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authorStanislaw Gruszka <sgruszka@redhat.com>2009-07-29 12:15:27 +0200
committerIngo Molnar <mingo@elte.hu>2009-08-03 14:48:35 +0200
commit8356b5f9c424e5831715abbce747197c30d1fd71 (patch)
tree87de74cc86f6eebf88eba9a4c335614787d984c5 /kernel
parent42c4ab41a176ee784c0f28c0b29025a8fc34f05a (diff)
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itimers: Fix periodic tics precision
Measure ITIMER_PROF and ITIMER_VIRT timers interval error between real ticks and requested by user. Take it into account when scheduling next tick. This patch introduce possibility where time between two consecutive tics is smaller then requested interval, it preserve however dependency that n tick is generated not earlier than n*interval time - counting from the beginning of periodic signal generation. Signed-off-by: Stanislaw Gruszka <sgruszka@redhat.com> Acked-by: Peter Zijlstra <a.p.zijlstra@chello.nl> Acked-by: Thomas Gleixner <tglx@linutronix.de> Cc: Oleg Nesterov <oleg@redhat.com> Cc: Andrew Morton <akpm@linux-foundation.org> Cc: Paul Mackerras <paulus@samba.org> Cc: Benjamin Herrenschmidt <benh@kernel.crashing.org> LKML-Reference: <1248862529-6063-3-git-send-email-sgruszka@redhat.com> Signed-off-by: Ingo Molnar <mingo@elte.hu>
Diffstat (limited to 'kernel')
-rw-r--r--kernel/itimer.c24
-rw-r--r--kernel/posix-cpu-timers.c20
2 files changed, 38 insertions, 6 deletions
diff --git a/kernel/itimer.c b/kernel/itimer.c
index 852c88d..21adff7 100644
--- a/kernel/itimer.c
+++ b/kernel/itimer.c
@@ -42,7 +42,7 @@ static struct timeval itimer_get_remtime(struct hrtimer *timer)
}
static void get_cpu_itimer(struct task_struct *tsk, unsigned int clock_id,
- struct itimerval *value)
+ struct itimerval *const value)
{
cputime_t cval, cinterval;
struct cpu_itimer *it = &tsk->signal->it[clock_id];
@@ -127,14 +127,32 @@ 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,
- struct itimerval *value, struct itimerval *ovalue)
+ const struct itimerval *const value,
+ struct itimerval *const ovalue)
{
- cputime_t cval, cinterval, nval, ninterval;
+ cputime_t cval, nval, cinterval, ninterval;
+ s64 ns_ninterval, ns_nval;
struct cpu_itimer *it = &tsk->signal->it[clock_id];
nval = timeval_to_cputime(&value->it_value);
+ ns_nval = timeval_to_ns(&value->it_value);
ninterval = timeval_to_cputime(&value->it_interval);
+ ns_ninterval = timeval_to_ns(&value->it_interval);
+
+ it->incr_error = cputime_sub_ns(ninterval, ns_ninterval);
+ it->error = cputime_sub_ns(nval, ns_nval);
spin_lock_irq(&tsk->sighand->siglock);
diff --git a/kernel/posix-cpu-timers.c b/kernel/posix-cpu-timers.c
index 9b2d5e4..b60d644 100644
--- a/kernel/posix-cpu-timers.c
+++ b/kernel/posix-cpu-timers.c
@@ -1070,6 +1070,8 @@ 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)
{
@@ -1077,9 +1079,16 @@ static void check_cpu_itimer(struct task_struct *tsk, struct cpu_itimer *it,
return;
if (cputime_ge(cur_time, it->expires)) {
- it->expires = it->incr;
- if (!cputime_eq(it->expires, cputime_zero))
- it->expires = cputime_add(it->expires, cur_time);
+ if (!cputime_eq(it->incr, cputime_zero)) {
+ it->expires = cputime_add(it->expires, it->incr);
+ it->error += it->incr_error;
+ if (it->error >= onecputick) {
+ it->expires = cputime_sub(it->expires,
+ jiffies_to_cputime(1));
+ it->error -= onecputick;
+ }
+ } else
+ it->expires = cputime_zero;
__group_send_sig_info(signo, SEND_SIG_PRIV, tsk);
}
@@ -1696,10 +1705,15 @@ static __init int init_posix_cpu_timers(void)
.nsleep = thread_cpu_nsleep,
.nsleep_restart = thread_cpu_nsleep_restart,
};
+ struct timespec ts;
register_posix_clock(CLOCK_PROCESS_CPUTIME_ID, &process);
register_posix_clock(CLOCK_THREAD_CPUTIME_ID, &thread);
+ cputime_to_timespec(jiffies_to_cputime(1), &ts);
+ onecputick = ts.tv_nsec;
+ WARN_ON(ts.tv_sec != 0);
+
return 0;
}
__initcall(init_posix_cpu_timers);