)) {
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next_jiffies = last_jiffies + 1;
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delta_jiffies = 1;
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} else {
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/* Get the next timer wheel timer */
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next_jiffies = get_next_timer_interrupt(last_jiffies);
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delta_jiffies = next_jiffies - last_jiffies;
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}
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/*
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* Do not stop the tick, if we are only one off
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* or if the cpu is required for rcu
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