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Commit 6cd8a4bb authored by Steven Rostedt's avatar Steven Rostedt Committed by Thomas Gleixner
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ftrace: trace preempt off critical timings 



Add preempt off timings. A lot of kernel core code is taken from the RT patch
latency trace that was written by Ingo Molnar.

This adds "preemptoff" and "preemptirqsoff" to /debugfs/tracing/available_tracers

Now instead of just tracing irqs off, preemption off can be selected
to be recorded.

When this is selected, it shares the same files as irqs off timings.
One can either trace preemption off, irqs off, or one or the other off.

By echoing "preemptoff" into /debugfs/tracing/current_tracer, recording
of preempt off only is performed. "irqsoff" will only record the time
irqs are disabled, but "preemptirqsoff" will take the total time irqs
or preemption are disabled. Runtime switching of these options is now
supported by simpling echoing in the appropriate trace name into
/debugfs/tracing/current_tracer.

Signed-off-by: default avatarSteven Rostedt <srostedt@redhat.com>
Signed-off-by: default avatarIngo Molnar <mingo@elte.hu>
Signed-off-by: default avatarThomas Gleixner <tglx@linutronix.de>
parent 81d68a96

arch/x86/kernel/process_32.c

+3 −0
Original line number Diff line number Diff line
@@ -185,7 +185,10 @@ void cpu_idle(void) 


			local_irq_disable();

			__get_cpu_var(irq_stat).idle_timestamp = jiffies;

			/* Don't trace irqs off for idle */

			stop_critical_timings();

			idle();

			start_critical_timings();

		}

		tick_nohz_restart_sched_tick();

		preempt_enable_no_resched();

include/linux/ftrace.h

+8 −0
Original line number Diff line number Diff line
@@ -58,4 +58,12 @@ extern void mcount(void); 
# define time_hardirqs_off(a0, a1)		do { } while (0)

#endif



#ifdef CONFIG_PREEMPT_TRACER

  extern void notrace trace_preempt_on(unsigned long a0, unsigned long a1);

  extern void notrace trace_preempt_off(unsigned long a0, unsigned long a1);

#else

# define trace_preempt_on(a0, a1)		do { } while (0)

# define trace_preempt_off(a0, a1)		do { } while (0)

#endif



#endif /* _LINUX_FTRACE_H */

include/linux/irqflags.h

+2 −1
Original line number Diff line number Diff line
@@ -41,7 +41,8 @@ 
# define INIT_TRACE_IRQFLAGS

#endif



#ifdef CONFIG_IRQSOFF_TRACER

#if defined(CONFIG_IRQSOFF_TRACER) || \

	defined(CONFIG_PREEMPT_TRACER)

 extern void stop_critical_timings(void);

 extern void start_critical_timings(void);

#else

include/linux/preempt.h

+1 −1
Original line number Diff line number Diff line
@@ -10,7 +10,7 @@ 
#include <linux/linkage.h>

#include <linux/list.h>



#ifdef CONFIG_DEBUG_PREEMPT

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

  extern void add_preempt_count(int val);

  extern void sub_preempt_count(int val);

#else

kernel/sched.c

+23 −1
Original line number Diff line number Diff line
@@ -70,6 +70,7 @@ 
#include <linux/bootmem.h>

#include <linux/debugfs.h>

#include <linux/ctype.h>

#include <linux/ftrace.h>



#include <asm/tlb.h>

#include <asm/irq_regs.h>
@@ -4365,26 +4366,44 @@ void scheduler_tick(void) 
#endif

}



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

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

				defined(CONFIG_PREEMPT_TRACER))



static inline unsigned long get_parent_ip(unsigned long addr)

{

	if (in_lock_functions(addr)) {

		addr = CALLER_ADDR2;

		if (in_lock_functions(addr))

			addr = CALLER_ADDR3;

	}

	return addr;

}



void __kprobes add_preempt_count(int val)

{

#ifdef CONFIG_DEBUG_PREEMPT

	/*

	 * Underflow?

	 */

	if (DEBUG_LOCKS_WARN_ON((preempt_count() < 0)))

		return;

#endif

	preempt_count() += val;

#ifdef CONFIG_DEBUG_PREEMPT

	/*

	 * Spinlock count overflowing soon?

	 */

	DEBUG_LOCKS_WARN_ON((preempt_count() & PREEMPT_MASK) >=

				PREEMPT_MASK - 10);

#endif

	if (preempt_count() == val)

		trace_preempt_off(CALLER_ADDR0, get_parent_ip(CALLER_ADDR1));

}

EXPORT_SYMBOL(add_preempt_count);



void __kprobes sub_preempt_count(int val)

{

#ifdef CONFIG_DEBUG_PREEMPT

	/*

	 * Underflow?

	 */
@@ -4396,7 +4415,10 @@ void __kprobes sub_preempt_count(int val) 
	if (DEBUG_LOCKS_WARN_ON((val < PREEMPT_MASK) &&

			!(preempt_count() & PREEMPT_MASK)))

		return;

#endif



	if (preempt_count() == val)

		trace_preempt_on(CALLER_ADDR0, get_parent_ip(CALLER_ADDR1));

	preempt_count() -= val;

}

EXPORT_SYMBOL(sub_preempt_count);