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Message-Id: <1250001100-3936-2-git-send-email-sgruszka@redhat.com>
Date: Tue, 11 Aug 2009 16:31:40 +0200
From: Stanislaw Gruszka <sgruszka@...hat.com>
To: Ingo Molnar <mingo@...e.hu>
Cc: Thomas Gleixner <tglx@...utronix.de>, linux-kernel@...r.kernel.org,
Oleg Nesterov <oleg@...hat.com>,
Peter Zijlstra <a.p.zijlstra@...llo.nl>,
Stanislaw Gruszka <sgruszka@...hat.com>
Subject: [PATCH -tip 1/1] posix-cpu-timers: fix CPUCLOCK_{PROF,VIRT} periodic tics precision
When calculating next expires time and timer overrun value for periodic
timer use real nanosecond interval value provided by user (same 64 bits
algorithm as for CPUCLOCK_SCHED). Then round up values for cputime
resolution based on nanosecond value of one cpu tick.
Signed-off-by: Stanislaw Gruszka <sgruszka@...hat.com>
---
include/linux/posix-timers.h | 17 ++++++++
kernel/itimer.c | 11 -----
kernel/posix-cpu-timers.c | 92 +++++++++++++++++++++++++++--------------
3 files changed, 77 insertions(+), 43 deletions(-)
diff --git a/include/linux/posix-timers.h b/include/linux/posix-timers.h
index 4f71bf4..68a129e 100644
--- a/include/linux/posix-timers.h
+++ b/include/linux/posix-timers.h
@@ -13,7 +13,9 @@ union cpu_time_count {
struct cpu_timer_list {
struct list_head entry;
union cpu_time_count expires, incr;
+ u64 real_incr;
struct task_struct *task;
+ u32 error;
int firing;
};
@@ -119,4 +121,19 @@ long clock_nanosleep_restart(struct restart_block *restart_block);
void update_rlimit_cpu(unsigned long rlim_new);
+/*
+ * Helper for calculating error when rounding time values providing
+ * in nano or micro seconds to cputime_t ticks.
+ */
+static inline u32 cputime_sub_ns(cputime_t ct, s64 real_ns)
+{
+ struct timespec ts;
+ s64 cpu_ns;
+
+ cputime_to_timespec(ct, &ts);
+ cpu_ns = timespec_to_ns(&ts);
+
+ return (cpu_ns <= real_ns) ? 0 : cpu_ns - real_ns;
+}
+
#endif
diff --git a/kernel/itimer.c b/kernel/itimer.c
index 8078a32..607cb7d 100644
--- a/kernel/itimer.c
+++ b/kernel/itimer.c
@@ -127,17 +127,6 @@ enum hrtimer_restart it_real_fn(struct hrtimer *timer)
return HRTIMER_NORESTART;
}
-static inline u32 cputime_sub_ns(cputime_t ct, s64 real_ns)
-{
- struct timespec ts;
- s64 cpu_ns;
-
- cputime_to_timespec(ct, &ts);
- cpu_ns = timespec_to_ns(&ts);
-
- return (cpu_ns <= real_ns) ? 0 : cpu_ns - real_ns;
-}
-
static void set_cpu_itimer(struct task_struct *tsk, unsigned int clock_id,
const struct itimerval *const value,
struct itimerval *const ovalue)
diff --git a/kernel/posix-cpu-timers.c b/kernel/posix-cpu-timers.c
index 12161f7..2a32c9a 100644
--- a/kernel/posix-cpu-timers.c
+++ b/kernel/posix-cpu-timers.c
@@ -117,6 +117,11 @@ static inline cputime_t cputime_div_non_zero(cputime_t time, unsigned long div)
}
/*
+ * One jiffy in nanoseconds, calculated using real frequency of hardware timer.
+ */
+static u32 onecputick;
+
+/*
* Update expiry time from increment, and increase overrun count,
* given the current clock sample.
*/
@@ -124,46 +129,60 @@ static void bump_cpu_timer(struct k_itimer *timer,
union cpu_time_count now)
{
int i;
+ unsigned long long now_ns, expires, delta, incr;
if (timer->it.cpu.incr.sched == 0)
return;
if (CPUCLOCK_WHICH(timer->it_clock) == CPUCLOCK_SCHED) {
- unsigned long long delta, incr;
-
if (now.sched < timer->it.cpu.expires.sched)
return;
+
+ now_ns = now.sched;
+ expires = timer->it.cpu.expires.sched;
incr = timer->it.cpu.incr.sched;
- delta = now.sched + incr - timer->it.cpu.expires.sched;
- /* Don't use (incr*2 < delta), incr*2 might overflow. */
- for (i = 0; incr < delta - incr; i++)
- incr = incr << 1;
- for (; i >= 0; incr >>= 1, i--) {
- if (delta < incr)
- continue;
- timer->it.cpu.expires.sched += incr;
- timer->it_overrun += 1 << i;
- delta -= incr;
- }
} else {
- cputime_t delta, incr;
-
if (cputime_lt(now.cpu, timer->it.cpu.expires.cpu))
return;
- incr = timer->it.cpu.incr.cpu;
- delta = cputime_sub(cputime_add(now.cpu, incr),
- timer->it.cpu.expires.cpu);
- /* Don't use (incr*2 < delta), incr*2 might overflow. */
- for (i = 0; cputime_lt(incr, cputime_sub(delta, incr)); i++)
- incr = cputime_add(incr, incr);
- for (; i >= 0; incr = cputime_halve(incr), i--) {
- if (cputime_lt(delta, incr))
- continue;
- timer->it.cpu.expires.cpu =
- cputime_add(timer->it.cpu.expires.cpu, incr);
- timer->it_overrun += 1 << i;
- delta = cputime_sub(delta, incr);
+
+ now_ns = cputime_to_jiffies(now.cpu);
+ now_ns *= onecputick;
+
+ expires = cputime_to_jiffies(timer->it.cpu.expires.cpu);
+ expires *= onecputick;
+ expires -= timer->it.cpu.error;
+
+ incr = timer->it.cpu.real_incr;
+ }
+
+ delta = now_ns + incr - expires;
+
+ /* Don't use (incr*2 < delta), incr*2 might overflow. */
+ for (i = 0; incr < delta - incr; i++)
+ incr = incr << 1;
+ for (; i >= 0; incr >>= 1, i--) {
+ if (delta < incr)
+ continue;
+ expires += incr;
+ timer->it_overrun += 1 << i;
+ delta -= incr;
+ }
+
+ if (CPUCLOCK_WHICH(timer->it_clock) == CPUCLOCK_SCHED)
+ timer->it.cpu.expires.sched = expires;
+ else {
+ unsigned long exp_jiffy;
+ u32 error;
+
+ error = do_div(expires, onecputick);
+ if (error == 0) {
+ exp_jiffy = expires;
+ timer->it.cpu.error = 0;
+ } else {
+ exp_jiffy = expires + 1;
+ timer->it.cpu.error = onecputick - error;
}
+ timer->it.cpu.expires.cpu = jiffies_to_cputime(exp_jiffy);
}
}
@@ -397,6 +416,8 @@ int posix_cpu_timer_create(struct k_itimer *new_timer)
INIT_LIST_HEAD(&new_timer->it.cpu.entry);
new_timer->it.cpu.incr.sched = 0;
new_timer->it.cpu.expires.sched = 0;
+ new_timer->it.cpu.error = 0;
+ new_timer->it.cpu.real_incr = 0;
read_lock(&tasklist_lock);
if (CPUCLOCK_PERTHREAD(new_timer->it_clock)) {
@@ -842,6 +863,14 @@ int posix_cpu_timer_set(struct k_itimer *timer, int flags,
timer->it.cpu.incr = timespec_to_sample(timer->it_clock,
&new->it_interval);
+ if (CPUCLOCK_WHICH(timer->it_clock) != CPUCLOCK_SCHED) {
+ cputime_t val = timespec_to_cputime(&new->it_value);
+ s64 ns_val = timespec_to_ns(&new->it_value);
+
+ timer->it.cpu.real_incr = timespec_to_ns(&new->it_interval);
+ timer->it.cpu.error = cputime_sub_ns(val, ns_val);
+ }
+
/*
* This acts as a modification timestamp for the timer,
* so any automatic reload attempt will punt on seeing
@@ -1073,7 +1102,6 @@ static void stop_process_timers(struct task_struct *tsk)
spin_unlock_irqrestore(&cputimer->lock, flags);
}
-static u32 onecputick;
static void check_cpu_itimer(struct task_struct *tsk, struct cpu_itimer *it,
cputime_t *expires, cputime_t cur_time, int signo)
@@ -1710,13 +1738,13 @@ static __init int init_posix_cpu_timers(void)
};
struct timespec ts;
- register_posix_clock(CLOCK_PROCESS_CPUTIME_ID, &process);
- register_posix_clock(CLOCK_THREAD_CPUTIME_ID, &thread);
-
cputime_to_timespec(cputime_one_jiffy, &ts);
onecputick = ts.tv_nsec;
WARN_ON(ts.tv_sec != 0);
+ register_posix_clock(CLOCK_PROCESS_CPUTIME_ID, &process);
+ register_posix_clock(CLOCK_THREAD_CPUTIME_ID, &thread);
+
return 0;
}
__initcall(init_posix_cpu_timers);
--
1.6.2.5
--
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