Commit 6976675d authored by Arjan van de Ven's avatar Arjan van de Ven
Browse files

hrtimer: create a "timer_slack" field in the task struct 



We want to be able to control the default "rounding" that is used by
select() and poll() and friends. This is a per process property
(so that we can have a "nice" like program to start certain programs with
a looser or stricter rounding) that can be set/get via a prctl().

For this purpose, a field called "timer_slack_ns" is added to the task
struct. In addition, a field called "default_timer_slack"ns" is added
so that tasks easily can temporarily to a more/less accurate slack and then
back to the default.

The default value of the slack is set to 50 usec; this is significantly less
than 2.6.27's average select() and poll() timing error but still allows
the kernel to group timers somewhat to preserve power behavior. Applications
and admins can override this via the prctl()

Signed-off-by: default avatarArjan van de Ven <arjan@linux.intel.com>
parent 654c8e0b

include/linux/init_task.h

+1 −0
Original line number Diff line number Diff line
@@ -170,6 +170,7 @@ extern struct group_info init_groups; 
	.cpu_timers	= INIT_CPU_TIMERS(tsk.cpu_timers),		\

	.fs_excl	= ATOMIC_INIT(0),				\

	.pi_lock	= __SPIN_LOCK_UNLOCKED(tsk.pi_lock),		\

	.timer_slack_ns = 50000, /* 50 usec default slack */		\

	.pids = {							\

		[PIDTYPE_PID]  = INIT_PID_LINK(PIDTYPE_PID),		\

		[PIDTYPE_PGID] = INIT_PID_LINK(PIDTYPE_PGID),		\

include/linux/prctl.h

+7 −0
Original line number Diff line number Diff line
@@ -78,4 +78,11 @@ 
#define PR_GET_SECUREBITS 27

#define PR_SET_SECUREBITS 28



/*

 * Get/set the timerslack as used by poll/select/nanosleep

 * A value of 0 means "use default"

 */

#define PR_SET_TIMERSLACK 29

#define PR_GET_TIMERSLACK 30



#endif /* _LINUX_PRCTL_H */

include/linux/sched.h

+6 −0
Original line number Diff line number Diff line
@@ -1301,6 +1301,12 @@ struct task_struct { 
	int latency_record_count;

	struct latency_record latency_record[LT_SAVECOUNT];

#endif

	/*

	 * time slack values; these are used to round up poll() and

	 * select() etc timeout values. These are in nanoseconds.

	 */

	unsigned long timer_slack_ns;

	unsigned long default_timer_slack_ns;

};



/*

kernel/fork.c

+2 −0
Original line number Diff line number Diff line
@@ -987,6 +987,8 @@ static struct task_struct *copy_process(unsigned long clone_flags, 
	p->prev_utime = cputime_zero;

	p->prev_stime = cputime_zero;



	p->default_timer_slack_ns = current->timer_slack_ns;



#ifdef CONFIG_DETECT_SOFTLOCKUP

	p->last_switch_count = 0;

	p->last_switch_timestamp = 0;

kernel/sys.c

+10 −0
Original line number Diff line number Diff line
@@ -1727,6 +1727,16 @@ asmlinkage long sys_prctl(int option, unsigned long arg2, unsigned long arg3, 
		case PR_SET_TSC:

			error = SET_TSC_CTL(arg2);

			break;

		case PR_GET_TIMERSLACK:

			error = current->timer_slack_ns;

			break;

		case PR_SET_TIMERSLACK:

			if (arg2 <= 0)

				current->timer_slack_ns =

					current->default_timer_slack_ns;

			else

				current->timer_slack_ns = arg2;

			break;

		default:

			error = -EINVAL;

			break;

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