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Commit fd6298c8 authored by Pavankumar Kondeti's avatar Pavankumar Kondeti
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tracing: rework sched_preempt_disable trace point implementation 



The current implementation of sched_preempt_disable trace point
fails to detect the preemption disable time inside spin_lock_bh()
and spin_unlock_bh(). This is because __local_bh_disable_ip() calls
directly __preempt_count_add() which skips the preemption disable
tracking. Instead of relying on the updates to preempt count, it
is better to write the preemption disable tracking directly to
preemptsoff tracer. This is similar to how irq disable tracking
is done.

The current code handles the false positives coming from __schedule()
by directly resetting the time stamp. This requires an interface
from the scheduler to preemptsoff tracer. To avoid this additional
interface, the current patch detects the same condition by comparing
the task pid and context switch count. If they are not matching
at the time of preemption disable to enable, don't track the preemption
disable time as it involved a context switch.

Due to this rework. the sched_preempt_disable trace point location is
changed to

/sys/kernel/debug/tracing/events/preemptirq/sched_preempt_disable/enable

Change-Id: I7f58d316b7c54bc7a54102bfeb678404bda010d4
Signed-off-by: default avatarPavankumar Kondeti <pkondeti@codeaurora.org>
parent 5e3f09ce

include/linux/sched/sysctl.h

+1 −1
Original line number Diff line number Diff line
@@ -76,7 +76,7 @@ extern int sched_updown_migrate_handler(struct ctl_table *table, 
					size_t *lenp, loff_t *ppos);

#endif



#if defined(CONFIG_PREEMPT_TRACER) || defined(CONFIG_DEBUG_PREEMPT)

#if defined(CONFIG_PREEMPTIRQ_EVENTS) || defined(CONFIG_PREEMPT_TRACER)

extern unsigned int sysctl_preemptoff_tracing_threshold_ns;

#endif

#if defined(CONFIG_PREEMPTIRQ_EVENTS) && defined(CONFIG_IRQSOFF_TRACER)

include/trace/events/preemptirq.h

+32 −0
Original line number Diff line number Diff line
@@ -90,6 +90,38 @@ TRACE_EVENT(irqs_disable, 
					__entry->caddr2, __entry->caddr3)

);



TRACE_EVENT(sched_preempt_disable,



	TP_PROTO(u64 delta, bool irqs_disabled,

			unsigned long caddr0, unsigned long caddr1,

			unsigned long caddr2, unsigned long caddr3),



	TP_ARGS(delta, irqs_disabled, caddr0, caddr1, caddr2, caddr3),



	TP_STRUCT__entry(

		__field(u64, delta)

		__field(bool, irqs_disabled)

		__field(void*, caddr0)

		__field(void*, caddr1)

		__field(void*, caddr2)

		__field(void*, caddr3)

	),



	TP_fast_assign(

		__entry->delta = delta;

		__entry->irqs_disabled = irqs_disabled;

		__entry->caddr0 = (void *)caddr0;

		__entry->caddr1 = (void *)caddr1;

		__entry->caddr2 = (void *)caddr2;

		__entry->caddr3 = (void *)caddr3;

	),



	TP_printk("delta=%llu(ns) irqs_d=%d Callers:(%ps<-%ps<-%ps<-%ps)",

				__entry->delta, __entry->irqs_disabled,

				__entry->caddr0, __entry->caddr1,

				__entry->caddr2, __entry->caddr3)

);



#endif /* _TRACE_PREEMPTIRQ_H */



#include <trace/define_trace.h>

include/trace/events/sched.h

+0 −32
Original line number Diff line number Diff line
@@ -1649,38 +1649,6 @@ TRACE_EVENT(sched_isolate, 
		__entry->time, __entry->isolate)

);



TRACE_EVENT(sched_preempt_disable,



	TP_PROTO(u64 delta, bool irqs_disabled,

			unsigned long caddr0, unsigned long caddr1,

			unsigned long caddr2, unsigned long caddr3),



	TP_ARGS(delta, irqs_disabled, caddr0, caddr1, caddr2, caddr3),



	TP_STRUCT__entry(

		__field(u64, delta)

		__field(bool, irqs_disabled)

		__field(void*, caddr0)

		__field(void*, caddr1)

		__field(void*, caddr2)

		__field(void*, caddr3)

	),



	TP_fast_assign(

		__entry->delta = delta;

		__entry->irqs_disabled = irqs_disabled;

		__entry->caddr0 = (void *)caddr0;

		__entry->caddr1 = (void *)caddr1;

		__entry->caddr2 = (void *)caddr2;

		__entry->caddr3 = (void *)caddr3;

	),



	TP_printk("delta=%llu(ns) irqs_d=%d Callers:(%ps<-%ps<-%ps<-%ps)",

				__entry->delta, __entry->irqs_disabled,

				__entry->caddr0, __entry->caddr1,

				__entry->caddr2, __entry->caddr3)

);



#include "walt.h"

#endif /* CONFIG_SMP */

#endif /* _TRACE_SCHED_H */

kernel/sched/core.c

+0 −53
Original line number Diff line number Diff line
@@ -3353,55 +3353,17 @@ static inline void sched_tick_stop(int cpu) { } 


#if defined(CONFIG_PREEMPT) && (defined(CONFIG_DEBUG_PREEMPT) || \

				defined(CONFIG_TRACE_PREEMPT_TOGGLE))

/*

 * preemptoff stack tracing threshold in ns.

 * default: 1ms

 */

unsigned int sysctl_preemptoff_tracing_threshold_ns = 1000000UL;



struct preempt_store {

	u64 ts;

	unsigned long caddr[4];

	bool irqs_disabled;

};



DEFINE_PER_CPU(struct preempt_store, the_ps);



/*

 * This is only called from __schedule() upon context switch.

 *

 * schedule() calls __schedule() with preemption disabled.

 * if we had entered idle and exiting idle now, reset the preemption

 * tracking otherwise we may think preemption is disabled the whole time

 * when the non idle task re-enables the preemption in schedule().

 */

static inline void preempt_latency_reset(void)

{

	if (is_idle_task(this_rq()->curr))

		this_cpu_ptr(&the_ps)->ts = 0;

}



/*

 * If the value passed in is equal to the current preempt count

 * then we just disabled preemption. Start timing the latency.

 */

static inline void preempt_latency_start(int val)

{

	int cpu = raw_smp_processor_id();

	struct preempt_store *ps = &per_cpu(the_ps, cpu);



	if (preempt_count() == val) {

		unsigned long ip = get_lock_parent_ip();

#ifdef CONFIG_DEBUG_PREEMPT

		current->preempt_disable_ip = ip;

#endif

		ps->ts = sched_clock();

		ps->caddr[0] = CALLER_ADDR0;

		ps->caddr[1] = CALLER_ADDR1;

		ps->caddr[2] = CALLER_ADDR2;

		ps->caddr[3] = CALLER_ADDR3;

		ps->irqs_disabled = irqs_disabled();



		trace_preempt_off(CALLER_ADDR0, ip);

	}

}
@@ -3435,19 +3397,6 @@ NOKPROBE_SYMBOL(preempt_count_add); 
static inline void preempt_latency_stop(int val)

{

	if (preempt_count() == val) {

		struct preempt_store *ps = &per_cpu(the_ps,

				raw_smp_processor_id());

		u64 delta = ps->ts ? (sched_clock() - ps->ts) : 0;



		/*

		 * Trace preempt disable stack if preemption

		 * is disabled for more than the threshold.

		 */

		if (delta > sysctl_preemptoff_tracing_threshold_ns)

			trace_sched_preempt_disable(delta, ps->irqs_disabled,

						ps->caddr[0], ps->caddr[1],

						ps->caddr[2], ps->caddr[3]);

		ps->ts = 0;

		trace_preempt_on(CALLER_ADDR0, get_lock_parent_ip());

	}

}
@@ -3477,7 +3426,6 @@ NOKPROBE_SYMBOL(preempt_count_sub); 
#else

static inline void preempt_latency_start(int val) { }

static inline void preempt_latency_stop(int val) { }

static inline void preempt_latency_reset(void) { }

#endif



static inline unsigned long get_preempt_disable_ip(struct task_struct *p)
@@ -3701,7 +3649,6 @@ static void __sched notrace __schedule(bool preempt) 
		if (!prev->on_rq)

			prev->last_sleep_ts = wallclock;



		preempt_latency_reset();

		update_task_ravg(prev, rq, PUT_PREV_TASK, wallclock, 0);

		update_task_ravg(next, rq, PICK_NEXT_TASK, wallclock, 0);

		rq->nr_switches++;

kernel/sysctl.c

+1 −1
Original line number Diff line number Diff line
@@ -336,7 +336,7 @@ static struct ctl_table kern_table[] = { 
		.mode		= 0644,

		.proc_handler	= proc_dointvec,

	},

#if defined(CONFIG_PREEMPT_TRACER) || defined(CONFIG_DEBUG_PREEMPT)

#if defined(CONFIG_PREEMPT_TRACER) && defined(CONFIG_PREEMPTIRQ_EVENTS)

	{

		.procname       = "preemptoff_tracing_threshold_ns",

		.data           = &sysctl_preemptoff_tracing_threshold_ns,