From: Martin Schwidefsky <schwidefsky@xxxxxxxxxx>
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@xxxxxxxxxx>
---
arch/s390/include/asm/cputime.h | 8 ++++++++
arch/s390/kernel/s390_ext.c | 2 ++
arch/s390/kernel/vtime.c | 2 ++
drivers/s390/cio/cio.c | 1 +
include/linux/tick.h | 3 +++
kernel/time/tick-sched.c | 13 ++++++++-----
6 files changed, 24 insertions(+), 5 deletions(-)
Index: quilt-2.6/arch/s390/include/asm/cputime.h
===================================================================
--- quilt-2.6.orig/arch/s390/include/asm/cputime.h 2009-08-14 13:17:23.000000000 +0200
+++ quilt-2.6/arch/s390/include/asm/cputime.h 2009-09-18 14:08:13.000000000 +0200
@@ -182,6 +182,7 @@
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);
@@ -197,4 +198,11 @@
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 */
Index: quilt-2.6/arch/s390/kernel/s390_ext.c
===================================================================
--- quilt-2.6.orig/arch/s390/kernel/s390_ext.c 2009-08-14 13:17:23.000000000 +0200
+++ quilt-2.6/arch/s390/kernel/s390_ext.c 2009-09-18 14:08:13.000000000 +0200
@@ -126,6 +126,8 @@
/* 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))
Index: quilt-2.6/arch/s390/kernel/vtime.c
===================================================================
--- quilt-2.6.orig/arch/s390/kernel/vtime.c 2009-08-14 13:17:23.000000000 +0200
+++ quilt-2.6/arch/s390/kernel/vtime.c 2009-09-18 14:08:13.000000000 +0200
@@ -167,6 +167,8 @@
/* 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;
Index: quilt-2.6/drivers/s390/cio/cio.c
===================================================================
--- quilt-2.6.orig/drivers/s390/cio/cio.c 2009-09-12 09:47:15.000000000 +0200
+++ quilt-2.6/drivers/s390/cio/cio.c 2009-09-18 14:08:13.000000000 +0200
@@ -618,6 +618,7 @@
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();
Index: quilt-2.6/include/linux/tick.h
===================================================================
--- quilt-2.6.orig/include/linux/tick.h 2009-08-07 11:09:40.000000000 +0200
+++ quilt-2.6/include/linux/tick.h 2009-09-18 14:08:13.000000000 +0200
@@ -98,6 +98,9 @@
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; }
Index: quilt-2.6/kernel/time/tick-sched.c
===================================================================
--- quilt-2.6.orig/kernel/time/tick-sched.c 2009-08-07 11:09:40.000000000 +0200
+++ quilt-2.6/kernel/time/tick-sched.c 2009-09-18 14:08:14.000000000 +0200
@@ -272,12 +272,15 @@
last_jiffies = jiffies;
} while (read_seqretry(&xtime_lock, seq));
- /* Get the next timer wheel timer */
- next_jiffies = get_next_timer_interrupt(last_jiffies);
- delta_jiffies = next_jiffies - last_jiffies;
-
- if (rcu_needs_cpu(cpu) || printk_needs_cpu(cpu))
+ if (rcu_needs_cpu(cpu) || printk_needs_cpu(cpu) ||
+ arch_needs_cpu(cpu)) {
+ next_jiffies = last_jiffies + 1;
delta_jiffies = 1;
+ } else {
+ /* Get the next timer wheel timer */
+ next_jiffies = get_next_timer_interrupt(last_jiffies);
+ delta_jiffies = next_jiffies - last_jiffies;
+ }
/*
* Do not stop the tick, if we are only one off
* or if the cpu is required for rcu
--
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