[patch 0/2] nohz tweaking

From: Martin Schwidefsky <schwidefsky.RemoveThis@de.ibm.com>

On a system with NOHZ=y tick_check_idle calls tick_nohz_stop_idle and
tick_nohz_update_jiffies. Given the right conditions (ts->idle_active
and/or ts->tick_stopped) both function get a time stamp with ktime_get.
The same time stamp can be reused if both function require one.

On s390 this change has the additional benefit that gcc inlines the
tick_nohz_stop_idle function into tick_check_idle. The number of
instructions to execute tick_check_idle drops from 225 to 144
(without the ktime_get optimization it is 367 vs 215 instructions).

before:

0) | tick_check_idle() {
0) | tick_nohz_stop_idle() {
0) | ktime_get() {
0) | read_tod_clock() {
0) 0.601 us | }
0) 1.765 us | }
0) 3.047 us | }
0) | ktime_get() {
0) | read_tod_clock() {
0) 0.570 us | }
0) 1.727 us | }
0) | tick_do_update_jiffies64() {
0) 0.609 us | }
0) 8.055 us | }

after:

0) | tick_check_idle() {
0) | ktime_get() {
0) | read_tod_clock() {
0) 0.617 us | }
0) 1.773 us | }
0) | tick_do_update_jiffies64() {
0) 0.593 us | }
0) 4.477 us | }

Cc: Ingo Molnar <mingo.RemoveThis@elte.hu>
Cc: Thomas Gleixner <tglx.RemoveThis@linutronix.de>
Cc: john stultz <johnstul.RemoveThis@us.ibm.com>
Signed-off-by: Martin Schwidefsky <schwidefsky.RemoveThis@de.ibm.com>
---

kernel/time/tick-sched.c | 62 +++++++++++++++++++++++++----------------------
1 file changed, 33 insertions(+), 29 deletions(-)

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 2009-09-29 14:15:43.000000000 +0200
@@ -134,18 +134,13 @@
* value. We do this unconditionally on any cpu, as we don't know whether the
* cpu, which has the update task assigned is in a long sleep.
*/
-static void tick_nohz_update_jiffies(void)
+static void tick_nohz_update_jiffies(ktime_t now)
{
int cpu = smp_processor_id();
struct tick_sched *ts = &per_cpu(tick_cpu_sched, cpu);
unsigned long flags;
- ktime_t now;
-
- if (!ts->tick_stopped)
- return;

cpumask_clear_cpu(cpu, nohz_cpu_mask);
- now = ktime_get();
ts->idle_waketime = now;

local_irq_save(flags);
@@ -155,20 +150,17 @@
touch_softlockup_watchdog();
}

-static void tick_nohz_stop_idle(int cpu)
+static void tick_nohz_stop_idle(int cpu, ktime_t now)
{
struct tick_sched *ts = &per_cpu(tick_cpu_sched, cpu);
+ ktime_t delta;

- if (ts->idle_active) {
- ktime_t now, delta;
- now = ktime_get();
- delta = ktime_sub(now, ts->idle_entrytime);
- ts->idle_lastupdate = now;
- ts->idle_sleeptime = ktime_add(ts->idle_sleeptime, delta);
- ts->idle_active = 0;
+ delta = ktime_sub(now, ts->idle_entrytime);
+ ts->idle_lastupdate = now;
+ ts->idle_sleeptime = ktime_add(ts->idle_sleeptime, delta);
+ ts->idle_active = 0;

- sched_clock_idle_wakeup_event(0);
- }
+ sched_clock_idle_wakeup_event(0);
}

static ktime_t tick_nohz_start_idle(struct tick_sched *ts)
@@ -431,7 +423,11 @@
ktime_t now;

local_irq_disable();
- tick_nohz_stop_idle(cpu);
+ if (ts->idle_active || (ts->inidle && ts->tick_stopped))
+ now = ktime_get();
+
+ if (ts->idle_active)
+ tick_nohz_stop_idle(cpu, now);

if (!ts->inidle || !ts->tick_stopped) {
ts->inidle = 0;
@@ -445,7 +441,6 @@

/* Update jiffies first */
select_nohz_load_balancer(0);
- now = ktime_get();
tick_do_update_jiffies64(now);
cpumask_clear_cpu(cpu, nohz_cpu_mask);

@@ -579,22 +574,18 @@
* timer and do not touch the other magic bits which need to be done
* when idle is left.
*/
-static void tick_nohz_kick_tick(int cpu)
+static void tick_nohz_kick_tick(int cpu, ktime_t now)
{
#if 0
/* Switch back to 2.6.27 behaviour */

struct tick_sched *ts = &per_cpu(tick_cpu_sched, cpu);
- ktime_t delta, now;
-
- if (!ts->tick_stopped)
- return;
+ ktime_t delta;

/*
* Do not touch the tick device, when the next expiry is either
* already reached or less/equal than the tick period.
*/
- now = ktime_get();
delta = ktime_sub(hrtimer_get_expires(&ts->sched_timer), now);
if (delta.tv64 <= tick_period.tv64)
return;
@@ -603,9 +594,26 @@
#endif
}

+static inline void tick_check_nohz(int cpu)
+{
+ struct tick_sched *ts = &per_cpu(tick_cpu_sched, cpu);
+ ktime_t now;
+
+ if (!ts->idle_active && !ts->tick_stopped)
+ return;
+ now = ktime_get();
+ if (ts->idle_active)
+ tick_nohz_stop_idle(cpu, now);
+ if (ts->tick_stopped) {
+ tick_nohz_update_jiffies(now);
+ tick_nohz_kick_tick(cpu, now);
+ }
+}
+
#else

static inline void tick_nohz_switch_to_nohz(void) { }
+static inline void tick_check_nohz(int cpu) { }

#endif /* NO_HZ */

@@ -615,11 +623,7 @@
void tick_check_idle(int cpu)
{
tick_check_oneshot_broadcast(cpu);
-#ifdef CONFIG_NO_HZ
- tick_nohz_stop_idle(cpu);
- tick_nohz_update_jiffies();
- tick_nohz_kick_tick(cpu);
-#endif
+ tick_check_nohz(cpu);
}

/*

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Martin,

On Tue, 29 Sep 2009, Martin Schwidefsky wrote:

> Greetings,
> the two remainting patches of the nohz performance work I've been
> doing. Both have been sent to the mailing lists before. Ingo had
> a comment about patch #1, but no one but me seems to be interested
> in patch #2. Neverless I would like to get both patches upstream.
> I can create a branch for them on git390 but I feel that they should
> go the path all the other nohz/time/clocksource patches went.

Sorry, that's my fault. I forgot them over the watchdog
wreckage. Picking them up now.

Thanks,

tglx
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On Wed, 30 Sep 2009 12:06:42 +0200 (CEST)
Thomas Gleixner <tglx.RemoveThis@linutronix.de> wrote:

> Martin,
>
> On Tue, 29 Sep 2009, Martin Schwidefsky wrote:
>
> > Greetings,
> > the two remainting patches of the nohz performance work I've been
> > doing. Both have been sent to the mailing lists before. Ingo had
> > a comment about patch #1, but no one but me seems to be interested
> > in patch #2. Neverless I would like to get both patches upstream.
> > I can create a branch for them on git390 but I feel that they should
> > go the path all the other nohz/time/clocksource patches went.
>
> Sorry, that's my fault. I forgot them over the watchdog
> wreckage. Picking them up now.

Thats great, thanks. And yes the clocksource/watchdog problems have
been painful..

--
blue skies,
Martin.

"Reality continues to ruin my life." - Calvin.

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Moin Thomas,

On Wed, 30 Sep 2009 12:06:42 +0200 (CEST)
Thomas Gleixner <tglx DeleteThis @linutronix.de> wrote:

> Martin,
>
> On Tue, 29 Sep 2009, Martin Schwidefsky wrote:
>
> > Greetings,
> > the two remainting patches of the nohz performance work I've been
> > doing. Both have been sent to the mailing lists before. Ingo had
> > a comment about patch #1, but no one but me seems to be interested
> > in patch #2. Neverless I would like to get both patches upstream.
> > I can create a branch for them on git390 but I feel that they should
> > go the path all the other nohz/time/clocksource patches went.
>
> Sorry, that's my fault. I forgot them over the watchdog
> wreckage. Picking them up now.

I could not find the patches on tip timers/core. Where did you put them ?

--
blue skies,
Martin.

"Reality continues to ruin my life." - Calvin.

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Commit-ID: eed3b9cf3fe3fcc7a50238dfcab63a63914e8f42
Gitweb: http://git.kernel.org/tip/eed3b9cf3fe3fcc7a50238dfcab63a63914e8f42
Author: Martin Schwidefsky <schwidefsky.TakeThisOut@de.ibm.com>
AuthorDate: Tue, 29 Sep 2009 14:25:15 +0200
Committer: Thomas Gleixner <tglx.TakeThisOut@linutronix.de>
CommitDate: Thu, 5 Nov 2009 07:53:53 +0100

nohz: Reuse ktime in sub-functions of tick_check_idle.

On a system with NOHZ=y tick_check_idle calls tick_nohz_stop_idle and
tick_nohz_update_jiffies. Given the right conditions (ts->idle_active
and/or ts->tick_stopped) both function get a time stamp with ktime_get.
The same time stamp can be reused if both function require one.

On s390 this change has the additional benefit that gcc inlines the
tick_nohz_stop_idle function into tick_check_idle. The number of
instructions to execute tick_check_idle drops from 225 to 144
(without the ktime_get optimization it is 367 vs 215 instructions).

before:

0) | tick_check_idle() {
0) | tick_nohz_stop_idle() {
0) | ktime_get() {
0) | read_tod_clock() {
0) 0.601 us | }
0) 1.765 us | }
0) 3.047 us | }
0) | ktime_get() {
0) | read_tod_clock() {
0) 0.570 us | }
0) 1.727 us | }
0) | tick_do_update_jiffies64() {
0) 0.609 us | }
0) 8.055 us | }

after:

0) | tick_check_idle() {
0) | ktime_get() {
0) | read_tod_clock() {
0) 0.617 us | }
0) 1.773 us | }
0) | tick_do_update_jiffies64() {
0) 0.593 us | }
0) 4.477 us | }

Signed-off-by: Martin Schwidefsky <schwidefsky.TakeThisOut@de.ibm.com>
Cc: john stultz <johnstul.TakeThisOut@us.ibm.com>
LKML-Reference: <20090929122533.206589318.TakeThisOut@de.ibm.com>
Signed-off-by: Thomas Gleixner <tglx.TakeThisOut@linutronix.de>
---
kernel/time/tick-sched.c | 62 ++++++++++++++++++++++++---------------------
1 files changed, 33 insertions(+), 29 deletions(-)

diff --git a/kernel/time/tick-sched.c b/kernel/time/tick-sched.c
index e0f59a2..7378e2c 100644
--- a/kernel/time/tick-sched.c
+++ b/kernel/time/tick-sched.c
@@ -134,18 +134,13 @@ __setup("nohz=", setup_tick_nohz);
* value. We do this unconditionally on any cpu, as we don't know whether the
* cpu, which has the update task assigned is in a long sleep.
*/
-static void tick_nohz_update_jiffies(void)
+static void tick_nohz_update_jiffies(ktime_t now)
{
int cpu = smp_processor_id();
struct tick_sched *ts = &per_cpu(tick_cpu_sched, cpu);
unsigned long flags;
- ktime_t now;
-
- if (!ts->tick_stopped)
- return;

cpumask_clear_cpu(cpu, nohz_cpu_mask);
- now = ktime_get();
ts->idle_waketime = now;

local_irq_save(flags);
@@ -155,20 +150,17 @@ static void tick_nohz_update_jiffies(void)
touch_softlockup_watchdog();
}

-static void tick_nohz_stop_idle(int cpu)
+static void tick_nohz_stop_idle(int cpu, ktime_t now)
{
struct tick_sched *ts = &per_cpu(tick_cpu_sched, cpu);
+ ktime_t delta;

- if (ts->idle_active) {
- ktime_t now, delta;
- now = ktime_get();
- delta = ktime_sub(now, ts->idle_entrytime);
- ts->idle_lastupdate = now;
- ts->idle_sleeptime = ktime_add(ts->idle_sleeptime, delta);
- ts->idle_active = 0;
+ delta = ktime_sub(now, ts->idle_entrytime);
+ ts->idle_lastupdate = now;
+ ts->idle_sleeptime = ktime_add(ts->idle_sleeptime, delta);
+ ts->idle_active = 0;

- sched_clock_idle_wakeup_event(0);
- }
+ sched_clock_idle_wakeup_event(0);
}

static ktime_t tick_nohz_start_idle(struct tick_sched *ts)
@@ -431,7 +423,11 @@ void tick_nohz_restart_sched_tick(void)
ktime_t now;

local_irq_disable();
- tick_nohz_stop_idle(cpu);
+ if (ts->idle_active || (ts->inidle && ts->tick_stopped))
+ now = ktime_get();
+
+ if (ts->idle_active)
+ tick_nohz_stop_idle(cpu, now);

if (!ts->inidle || !ts->tick_stopped) {
ts->inidle = 0;
@@ -445,7 +441,6 @@ void tick_nohz_restart_sched_tick(void)

/* Update jiffies first */
select_nohz_load_balancer(0);
- now = ktime_get();
tick_do_update_jiffies64(now);
cpumask_clear_cpu(cpu, nohz_cpu_mask);

@@ -579,22 +574,18 @@ static void tick_nohz_switch_to_nohz(void)
* timer and do not touch the other magic bits which need to be done
* when idle is left.
*/
-static void tick_nohz_kick_tick(int cpu)
+static void tick_nohz_kick_tick(int cpu, ktime_t now)
{
#if 0
/* Switch back to 2.6.27 behaviour */

struct tick_sched *ts = &per_cpu(tick_cpu_sched, cpu);
- ktime_t delta, now;
-
- if (!ts->tick_stopped)
- return;
+ ktime_t delta;

/*
* Do not touch the tick device, when the next expiry is either
* already reached or less/equal than the tick period.
*/
- now = ktime_get();
delta = ktime_sub(hrtimer_get_expires(&ts->sched_timer), now);
if (delta.tv64 <= tick_period.tv64)
return;
@@ -603,9 +594,26 @@ static void tick_nohz_kick_tick(int cpu)
#endif
}

+static inline void tick_check_nohz(int cpu)
+{
+ struct tick_sched *ts = &per_cpu(tick_cpu_sched, cpu);
+ ktime_t now;
+
+ if (!ts->idle_active && !ts->tick_stopped)
+ return;
+ now = ktime_get();
+ if (ts->idle_active)
+ tick_nohz_stop_idle(cpu, now);
+ if (ts->tick_stopped) {
+ tick_nohz_update_jiffies(now);
+ tick_nohz_kick_tick(cpu, now);
+ }
+}
+
#else

static inline void tick_nohz_switch_to_nohz(void) { }
+static inline void tick_check_nohz(int cpu) { }

#endif /* NO_HZ */

@@ -615,11 +623,7 @@ static inline void tick_nohz_switch_to_nohz(void) { }
void tick_check_idle(int cpu)
{
tick_check_oneshot_broadcast(cpu);
-#ifdef CONFIG_NO_HZ
- tick_nohz_stop_idle(cpu);
- tick_nohz_update_jiffies();
- tick_nohz_kick_tick(cpu);
-#endif
+ tick_check_nohz(cpu);
}

/*
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Commit-ID: 3c5d92a0cfb5103c0d5ab74d4ae6373d3af38148
Gitweb: http://git.kernel.org/tip/3c5d92a0cfb5103c0d5ab74d4ae6373d3af38148
Author: Martin Schwidefsky <schwidefsky DeleteThis @de.ibm.com>
AuthorDate: Tue, 29 Sep 2009 14:25:16 +0200
Committer: Thomas Gleixner <tglx DeleteThis @linutronix.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 DeleteThis @de.ibm.com>
LKML-Reference: <20090929122533.402715150 DeleteThis @de.ibm.com>
Signed-off-by: Thomas Gleixner <tglx DeleteThis @linutronix.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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* Martin Schwidefsky <schwidefsky.TakeThisOut@de.ibm.com> wrote:

> Moin Thomas,
>
> On Wed, 30 Sep 2009 12:06:42 +0200 (CEST)
> Thomas Gleixner <tglx.TakeThisOut@linutronix.de> wrote:
>
> > Martin,
> >
> > On Tue, 29 Sep 2009, Martin Schwidefsky wrote:
> >
> > > Greetings,
> > > the two remainting patches of the nohz performance work I've been
> > > doing. Both have been sent to the mailing lists before. Ingo had
> > > a comment about patch #1, but no one but me seems to be interested
> > > in patch #2. Neverless I would like to get both patches upstream.
> > > I can create a branch for them on git390 but I feel that they should
> > > go the path all the other nohz/time/clocksource patches went.
> >
> > Sorry, that's my fault. I forgot them over the watchdog
> > wreckage. Picking them up now.
>
> I could not find the patches on tip timers/core. Where did you put them ?

these are the currently pending patches in tip:timers/core:

3c5d92a: nohz: Introduce arch_needs_cpu
eed3b9c: nohz: Reuse ktime in sub-functions of tick_check_idle.
7bc7d63: time: Remove xtime_cache
a092ff0: time: Implement logarithmic time accumulation

Ingo
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Hi Ingo,

On Fri, 6 Nov 2009 09:41:38 +0100
Ingo Molnar <mingo.DeleteThis@elte.hu> wrote:

> * Martin Schwidefsky <schwidefsky.DeleteThis@de.ibm.com> wrote:
>
> > Moin Thomas,
> >
> > On Wed, 30 Sep 2009 12:06:42 +0200 (CEST)
> > Thomas Gleixner <tglx.DeleteThis@linutronix.de> wrote:
> >
> > > Martin,
> > >
> > > On Tue, 29 Sep 2009, Martin Schwidefsky wrote:
> > >
> > > > Greetings,
> > > > the two remainting patches of the nohz performance work I've been
> > > > doing. Both have been sent to the mailing lists before. Ingo had
> > > > a comment about patch #1, but no one but me seems to be interested
> > > > in patch #2. Neverless I would like to get both patches upstream.
> > > > I can create a branch for them on git390 but I feel that they should
> > > > go the path all the other nohz/time/clocksource patches went.
> > >
> > > Sorry, that's my fault. I forgot them over the watchdog
> > > wreckage. Picking them up now.
> >
> > I could not find the patches on tip timers/core. Where did you put them ?
>
> these are the currently pending patches in tip:timers/core:
>
> 3c5d92a: nohz: Introduce arch_needs_cpu
> eed3b9c: nohz: Reuse ktime in sub-functions of tick_check_idle.
> 7bc7d63: time: Remove xtime_cache
> a092ff0: time: Implement logarithmic time accumulation

Thanks for the list. Thomas added 3c5d92a and eed3b9c yesterday and
I am happy now. I have two more optimization patches for the clockevents
code, but I'm not don't quite content with them yet.

--
blue skies,
Martin.

"Reality continues to ruin my life." - Calvin.

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