Commit 8356b5f9 authored by Stanislaw Gruszka's avatar Stanislaw Gruszka Committed by Ingo Molnar
Browse files

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: default avatarStanislaw Gruszka <sgruszka@redhat.com>
Acked-by: default avatarPeter Zijlstra <a.p.zijlstra@chello.nl>
Acked-by: default avatarThomas 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: default avatarIngo Molnar <mingo@elte.hu>
parent 42c4ab41

include/linux/sched.h

+2 −0
Original line number Diff line number Diff line
@@ -473,6 +473,8 @@ struct pacct_struct { 
struct cpu_itimer {

	cputime_t expires;

	cputime_t incr;

	u32 error;

	u32 incr_error;

};



/**

kernel/itimer.c

+21 −3
Original line number Diff line number Diff line
@@ -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);

kernel/posix-cpu-timers.c

+17 −3
Original line number Diff line number Diff line
@@ -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);

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