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Message-ID: <CAHLCerPMLLp+YPiFmQrv1qpUF3EC7Fkdf2x0U+LE8YO21spKug@mail.gmail.com>
Date: Fri, 27 Jan 2012 13:50:10 +0200
From: Amit Kucheria <amit.kucheria@...durent.com>
To: Dmitry Antipov <dmitry.antipov@...aro.org>
Cc: Thomas Gleixner <tglx@...utronix.de>,
John Stultz <john.stultz@...aro.org>,
linux-kernel@...r.kernel.org, patches@...aro.org,
linaro-dev@...ts.linaro.org
Subject: Re: [PATCH] hrtimers: move default_timer_slack_ns to system-wide sysctl
Dmitry,
On Fri, Jan 27, 2012 at 12:30 PM, Dmitry Antipov
<dmitry.antipov@...aro.org> wrote:
> - moving default_timer_slack_ns from per-task field to global variable
> controlled via sysctl() in [0..1000000] range (usecs) provides some
> more system-wide control beyond per-task prctl();
What benefits do I get from this change? In other words, don't just
describe the change, please describe why it is desirable.
Have you done any tests where this improves things - reduction in
wakeups, increase in throughput? Those results will also help in
getting more attention on the patch.
> - task_time_slack() should be used to get default timer slack if no
> special requirements exists.
>
> Signed-off-by: Dmitry Antipov <dmitry.antipov@...aro.org>
> ---
> include/linux/hrtimer.h | 1 +
> include/linux/sched.h | 11 ++++++++---
> kernel/fork.c | 3 ---
> kernel/futex.c | 4 ++--
> kernel/hrtimer.c | 10 +++++++---
> kernel/sys.c | 3 ++-
> kernel/sysctl.c | 10 ++++++++++
> 7 files changed, 30 insertions(+), 12 deletions(-)
>
> diff --git a/include/linux/hrtimer.h b/include/linux/hrtimer.h
> index fd0dc30..855d45e 100644
> --- a/include/linux/hrtimer.h
> +++ b/include/linux/hrtimer.h
> @@ -323,6 +323,7 @@ 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/sched.h b/include/linux/sched.h
> index 2234985..4f475aa 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 for 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
> @@ -2622,6 +2622,11 @@ 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 051f090..b0e8f63 100644
> --- a/kernel/fork.c
> +++ b/kernel/fork.c
> @@ -1144,9 +1144,6 @@ 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;
> -
> 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..0704559 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 via sysctl within [0..1000000] range.
> + */
> +int default_timer_slack_ns = 50000;
> +
> +/*
> * 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..db36543 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>
> @@ -1919,7 +1920,7 @@ SYSCALL_DEFINE5(prctl, int, option, unsigned long, arg2, unsigned long, arg3,
> case PR_SET_TIMERSLACK:
> if (arg2 <= 0)
> current->timer_slack_ns =
> - current->default_timer_slack_ns;
> + default_timer_slack_ns;
> else
> current->timer_slack_ns = arg2;
> error = 0;
> diff --git a/kernel/sysctl.c b/kernel/sysctl.c
> index f487f25..c9a731b 100644
> --- a/kernel/sysctl.c
> +++ b/kernel/sysctl.c
> @@ -122,6 +122,7 @@ static int __maybe_unused two = 2;
> static int __maybe_unused three = 3;
> static unsigned long one_ul = 1;
> static int one_hundred = 100;
> +static int million = 1000000;
> #ifdef CONFIG_PRINTK
> static int ten_thousand = 10000;
> #endif
> @@ -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 = &million,
> + },
> { }
> };
>
> --
> 1.7.7.5
>
> --
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