Measure latencies caused due to delayed timer offsets in nanoseconds. It shows the latency captured due to a delayed timer expire event. It happens for example when a timer misses its deadline due to disabled interrupts. A process if scheduled as a result of the timer expiration suffers this latency. It is used to calculate the total wakeup latency of a process which is the sum of the delayed timer offset and the wakeup latency.
[ Initial work and idea by Carsten Link: https://git.kernel.org/cgit/linux/kernel/git/rt/linux-stable-rt.git/commit/?h=v3.14-rt-rebase&id=56d50cc34943bbba12b8c5942ee1ae3b29f73acb ] Cc: Carsten Emde <c.e...@osadl.org> Signed-off-by: Binoy Jayan <binoy.ja...@linaro.org> --- include/linux/hrtimer.h | 4 ++++ include/linux/sched.h | 3 +++ kernel/time/Kconfig | 8 ++++++++ kernel/time/hrtimer.c | 47 +++++++++++++++++++++++++++++++++++++++++++++++ 4 files changed, 62 insertions(+) diff --git a/include/linux/hrtimer.h b/include/linux/hrtimer.h index 5e00f80..05d8086 100644 --- a/include/linux/hrtimer.h +++ b/include/linux/hrtimer.h @@ -90,6 +90,7 @@ enum hrtimer_restart { * @is_rel: Set if the timer was armed relative * @start_pid: timer statistics field to store the pid of the task which * started the timer + * @tim_expiry: hrtimer expiry time or 0 in case already expired * @start_site: timer statistics field to store the site where the timer * was started * @start_comm: timer statistics field to store the name of the process which @@ -104,6 +105,9 @@ struct hrtimer { struct hrtimer_clock_base *base; u8 state; u8 is_rel; +#ifdef CONFIG_TRACE_DELAYED_TIMER_OFFSETS + ktime_t tim_expiry; +#endif #ifdef CONFIG_TIMER_STATS int start_pid; void *start_site; diff --git a/include/linux/sched.h b/include/linux/sched.h index 62c68e5..7bf67f8 100644 --- a/include/linux/sched.h +++ b/include/linux/sched.h @@ -1891,6 +1891,9 @@ struct task_struct { /* bitmask and counter of trace recursion */ unsigned long trace_recursion; #endif /* CONFIG_TRACING */ +#ifdef CONFIG_TRACE_DELAYED_TIMER_OFFSETS + long timer_offset; +#endif /* CONFIG_TRACE_DELAYED_TIMER_OFFSETS */ #ifdef CONFIG_KCOV /* Coverage collection mode enabled for this task (0 if disabled). */ enum kcov_mode kcov_mode; diff --git a/kernel/time/Kconfig b/kernel/time/Kconfig index 4008d9f..de4793c 100644 --- a/kernel/time/Kconfig +++ b/kernel/time/Kconfig @@ -193,5 +193,13 @@ config HIGH_RES_TIMERS hardware is not capable then this option only increases the size of the kernel image. +config TRACE_DELAYED_TIMER_OFFSETS + depends on HIGH_RES_TIMERS + select GENERIC_TRACER + bool "Delayed Timer Offsets" + help + Capture offsets of delayed hrtimer in nanoseconds. It is used + to construct wakeup latency histogram. + endmenu endif diff --git a/kernel/time/hrtimer.c b/kernel/time/hrtimer.c index 9ba7c82..7048f86 100644 --- a/kernel/time/hrtimer.c +++ b/kernel/time/hrtimer.c @@ -56,6 +56,8 @@ #include "tick-internal.h" +static enum hrtimer_restart hrtimer_wakeup(struct hrtimer *timer); + /* * The timer bases: * @@ -960,6 +962,47 @@ static inline ktime_t hrtimer_update_lowres(struct hrtimer *timer, ktime_t tim, return tim; } +#ifdef CONFIG_TRACE_DELAYED_TIMER_OFFSETS +static inline void latency_hrtimer_timing_start(struct hrtimer *timer, + struct hrtimer_clock_base *new_base, + ktime_t tim) +{ + ktime_t now = new_base->get_time(); + + if (ktime_to_ns(tim) < ktime_to_ns(now)) + timer->tim_expiry = now; + else + timer->tim_expiry = ktime_set(0, 0); +} + +static inline void latency_hrtimer_timing_stop(struct hrtimer *timer, + ktime_t basenow) +{ + long latency; + struct task_struct *task; + + latency = ktime_to_ns(ktime_sub(basenow, + ktime_to_ns(timer->tim_expiry) ? + timer->tim_expiry : hrtimer_get_expires(timer))); + task = timer->function == hrtimer_wakeup ? + container_of(timer, struct hrtimer_sleeper, + timer)->task : NULL; + if (task && latency > 0) + task->timer_offset = latency; +} +#else +static inline void latency_hrtimer_timing_start(struct hrtimer *timer, + struct hrtimer_clock_base *new_base, + ktime_t tim) +{ +} +static inline void latency_hrtimer_timing_stop(struct hrtimer *timer, + ktime_t basenow) +{ +} + +#endif + /** * hrtimer_start_range_ns - (re)start an hrtimer on the current CPU * @timer: the timer to be added @@ -992,6 +1035,8 @@ void hrtimer_start_range_ns(struct hrtimer *timer, ktime_t tim, timer_stats_hrtimer_set_start_info(timer); + latency_hrtimer_timing_start(timer, new_base, tim); + leftmost = enqueue_hrtimer(timer, new_base); if (!leftmost) goto unlock; @@ -1284,6 +1329,8 @@ static void __hrtimer_run_queues(struct hrtimer_cpu_base *cpu_base, ktime_t now) timer = container_of(node, struct hrtimer, node); + latency_hrtimer_timing_stop(timer, basenow); + /* * The immediate goal for using the softexpires is * minimizing wakeups, not running timers at the -- The Qualcomm Innovation Center, Inc. is a member of the Code Aurora Forum, a Linux Foundation Collaborative Project
