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Date: Thu, 5 Nov 2009 06:57:55 GMT
From: tip-bot for Martin Schwidefsky <schwidefsky@...ibm.com>
To: linux-tip-commits@...r.kernel.org
Cc: linux-kernel@...r.kernel.org, hpa@...or.com, mingo@...hat.com,
schwidefsky@...ibm.com, tglx@...utronix.de
Subject: [tip:timers/core] nohz: Introduce arch_needs_cpu
Commit-ID: 3c5d92a0cfb5103c0d5ab74d4ae6373d3af38148
Gitweb: http://git.kernel.org/tip/3c5d92a0cfb5103c0d5ab74d4ae6373d3af38148
Author: Martin Schwidefsky <schwidefsky@...ibm.com>
AuthorDate: Tue, 29 Sep 2009 14:25:16 +0200
Committer: Thomas Gleixner <tglx@...utronix.de>
CommitDate: Thu, 5 Nov 2009 07:53:53 +0100
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@...ibm.com>
LKML-Reference: <20090929122533.402715150@...ibm.com>
Signed-off-by: Thomas Gleixner <tglx@...utronix.de>
---
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(-)
diff --git a/arch/s390/include/asm/cputime.h b/arch/s390/include/asm/cputime.h
index 24b1244..95f3561 100644
--- a/arch/s390/include/asm/cputime.h
+++ b/arch/s390/include/asm/cputime.h
@@ -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 */
diff --git a/arch/s390/kernel/s390_ext.c b/arch/s390/kernel/s390_ext.c
index 0de305b..59618bc 100644
--- a/arch/s390/kernel/s390_ext.c
+++ b/arch/s390/kernel/s390_ext.c
@@ -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))
diff --git a/arch/s390/kernel/vtime.c b/arch/s390/kernel/vtime.c
index c41bb0d..b59a812 100644
--- a/arch/s390/kernel/vtime.c
+++ b/arch/s390/kernel/vtime.c
@@ -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;
diff --git a/drivers/s390/cio/cio.c b/drivers/s390/cio/cio.c
index 138124f..126f240 100644
--- a/drivers/s390/cio/cio.c
+++ b/drivers/s390/cio/cio.c
@@ -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();
diff --git a/include/linux/tick.h b/include/linux/tick.h
index 0482229..8dc0821 100644
--- a/include/linux/tick.h
+++ b/include/linux/tick.h
@@ -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; }
diff --git a/kernel/time/tick-sched.c b/kernel/time/tick-sched.c
index 7378e2c..3840f6d 100644
--- a/kernel/time/tick-sched.c
+++ b/kernel/time/tick-sched.c
@@ -264,12 +264,15 @@ void tick_nohz_stop_sched_tick(int inidle)
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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