Commit-ID: ff303e66c240ba6269e31817a386995440a18c99
Gitweb: http://git.kernel.org/tip/ff303e66c240ba6269e31817a386995440a18c99
Author: Peter Zijlstra <peterz@xxxxxxxxxxxxx>
AuthorDate: Fri, 17 Apr 2015 20:05:30 +0200
Committer: Ingo Molnar <mingo@xxxxxxxxxx>
CommitDate: Fri, 8 May 2015 12:25:38 +0200
perf: Fix software migrate events
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@xxxxxxxxxxxxx>
Cc: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
Cc: Borislav Petkov <bp@xxxxxxxxx>
Cc: H. Peter Anvin <hpa@xxxxxxxxx>
Cc: Linus Torvalds <torvalds@xxxxxxxxxxxxxxxxxxxx>
Cc: Peter Zijlstra <peterz@xxxxxxxxxxxxx>
Cc: Stephane Eranian <eranian@xxxxxxxxxx>
Cc: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
Signed-off-by: Ingo Molnar <mingo@xxxxxxxxxx>
---
include/linux/perf_event.h | 24 ++++++++++++++++++++++++
include/linux/sched.h | 7 ++++---
kernel/sched/core.c | 2 +-
3 files changed, 29 insertions(+), 4 deletions(-)
diff --git a/include/linux/perf_event.h b/include/linux/perf_event.h
index 61992cf..e86f85a 100644
--- a/include/linux/perf_event.h
+++ b/include/linux/perf_event.h
@@ -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
diff --git a/include/linux/sched.h b/include/linux/sched.h
index 26a2e61..2c5e6c3 100644
--- a/include/linux/sched.h
+++ b/include/linux/sched.h
@@ -1356,9 +1356,6 @@ struct task_struct {
#endif
struct mm_struct *mm, *active_mm;
-#ifdef CONFIG_COMPAT_BRK
- unsigned brk_randomized:1;
-#endif
/* per-thread vma caching */
u32 vmacache_seqnum;
struct vm_area_struct *vmacache[VMACACHE_SIZE];
@@ -1381,10 +1378,14 @@ struct task_struct {
/* Revert to default priority/policy when forking */
unsigned sched_reset_on_fork:1;
unsigned sched_contributes_to_load:1;
+ unsigned sched_migrated:1;
#ifdef CONFIG_MEMCG_KMEM
unsigned memcg_kmem_skip_account:1;
#endif
+#ifdef CONFIG_COMPAT_BRK
+ unsigned brk_randomized:1;
+#endif
unsigned long atomic_flags; /* Flags needing atomic access. */
diff --git a/kernel/sched/core.c b/kernel/sched/core.c
index fe22f75..8652fd5 100644
--- a/kernel/sched/core.c
+++ b/kernel/sched/core.c
@@ -1049,7 +1049,7 @@ void set_task_cpu(struct task_struct *p, unsigned int new_cpu)
if (p->sched_class->migrate_task_rq)
p->sched_class->migrate_task_rq(p, new_cpu);
p->se.nr_migrations++;
- perf_sw_event_sched(PERF_COUNT_SW_CPU_MIGRATIONS, 1, 0);
+ perf_event_task_migrate(p);
}
__set_task_cpu(p, new_cpu);
--
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