From ff303e66c240ba6269e31817a386995440a18c99 Mon Sep 17 00:00:00 2001 From: Peter Zijlstra Date: Fri, 17 Apr 2015 20:05:30 +0200 Subject: [PATCH] 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) Cc: Andrew Morton Cc: Borislav Petkov Cc: H. Peter Anvin Cc: Linus Torvalds Cc: Peter Zijlstra Cc: Stephane Eranian Cc: Thomas Gleixner Signed-off-by: Ingo Molnar --- 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 61992cf2e977..e86f85abeda7 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 26a2e6122734..2c5e6c3db654 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 fe22f7510bce..8652fd540780 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); -- 2.34.1