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Subject[PATCH, v10 1/3] hrtimer: introduce effective timer slack
Date
From: "Kirill A. Shutemov" <kirill@shutemov.name>

task_get_effective_timer_slack() returns timer slack value to be used
to configure per-task timers. It can be equal or higher than task's
timer slack value.

For now task_get_effective_timer_slack() returns timer_slack_ns of the
task. Timer slack cgroup controller will implement a bit more
sophisticated logic.

Signed-off-by: Kirill A. Shutemov <kirill@shutemov.name>
---
fs/select.c | 7 ++-----
include/linux/sched.h | 6 ++++++
kernel/fork.c | 4 ++++
kernel/futex.c | 4 ++--
kernel/hrtimer.c | 2 +-
5 files changed, 15 insertions(+), 8 deletions(-)

diff --git a/fs/select.c b/fs/select.c
index b6765cf..c6eb8fa 100644
--- a/fs/select.c
+++ b/fs/select.c
@@ -69,7 +69,6 @@ static long __estimate_accuracy(struct timespec *tv)

long select_estimate_accuracy(struct timespec *tv)
{
- unsigned long ret;
struct timespec now;

/*
@@ -81,10 +80,8 @@ long select_estimate_accuracy(struct timespec *tv)

ktime_get_ts(&now);
now = timespec_sub(*tv, now);
- ret = __estimate_accuracy(&now);
- if (ret < current->timer_slack_ns)
- return current->timer_slack_ns;
- return ret;
+ return min_t(long, __estimate_accuracy(&now),
+ task_get_effective_timer_slack(current));
}


diff --git a/include/linux/sched.h b/include/linux/sched.h
index 28edc96..d79e300 100644
--- a/include/linux/sched.h
+++ b/include/linux/sched.h
@@ -2719,6 +2719,12 @@ static inline unsigned long rlimit_max(unsigned int limit)
return task_rlimit_max(current, limit);
}

+static inline unsigned long task_get_effective_timer_slack(
+ struct task_struct *tsk)
+{
+ return tsk->timer_slack_ns;
+}
+
#endif /* __KERNEL__ */

#endif
diff --git a/kernel/fork.c b/kernel/fork.c
index 0675082..4a9fd53 100644
--- a/kernel/fork.c
+++ b/kernel/fork.c
@@ -1180,6 +1180,10 @@ static struct task_struct *copy_process(unsigned long clone_flags,
memset(&p->rss_stat, 0, sizeof(p->rss_stat));
#endif

+ /*
+ * Save current task's (not effective) timer slack value as default
+ * timer slack value for new task.
+ */
p->default_timer_slack_ns = current->timer_slack_ns;

task_io_accounting_init(&p->ioac);
diff --git a/kernel/futex.c b/kernel/futex.c
index ea87f4d..14f04b9 100644
--- a/kernel/futex.c
+++ b/kernel/futex.c
@@ -1875,7 +1875,7 @@ 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_get_effective_timer_slack(current));
}

retry:
@@ -2269,7 +2269,7 @@ 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_get_effective_timer_slack(current));
}

/*
diff --git a/kernel/hrtimer.c b/kernel/hrtimer.c
index 422e567..379460b 100644
--- a/kernel/hrtimer.c
+++ b/kernel/hrtimer.c
@@ -1562,7 +1562,7 @@ long hrtimer_nanosleep(struct timespec *rqtp, struct timespec __user *rmtp,
int ret = 0;
unsigned long slack;

- slack = current->timer_slack_ns;
+ slack = task_get_effective_timer_slack(current);
if (rt_task(current))
slack = 0;

--
1.7.6.3


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