This patch proposes a system-wide sysctl-aware default for the high-resolution timer slack value, which may be changed from 0 to HRTIMER_MAX_SLACK nanoseconds. Default system-wide and per-task values are HRTIMER_DEFAULT_SLACK. Per-task value isn't inherited across fork(); instead, newborn task uses system-wide value by default, and newborn thread uses it's group leader value.
Signed-off-by: Dmitry Antipov dmitry.antipov@linaro.org --- Documentation/sysctl/kernel.txt | 8 ++++++++ include/linux/hrtimer.h | 11 +++++++++++ include/linux/init_task.h | 2 +- include/linux/sched.h | 11 ++++++++--- kernel/fork.c | 9 +++++++-- kernel/futex.c | 4 ++-- kernel/hrtimer.c | 10 +++++++--- kernel/sys.c | 9 ++++----- kernel/sysctl.c | 10 ++++++++++ 9 files changed, 58 insertions(+), 16 deletions(-)
diff --git a/Documentation/sysctl/kernel.txt b/Documentation/sysctl/kernel.txt index 6d78841..83b63ed 100644 --- a/Documentation/sysctl/kernel.txt +++ b/Documentation/sysctl/kernel.txt @@ -606,6 +606,14 @@ can be ORed together:
==============================================================
+timer_slack: + +This value can be used to query and set the default slack for +high-resolution timers, in nanoseconds. The default value is 50 +microseconds, and can be changed from 0 nanoseconds to 1 millisecond. + +============================================================== + unknown_nmi_panic:
The value in this file affects behavior of handling NMI. When the diff --git a/include/linux/hrtimer.h b/include/linux/hrtimer.h index fd0dc30..77169b7 100644 --- a/include/linux/hrtimer.h +++ b/include/linux/hrtimer.h @@ -24,6 +24,16 @@ #include <linux/timer.h> #include <linux/timerqueue.h>
+/* + * Default system-wide and per-task hrtimer slack, in nanoseconds. + */ +#define HRTIMER_DEFAULT_SLACK 50000 + +/* + * Reasonable limit for hrtimer slack. + */ +#define HRTIMER_MAX_SLACK 1000000 + struct hrtimer_clock_base; struct hrtimer_cpu_base;
@@ -323,6 +333,7 @@ extern ktime_t ktime_get_monotonic_offset(void);
DECLARE_PER_CPU(struct tick_device, tick_cpu_device);
+extern int default_timer_slack_ns;
/* Exported timer functions: */
diff --git a/include/linux/init_task.h b/include/linux/init_task.h index 9c66b1a..b29be0d 100644 --- a/include/linux/init_task.h +++ b/include/linux/init_task.h @@ -178,7 +178,7 @@ extern struct cred init_cred; .journal_info = NULL, \ .cpu_timers = INIT_CPU_TIMERS(tsk.cpu_timers), \ .pi_lock = __RAW_SPIN_LOCK_UNLOCKED(tsk.pi_lock), \ - .timer_slack_ns = 50000, /* 50 usec default slack */ \ + .timer_slack_ns = HRTIMER_DEFAULT_SLACK, \ .pids = { \ [PIDTYPE_PID] = INIT_PID_LINK(PIDTYPE_PID), \ [PIDTYPE_PGID] = INIT_PID_LINK(PIDTYPE_PGID), \ diff --git a/include/linux/sched.h b/include/linux/sched.h index 9b13f79..811e034 100644 --- a/include/linux/sched.h +++ b/include/linux/sched.h @@ -1551,11 +1551,11 @@ struct task_struct { 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. + * High-resolution timer slack value, in nanoseconds. + * Used to round up poll()/select(), nanosleep, futex + * waiting, etc. timeout values of non-realtime tasks. */ unsigned long timer_slack_ns; - unsigned long default_timer_slack_ns;
struct list_head *scm_work_list; #ifdef CONFIG_FUNCTION_GRAPH_TRACER @@ -2631,6 +2631,11 @@ static inline int spin_needbreak(spinlock_t *lock) #endif }
+static inline unsigned long task_timer_slack(struct task_struct *tsk) +{ + return rt_task(tsk) ? 0 : tsk->timer_slack_ns; +} + /* * Thread group CPU time accounting. */ diff --git a/kernel/fork.c b/kernel/fork.c index b77fd55..6aaff93 100644 --- a/kernel/fork.c +++ b/kernel/fork.c @@ -1164,8 +1164,13 @@ static struct task_struct *copy_process(unsigned long clone_flags, #if defined(SPLIT_RSS_COUNTING) memset(&p->rss_stat, 0, sizeof(p->rss_stat)); #endif - - p->default_timer_slack_ns = current->timer_slack_ns; + /* + * New thread inherits the slack from the group + * leader. New process uses system-default slack. + */ + p->timer_slack_ns = (clone_flags & CLONE_THREAD) ? + current->group_leader->timer_slack_ns : + default_timer_slack_ns;
task_io_accounting_init(&p->ioac); acct_clear_integrals(p); diff --git a/kernel/futex.c b/kernel/futex.c index 1614be2..a0d302d 100644 --- a/kernel/futex.c +++ b/kernel/futex.c @@ -1887,7 +1887,7 @@ static int futex_wait(u32 __user *uaddr, unsigned int flags, u32 val, HRTIMER_MODE_ABS); hrtimer_init_sleeper(to, current); hrtimer_set_expires_range_ns(&to->timer, *abs_time, - current->timer_slack_ns); + task_timer_slack(current)); }
retry: @@ -2281,7 +2281,7 @@ static int futex_wait_requeue_pi(u32 __user *uaddr, unsigned int flags, HRTIMER_MODE_ABS); hrtimer_init_sleeper(to, current); hrtimer_set_expires_range_ns(&to->timer, *abs_time, - current->timer_slack_ns); + task_timer_slack(current)); }
/* diff --git a/kernel/hrtimer.c b/kernel/hrtimer.c index ae34bf5..0c56fec 100644 --- a/kernel/hrtimer.c +++ b/kernel/hrtimer.c @@ -51,6 +51,12 @@ #include <trace/events/timer.h>
/* + * Default hrtimer slack value, in nanoseconds. May be changed in + * [0..HRTIMER_MAX_SLACK] range through kernel.timer_slack sysctl. + */ +__read_mostly int default_timer_slack_ns = HRTIMER_DEFAULT_SLACK; + +/* * The timer bases: * * There are more clockids then hrtimer bases. Thus, we index @@ -1564,9 +1570,7 @@ long hrtimer_nanosleep(struct timespec *rqtp, struct timespec __user *rmtp, int ret = 0; unsigned long slack;
- slack = current->timer_slack_ns; - if (rt_task(current)) - slack = 0; + slack = task_timer_slack(current);
hrtimer_init_on_stack(&t.timer, clockid, mode); hrtimer_set_expires_range_ns(&t.timer, timespec_to_ktime(*rqtp), slack); diff --git a/kernel/sys.c b/kernel/sys.c index 4070153..ac32846 100644 --- a/kernel/sys.c +++ b/kernel/sys.c @@ -22,6 +22,7 @@ #include <linux/device.h> #include <linux/key.h> #include <linux/times.h> +#include <linux/hrtimer.h> #include <linux/posix-timers.h> #include <linux/security.h> #include <linux/dcookies.h> @@ -1917,12 +1918,10 @@ SYSCALL_DEFINE5(prctl, int, option, unsigned long, arg2, unsigned long, arg3, error = current->timer_slack_ns; break; case PR_SET_TIMERSLACK: - if (arg2 <= 0) - current->timer_slack_ns = - current->default_timer_slack_ns; - else + if (arg2 <= HRTIMER_MAX_SLACK) current->timer_slack_ns = arg2; - error = 0; + else + error = -EINVAL; break; case PR_MCE_KILL: if (arg4 | arg5) diff --git a/kernel/sysctl.c b/kernel/sysctl.c index f487f25..2cd42c6 100644 --- a/kernel/sysctl.c +++ b/kernel/sysctl.c @@ -136,6 +136,7 @@ static int min_percpu_pagelist_fract = 8;
static int ngroups_max = NGROUPS_MAX; static const int cap_last_cap = CAP_LAST_CAP; +static const int slack_max = HRTIMER_MAX_SLACK;
#ifdef CONFIG_INOTIFY_USER #include <linux/inotify.h> @@ -1004,6 +1005,15 @@ static struct ctl_table kern_table[] = { .proc_handler = proc_dointvec, }, #endif + { + .procname = "timer_slack", + .data = &default_timer_slack_ns, + .maxlen = sizeof(int), + .mode = 0644, + .proc_handler = proc_dointvec_minmax, + .extra1 = &zero, + .extra2 = &slack_max, + }, { } };