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Date: Mon, 20 Apr 2009 16:16:05 -0500
From: Jon Hunter <jon-hunter@...com>
To: "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: [RFC][PATCH] Dynamic Tick: Allow 32-bit machines to sleep for more
than 2.15 seconds
Hello,
From reviewing the dynamic tick code, I noticed that the "max_delta_ns"
member of the "clock_event_device" structure, represents the upper limit
between timer events in nanoseconds. The variable, "max_delta_ns", is
defined as an unsigned long. An unsigned long is a 32-bit integer for
32-bit machines and is a 64-bit integer for 64-bit machines (if -m64
option is used for gcc). Also see [1].
The variable, "max_delta_ns", is configured by calling function
"clockevent_delta2ns()". The maximum value that "max_delta_ns" can be
set to by calling clockevent_delta2ns(), is LONG_MAX. For a 32-bit
machine LONG_MAX is equal to 0x7fffffff and in nanoseconds this equates
to ~2.15 seconds. Hence, the maximum sleep time for a 32-bit machine is
~2.15 seconds, where as for a 64-bit machine it will be many years.
Therefore, I wanted to propose changing the type of max_delta_ns to be
"unsigned long long" instead of "unsigned long". My understanding is
that a variable of type "unsigned long long" is 64-bits for both 32-bit
and 64-bit machines and hence this would allow a 32-bit machine to sleep
for longer than ~2.15 seconds. Please note that I also ended up making
"min_delta_ns" of type "unsigned long long" too and although this is
probably very unnecessary, it made the patch simpler. See below.
Anyway, making this change has allowed my 32-bit machine to sleep for
longer than ~2.15 seconds and thought this could be of interest to
others. Your comments/feedback would be appreciated.
[1] http://en.wikipedia.org/wiki/64-bit#64-bit_data_models
Cheers
Jon
Signed-off-by: Jon Hunter <jon-hunter@...com>
---
include/linux/clockchips.h | 6 +++---
kernel/hrtimer.c | 2 +-
kernel/time/clockevents.c | 10 +++++-----
kernel/time/tick-oneshot.c | 2 +-
kernel/time/timer_list.c | 4 ++--
5 files changed, 12 insertions(+), 12 deletions(-)
diff --git a/include/linux/clockchips.h b/include/linux/clockchips.h
index 3a1dbba..8154bc6 100644
--- a/include/linux/clockchips.h
+++ b/include/linux/clockchips.h
@@ -77,8 +77,8 @@ enum clock_event_nofitiers {
struct clock_event_device {
const char *name;
unsigned int features;
- unsigned long max_delta_ns;
- unsigned long min_delta_ns;
+ unsigned long long max_delta_ns;
+ unsigned long long min_delta_ns;
unsigned long mult;
int shift;
int rating;
@@ -116,7 +116,7 @@ static inline unsigned long div_sc(unsigned long
ticks, unsigned long nsec,
}
/* Clock event layer functions */
-extern unsigned long clockevent_delta2ns(unsigned long latch,
+extern unsigned long long clockevent_delta2ns(unsigned long latch,
struct clock_event_device *evt);
extern void clockevents_register_device(struct clock_event_device *dev);
diff --git a/kernel/hrtimer.c b/kernel/hrtimer.c
index cb8a15c..5b1cdc4 100644
--- a/kernel/hrtimer.c
+++ b/kernel/hrtimer.c
@@ -1199,7 +1199,7 @@ hrtimer_interrupt_hanging(struct
clock_event_device *dev,
force_clock_reprogram = 1;
dev->min_delta_ns = (unsigned long)try_time.tv64 * 3;
printk(KERN_WARNING "hrtimer: interrupt too slow, "
- "forcing clock min delta to %lu ns\n", dev->min_delta_ns);
+ "forcing clock min delta to %llu ns\n", dev->min_delta_ns);
}
/*
* High resolution timer interrupt
diff --git a/kernel/time/clockevents.c b/kernel/time/clockevents.c
index d13be21..3fa07b3 100644
--- a/kernel/time/clockevents.c
+++ b/kernel/time/clockevents.c
@@ -36,10 +36,10 @@ static DEFINE_SPINLOCK(clockevents_lock);
*
* Math helper, returns latch value converted to nanoseconds (bound
checked)
*/
-unsigned long clockevent_delta2ns(unsigned long latch,
+unsigned long long clockevent_delta2ns(unsigned long latch,
struct clock_event_device *evt)
{
- u64 clc = ((u64) latch << evt->shift);
+ unsigned long long clc = ((unsigned long long) latch << evt->shift);
if (unlikely(!evt->mult)) {
evt->mult = 1;
@@ -49,10 +49,10 @@ unsigned long clockevent_delta2ns(unsigned long latch,
do_div(clc, evt->mult);
if (clc < 1000)
clc = 1000;
- if (clc > LONG_MAX)
- clc = LONG_MAX;
+ if (clc > LLONG_MAX)
+ clc = LLONG_MAX;
- return (unsigned long) clc;
+ return clc;
}
/**
diff --git a/kernel/time/tick-oneshot.c b/kernel/time/tick-oneshot.c
index 2e8de67..857087b 100644
--- a/kernel/time/tick-oneshot.c
+++ b/kernel/time/tick-oneshot.c
@@ -50,7 +50,7 @@ int tick_dev_program_event(struct clock_event_device
*dev, ktime_t expires,
dev->min_delta_ns += dev->min_delta_ns >> 1;
printk(KERN_WARNING
- "CE: %s increasing min_delta_ns to %lu nsec\n",
+ "CE: %s increasing min_delta_ns to %llu nsec\n",
dev->name ? dev->name : "?",
dev->min_delta_ns << 1);
diff --git a/kernel/time/timer_list.c b/kernel/time/timer_list.c
index a999b92..3bf30b4 100644
--- a/kernel/time/timer_list.c
+++ b/kernel/time/timer_list.c
@@ -204,8 +204,8 @@ print_tickdevice(struct seq_file *m, struct
tick_device *td, int cpu)
return;
}
SEQ_printf(m, "%s\n", dev->name);
- SEQ_printf(m, " max_delta_ns: %lu\n", dev->max_delta_ns);
- SEQ_printf(m, " min_delta_ns: %lu\n", dev->min_delta_ns);
+ SEQ_printf(m, " max_delta_ns: %llu\n", dev->max_delta_ns);
+ SEQ_printf(m, " min_delta_ns: %llu\n", dev->min_delta_ns);
SEQ_printf(m, " mult: %lu\n", dev->mult);
SEQ_printf(m, " shift: %d\n", dev->shift);
SEQ_printf(m, " mode: %d\n", dev->mode);
--
1.6.1
--
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