[PATCH RFC v3 5/6] tick: get duration of the last idle loop

[PATCH RFC v3 5/6] tick: get duration of the last idle loop

[Quan Xu]

From: Quan Xu <quan.xu0@gmail.com>

the last idle loop is from tick_nohz_idle_enter to tick_nohz_idle_exit.

Signed-off-by: Yang Zhang <yang.zhang.wz@gmail.com>
Signed-off-by: Quan Xu <quan.xu0@gmail.com>
Cc: Frederic Weisbecker <fweisbec@gmail.com>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Ingo Molnar <mingo@kernel.org>
Cc: linux-kernel@vger.kernel.org
---
 include/linux/tick.h     |    2 ++
 kernel/time/tick-sched.c |   11 +++++++++++
 kernel/time/tick-sched.h |    3 +++
 3 files changed, 16 insertions(+), 0 deletions(-)

diff --git a/include/linux/tick.h b/include/linux/tick.h
index cf413b3..77ae46d 100644
--- a/include/linux/tick.h
+++ b/include/linux/tick.h
@@ -118,6 +118,7 @@ enum tick_dep_bits {
 extern void tick_nohz_idle_exit(void);
 extern void tick_nohz_irq_exit(void);
 extern ktime_t tick_nohz_get_sleep_length(void);
+extern ktime_t tick_nohz_get_last_idle_length(void);
 extern unsigned long tick_nohz_get_idle_calls(void);
 extern u64 get_cpu_idle_time_us(int cpu, u64 *last_update_time);
 extern u64 get_cpu_iowait_time_us(int cpu, u64 *last_update_time);
@@ -127,6 +128,7 @@ enum tick_dep_bits {
 static inline void tick_nohz_idle_enter(void) { }
 static inline void tick_nohz_idle_exit(void) { }
 
+static ktime_t tick_nohz_get_last_idle_length(void) { return -1; }
 static inline ktime_t tick_nohz_get_sleep_length(void)
 {
 	return NSEC_PER_SEC / HZ;
diff --git a/kernel/time/tick-sched.c b/kernel/time/tick-sched.c
index c7a899c..65c9cc0 100644
--- a/kernel/time/tick-sched.c
+++ b/kernel/time/tick-sched.c
@@ -548,6 +548,7 @@ static void tick_nohz_update_jiffies(ktime_t now)
 		else
 			ts->idle_sleeptime = ktime_add(ts->idle_sleeptime, delta);
 		ts->idle_entrytime = now;
+		ts->idle_length = delta;
 	}
 
 	if (last_update_time)
@@ -998,6 +999,16 @@ void tick_nohz_irq_exit(void)
 }
 
 /**
+ * tick_nohz_get_last_idle_length - return the length of the last idle loop
+ */
+ktime_t tick_nohz_get_last_idle_length(void)
+{
+	struct tick_sched *ts = this_cpu_ptr(&tick_cpu_sched);
+
+	return ts->idle_length;
+}
+
+/**
  * tick_nohz_get_sleep_length - return the length of the current sleep
  *
  * Called from power state control code with interrupts disabled
diff --git a/kernel/time/tick-sched.h b/kernel/time/tick-sched.h
index 954b43d..2630cf9 100644
--- a/kernel/time/tick-sched.h
+++ b/kernel/time/tick-sched.h
@@ -39,6 +39,8 @@ enum tick_nohz_mode {
  * @idle_sleeptime:	Sum of the time slept in idle with sched tick stopped
  * @iowait_sleeptime:	Sum of the time slept in idle with sched tick stopped, with IO outstanding
  * @sleep_length:	Duration of the current idle sleep
+ * @idle_length:	Duration of the last idle loop is from
+ *			tick_nohz_idle_enter to tick_nohz_idle_exit.
  * @do_timer_lst:	CPU was the last one doing do_timer before going idle
  */
 struct tick_sched {
@@ -59,6 +61,7 @@ struct tick_sched {
 	ktime_t				idle_sleeptime;
 	ktime_t				iowait_sleeptime;
 	ktime_t				sleep_length;
+	ktime_t				idle_length;
 	unsigned long			last_jiffies;
 	u64				next_timer;
 	ktime_t				idle_expires;
-- 
1.7.1


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[PATCH RFC v3 6/6] KVM guest: introduce smart idle poll algorithm

[Quan Xu]

From: Yang Zhang <yang.zhang.wz@gmail.com>

using smart idle poll to reduce the useless poll when system is idle.

Signed-off-by: Quan Xu <quan.xu0@gmail.com>
Signed-off-by: Yang Zhang <yang.zhang.wz@gmail.com>
Cc: Paolo Bonzini <pbonzini@redhat.com>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Ingo Molnar <mingo@redhat.com>
Cc: "H. Peter Anvin" <hpa@zytor.com>
Cc: x86@kernel.org
Cc: kvm@vger.kernel.org
Cc: linux-kernel@vger.kernel.org
---
 arch/x86/kernel/kvm.c |   47 +++++++++++++++++++++++++++++++++++++++++++++++
 1 files changed, 47 insertions(+), 0 deletions(-)

diff --git a/arch/x86/kernel/kvm.c b/arch/x86/kernel/kvm.c
index 2a6e402..8bb6d55 100644
--- a/arch/x86/kernel/kvm.c
+++ b/arch/x86/kernel/kvm.c
@@ -37,6 +37,7 @@
 #include <linux/debugfs.h>
 #include <linux/nmi.h>
 #include <linux/swait.h>
+#include <linux/tick.h>
 #include <asm/timer.h>
 #include <asm/cpu.h>
 #include <asm/traps.h>
@@ -365,11 +366,57 @@ static void kvm_guest_cpu_init(void)
 		kvm_register_steal_time();
 }
 
+static unsigned int grow_poll_ns(unsigned int old, unsigned int grow,
+				 unsigned int max)
+{
+	unsigned int val;
+
+	/* set base poll time to 10000ns */
+	if (old == 0 && grow)
+		return 10000;
+
+	val = old * grow;
+	if (val > max)
+		val = max;
+
+	return val;
+}
+
+static unsigned int shrink_poll_ns(unsigned int old, unsigned int shrink)
+{
+	if (shrink == 0)
+		return 0;
+
+	return old / shrink;
+}
+
+static void kvm_idle_update_poll_duration(ktime_t idle)
+{
+	unsigned long poll_duration = this_cpu_read(poll_duration_ns);
+
+	/* so far poll duration is based on nohz */
+	if (idle == -1ULL)
+		return;
+
+	if (poll_duration && idle > paravirt_poll_threshold_ns)
+		poll_duration = shrink_poll_ns(poll_duration,
+					       paravirt_poll_shrink);
+	else if (poll_duration < paravirt_poll_threshold_ns &&
+		 idle < paravirt_poll_threshold_ns)
+		poll_duration = grow_poll_ns(poll_duration, paravirt_poll_grow,
+					     paravirt_poll_threshold_ns);
+
+	this_cpu_write(poll_duration_ns, poll_duration);
+}
+
 static void kvm_idle_poll(void)
 {
 	unsigned long poll_duration = this_cpu_read(poll_duration_ns);
+	ktime_t idle = tick_nohz_get_last_idle_length();
 	ktime_t start, cur, stop;
 
+	kvm_idle_update_poll_duration(idle);
+
 	start = cur = ktime_get();
 	stop = ktime_add_ns(ktime_get(), poll_duration);
 
-- 
1.7.1


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