Commit ab0cce56 authored by Jiri Olsa's avatar Jiri Olsa Committed by Ingo Molnar
Browse files

Revert "sched, perf: Use a single callback into the scheduler" 



This reverts commit cb04ff9a ("sched, perf: Use a single
callback into the scheduler").

Before this change was introduced, the process switch worked
like this (wrt. to perf event schedule):

     schedule (prev, next)
       - schedule out all perf events for prev
       - switch to next
       - schedule in all perf events for current (next)

After the commit, the process switch looks like:

     schedule (prev, next)
       - schedule out all perf events for prev
       - schedule in all perf events for (next)
       - switch to next

The problem is, that after we schedule perf events in, the pmu
is enabled and we can receive events even before we make the
switch to next - so "current" still being prev process (event
SAMPLE data are filled based on the value of the "current"
process).

Thats exactly what we see for test__PERF_RECORD test. We receive
SAMPLES with PID of the process that our tracee is scheduled
from.

Discussed with Peter Zijlstra:

 > Bah!, yeah I guess reverting is the right thing for now. Sad
 > though.
 >
 > So by having the two hooks we have a black-spot between them
 > where we receive no events at all, this black-spot covers the
 > hand-over of current and we thus don't receive the 'wrong'
 > events.
 >
 > I rather liked we could do away with both that black-spot and
 > clean up the code a little, but apparently people rely on it.

Signed-off-by: default avatarJiri Olsa <jolsa@redhat.com>
Acked-by: default avatarPeter Zijlstra <a.p.zijlstra@chello.nl>
Cc: acme@redhat.com
Cc: paulus@samba.org
Cc: cjashfor@linux.vnet.ibm.com
Cc: fweisbec@gmail.com
Cc: eranian@google.com
Link: http://lkml.kernel.org/r/20120523111302.GC1638@m.brq.redhat.com


Signed-off-by: default avatarIngo Molnar <mingo@kernel.org>
parent 26252ea6

include/linux/perf_event.h

+18 −6
Original line number Diff line number Diff line
@@ -1084,7 +1084,9 @@ extern void perf_pmu_unregister(struct pmu *pmu); 


extern int perf_num_counters(void);

extern const char *perf_pmu_name(void);

extern void __perf_event_task_sched(struct task_struct *prev,

extern void __perf_event_task_sched_in(struct task_struct *prev,

				       struct task_struct *task);

extern void __perf_event_task_sched_out(struct task_struct *prev,

					struct task_struct *next);

extern int perf_event_init_task(struct task_struct *child);

extern void perf_event_exit_task(struct task_struct *child);
@@ -1205,13 +1207,20 @@ perf_sw_event(u32 event_id, u64 nr, struct pt_regs *regs, u64 addr) 


extern struct static_key_deferred perf_sched_events;



static inline void perf_event_task_sched(struct task_struct *prev,

static inline void perf_event_task_sched_in(struct task_struct *prev,

					    struct task_struct *task)

{

	if (static_key_false(&perf_sched_events.key))

		__perf_event_task_sched_in(prev, task);

}



static inline void perf_event_task_sched_out(struct task_struct *prev,

					     struct task_struct *next)

{

	perf_sw_event(PERF_COUNT_SW_CONTEXT_SWITCHES, 1, NULL, 0);



	if (static_key_false(&perf_sched_events.key))

		__perf_event_task_sched(prev, task);

		__perf_event_task_sched_out(prev, next);

}



extern void perf_event_mmap(struct vm_area_struct *vma);
@@ -1286,8 +1295,11 @@ extern void perf_event_disable(struct perf_event *event); 
extern void perf_event_task_tick(void);

#else

static inline void

perf_event_task_sched(struct task_struct *prev,

perf_event_task_sched_in(struct task_struct *prev,

			 struct task_struct *task)			{ }

static inline void

perf_event_task_sched_out(struct task_struct *prev,

			  struct task_struct *next)			{ }

static inline int perf_event_init_task(struct task_struct *child)	{ return 0; }

static inline void perf_event_exit_task(struct task_struct *child)	{ }

static inline void perf_event_free_task(struct task_struct *task)	{ }

kernel/events/core.c

+4 −10
Original line number Diff line number Diff line
@@ -2039,7 +2039,7 @@ static void perf_event_context_sched_out(struct task_struct *task, int ctxn, 
 * accessing the event control register. If a NMI hits, then it will

 * not restart the event.

 */

static void __perf_event_task_sched_out(struct task_struct *task,

void __perf_event_task_sched_out(struct task_struct *task,

				 struct task_struct *next)

{

	int ctxn;
@@ -2279,7 +2279,7 @@ static void perf_branch_stack_sched_in(struct task_struct *prev, 
 * accessing the event control register. If a NMI hits, then it will

 * keep the event running.

 */

static void __perf_event_task_sched_in(struct task_struct *prev,

void __perf_event_task_sched_in(struct task_struct *prev,

				struct task_struct *task)

{

	struct perf_event_context *ctx;
@@ -2305,12 +2305,6 @@ static void __perf_event_task_sched_in(struct task_struct *prev, 
		perf_branch_stack_sched_in(prev, task);

}



void __perf_event_task_sched(struct task_struct *prev, struct task_struct *next)

{

	__perf_event_task_sched_out(prev, next);

	__perf_event_task_sched_in(prev, next);

}



static u64 perf_calculate_period(struct perf_event *event, u64 nsec, u64 count)

{

	u64 frequency = event->attr.sample_freq;

kernel/sched/core.c

+8 −1
Original line number Diff line number Diff line
@@ -1913,7 +1913,7 @@ prepare_task_switch(struct rq *rq, struct task_struct *prev, 
		    struct task_struct *next)

{

	sched_info_switch(prev, next);

	perf_event_task_sched(prev, next);

	perf_event_task_sched_out(prev, next);

	fire_sched_out_preempt_notifiers(prev, next);

	prepare_lock_switch(rq, next);

	prepare_arch_switch(next);
@@ -1956,6 +1956,13 @@ static void finish_task_switch(struct rq *rq, struct task_struct *prev) 
	 */

	prev_state = prev->state;

	finish_arch_switch(prev);

#ifdef __ARCH_WANT_INTERRUPTS_ON_CTXSW

	local_irq_disable();

#endif /* __ARCH_WANT_INTERRUPTS_ON_CTXSW */

	perf_event_task_sched_in(prev, current);

#ifdef __ARCH_WANT_INTERRUPTS_ON_CTXSW

	local_irq_enable();

#endif /* __ARCH_WANT_INTERRUPTS_ON_CTXSW */

	finish_lock_switch(rq, prev);

	finish_arch_post_lock_switch();

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