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perf: Fix software migrate events

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Stephane asked about PERF_COUNT_SW_CPU_MIGRATIONS and I realized it
was borken:

 > The problem is that the task isn't actually scheduled while its being
 > migrated (obviously), and if its not scheduled, the counters aren't
 > scheduled either, so there's no observing of the fact.
 >
 > A further problem with migrations is that many migrations happen from
 > softirq context, which is nested inside the 'random' task context of
 > whoemever happens to run at that time, similarly for the wakeup
 > migrations triggered from (soft)irq context. All those end up being
 > accounted in the task that's currently running, eg. your 'ls'.

The below cures this by marking a task as migrated and accounting it
on the subsequent sched_in().

Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: Borislav Petkov <bp@alien8.de>
Cc: H. Peter Anvin <hpa@zytor.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Stephane Eranian <eranian@google.com>
Cc: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: Ingo Molnar <mingo@kernel.org>
This commit is contained in:
Peter Zijlstra
2015-04-17 20:05:30 +02:00
committed by Ingo Molnar
parent 1836ac856e
commit ff303e66c2
3 changed files with 29 additions and 4 deletions
Download Patch File Download Diff File Expand all files Collapse all files

24
include/linux/perf_event.h
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@@ -798,11 +798,33 @@ perf_sw_event_sched(u32 event_id, u64 nr, u64 addr)
extern struct static_key_deferred perf_sched_events;
static __always_inline bool
perf_sw_migrate_enabled(void)
{
if (static_key_false(&perf_swevent_enabled[PERF_COUNT_SW_CPU_MIGRATIONS]))
return true;
return false;
}
static inline void perf_event_task_migrate(struct task_struct *task)
{
if (perf_sw_migrate_enabled())
task->sched_migrated = 1;
}
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);
if (perf_sw_migrate_enabled() && task->sched_migrated) {
struct pt_regs *regs = this_cpu_ptr(&__perf_regs[0]);
perf_fetch_caller_regs(regs);
___perf_sw_event(PERF_COUNT_SW_CPU_MIGRATIONS, 1, regs, 0);
task->sched_migrated = 0;
}
}
static inline void perf_event_task_sched_out(struct task_struct *prev,
@@ -925,6 +947,8 @@ perf_aux_output_skip(struct perf_output_handle *handle,
static inline void *
perf_get_aux(struct perf_output_handle *handle) { return NULL; }
static inline void
perf_event_task_migrate(struct task_struct *task) { }
static inline void
perf_event_task_sched_in(struct task_struct *prev,
struct task_struct *task) { }
static inline void