perf_counter: unify and fix delayed counter wakeup
While going over the wakeup code I noticed delayed wakeups only work
for hardware counters but basically all software counters rely on
them.
This patch unifies and generalizes the delayed wakeup to fix this
issue.
Since we're dealing with NMI context bits here, use a cmpxchg() based
single link list implementation to track counters that have pending
wakeups.
[ This should really be generic code for delayed wakeups, but since we
cannot use cmpxchg()/xchg() in generic code, I've let it live in the
perf_counter code. -- Eric Dumazet could use it to aggregate the
network wakeups. ]
Furthermore, the x86 method of using TIF flags was flawed in that its
quite possible to end up setting the bit on the idle task, loosing the
wakeup.
The powerpc method uses per-cpu storage and does appear to be
sufficient.
Signed-off-by: Peter Zijlstra <a.p.zijlstra@chello.nl>
Acked-by: Paul Mackerras <paulus@samba.org>
Orig-LKML-Reference: <20090330171023.153932974@chello.nl>
Signed-off-by: Ingo Molnar <mingo@elte.hu>
diff --git a/arch/powerpc/include/asm/hw_irq.h b/arch/powerpc/include/asm/hw_irq.h
index cb32d57..20a44d0 100644
--- a/arch/powerpc/include/asm/hw_irq.h
+++ b/arch/powerpc/include/asm/hw_irq.h
@@ -132,7 +132,7 @@
struct irq_chip;
#ifdef CONFIG_PERF_COUNTERS
-static inline unsigned long get_perf_counter_pending(void)
+static inline unsigned long test_perf_counter_pending(void)
{
unsigned long x;
@@ -160,7 +160,7 @@
#else
-static inline unsigned long get_perf_counter_pending(void)
+static inline unsigned long test_perf_counter_pending(void)
{
return 0;
}
diff --git a/arch/powerpc/kernel/irq.c b/arch/powerpc/kernel/irq.c
index 469e963..2cd471f 100644
--- a/arch/powerpc/kernel/irq.c
+++ b/arch/powerpc/kernel/irq.c
@@ -135,7 +135,7 @@
iseries_handle_interrupts();
}
- if (get_perf_counter_pending()) {
+ if (test_perf_counter_pending()) {
clear_perf_counter_pending();
perf_counter_do_pending();
}
diff --git a/arch/powerpc/kernel/perf_counter.c b/arch/powerpc/kernel/perf_counter.c
index df007fe..cde720f 100644
--- a/arch/powerpc/kernel/perf_counter.c
+++ b/arch/powerpc/kernel/perf_counter.c
@@ -650,24 +650,6 @@
}
/*
- * Handle wakeups.
- */
-void perf_counter_do_pending(void)
-{
- int i;
- struct cpu_hw_counters *cpuhw = &__get_cpu_var(cpu_hw_counters);
- struct perf_counter *counter;
-
- for (i = 0; i < cpuhw->n_counters; ++i) {
- counter = cpuhw->counter[i];
- if (counter && counter->wakeup_pending) {
- counter->wakeup_pending = 0;
- wake_up(&counter->waitq);
- }
- }
-}
-
-/*
* A counter has overflowed; update its count and record
* things if requested. Note that interrupts are hard-disabled
* here so there is no possibility of being interrupted.
@@ -720,7 +702,7 @@
struct cpu_hw_counters *cpuhw = &__get_cpu_var(cpu_hw_counters);
struct perf_counter *counter;
long val;
- int need_wakeup = 0, found = 0;
+ int found = 0;
for (i = 0; i < cpuhw->n_counters; ++i) {
counter = cpuhw->counter[i];
@@ -761,7 +743,7 @@
* immediately; otherwise we'll have do the wakeup when interrupts
* get soft-enabled.
*/
- if (get_perf_counter_pending() && regs->softe) {
+ if (test_perf_counter_pending() && regs->softe) {
irq_enter();
clear_perf_counter_pending();
perf_counter_do_pending();
diff --git a/arch/x86/include/asm/perf_counter.h b/arch/x86/include/asm/perf_counter.h
index 1662043..e2b0e66 100644
--- a/arch/x86/include/asm/perf_counter.h
+++ b/arch/x86/include/asm/perf_counter.h
@@ -84,8 +84,9 @@
#define MSR_ARCH_PERFMON_FIXED_CTR2 0x30b
#define X86_PMC_IDX_FIXED_BUS_CYCLES (X86_PMC_IDX_FIXED + 2)
-#define set_perf_counter_pending() \
- set_tsk_thread_flag(current, TIF_PERF_COUNTERS);
+#define set_perf_counter_pending() do { } while (0)
+#define clear_perf_counter_pending() do { } while (0)
+#define test_perf_counter_pending() (0)
#ifdef CONFIG_PERF_COUNTERS
extern void init_hw_perf_counters(void);
diff --git a/arch/x86/include/asm/thread_info.h b/arch/x86/include/asm/thread_info.h
index 3ffd5d2..8820a73 100644
--- a/arch/x86/include/asm/thread_info.h
+++ b/arch/x86/include/asm/thread_info.h
@@ -83,7 +83,6 @@
#define TIF_SYSCALL_AUDIT 7 /* syscall auditing active */
#define TIF_SECCOMP 8 /* secure computing */
#define TIF_MCE_NOTIFY 10 /* notify userspace of an MCE */
-#define TIF_PERF_COUNTERS 11 /* notify perf counter work */
#define TIF_NOTSC 16 /* TSC is not accessible in userland */
#define TIF_IA32 17 /* 32bit process */
#define TIF_FORK 18 /* ret_from_fork */
@@ -107,7 +106,6 @@
#define _TIF_SYSCALL_AUDIT (1 << TIF_SYSCALL_AUDIT)
#define _TIF_SECCOMP (1 << TIF_SECCOMP)
#define _TIF_MCE_NOTIFY (1 << TIF_MCE_NOTIFY)
-#define _TIF_PERF_COUNTERS (1 << TIF_PERF_COUNTERS)
#define _TIF_NOTSC (1 << TIF_NOTSC)
#define _TIF_IA32 (1 << TIF_IA32)
#define _TIF_FORK (1 << TIF_FORK)
@@ -141,7 +139,7 @@
/* Only used for 64 bit */
#define _TIF_DO_NOTIFY_MASK \
- (_TIF_SIGPENDING|_TIF_MCE_NOTIFY|_TIF_PERF_COUNTERS|_TIF_NOTIFY_RESUME)
+ (_TIF_SIGPENDING|_TIF_MCE_NOTIFY|_TIF_NOTIFY_RESUME)
/* flags to check in __switch_to() */
#define _TIF_WORK_CTXSW \
diff --git a/arch/x86/kernel/cpu/perf_counter.c b/arch/x86/kernel/cpu/perf_counter.c
index 3f95b0c..7aab177 100644
--- a/arch/x86/kernel/cpu/perf_counter.c
+++ b/arch/x86/kernel/cpu/perf_counter.c
@@ -227,7 +227,6 @@
*/
hwc->config |= pmc_ops->event_map(perf_event_id(hw_event));
}
- counter->wakeup_pending = 0;
return 0;
}
@@ -773,34 +772,6 @@
irq_exit();
}
-/*
- * This handler is triggered by NMI contexts:
- */
-void perf_counter_notify(struct pt_regs *regs)
-{
- struct cpu_hw_counters *cpuc;
- unsigned long flags;
- int bit, cpu;
-
- local_irq_save(flags);
- cpu = smp_processor_id();
- cpuc = &per_cpu(cpu_hw_counters, cpu);
-
- for_each_bit(bit, cpuc->used, X86_PMC_IDX_MAX) {
- struct perf_counter *counter = cpuc->counters[bit];
-
- if (!counter)
- continue;
-
- if (counter->wakeup_pending) {
- counter->wakeup_pending = 0;
- wake_up(&counter->waitq);
- }
- }
-
- local_irq_restore(flags);
-}
-
void perf_counters_lapic_init(int nmi)
{
u32 apic_val;
diff --git a/arch/x86/kernel/signal.c b/arch/x86/kernel/signal.c
index 611615a..0a813b1 100644
--- a/arch/x86/kernel/signal.c
+++ b/arch/x86/kernel/signal.c
@@ -6,7 +6,6 @@
* 2000-06-20 Pentium III FXSR, SSE support by Gareth Hughes
* 2000-2002 x86-64 support by Andi Kleen
*/
-#include <linux/perf_counter.h>
#include <linux/sched.h>
#include <linux/mm.h>
#include <linux/smp.h>
@@ -872,11 +871,6 @@
tracehook_notify_resume(regs);
}
- if (thread_info_flags & _TIF_PERF_COUNTERS) {
- clear_thread_flag(TIF_PERF_COUNTERS);
- perf_counter_notify(regs);
- }
-
#ifdef CONFIG_X86_32
clear_thread_flag(TIF_IRET);
#endif /* CONFIG_X86_32 */
diff --git a/include/linux/perf_counter.h b/include/linux/perf_counter.h
index 6bf67ce..0d83322 100644
--- a/include/linux/perf_counter.h
+++ b/include/linux/perf_counter.h
@@ -275,6 +275,10 @@
void *data_pages[0];
};
+struct perf_wakeup_entry {
+ struct perf_wakeup_entry *next;
+};
+
/**
* struct perf_counter - performance counter kernel representation:
*/
@@ -350,7 +354,7 @@
/* poll related */
wait_queue_head_t waitq;
/* optional: for NMIs */
- int wakeup_pending;
+ struct perf_wakeup_entry wakeup;
void (*destroy)(struct perf_counter *);
struct rcu_head rcu_head;
@@ -427,7 +431,7 @@
extern void perf_counter_task_tick(struct task_struct *task, int cpu);
extern void perf_counter_init_task(struct task_struct *child);
extern void perf_counter_exit_task(struct task_struct *child);
-extern void perf_counter_notify(struct pt_regs *regs);
+extern void perf_counter_do_pending(void);
extern void perf_counter_print_debug(void);
extern void perf_counter_unthrottle(void);
extern u64 hw_perf_save_disable(void);
@@ -461,7 +465,7 @@
perf_counter_task_tick(struct task_struct *task, int cpu) { }
static inline void perf_counter_init_task(struct task_struct *child) { }
static inline void perf_counter_exit_task(struct task_struct *child) { }
-static inline void perf_counter_notify(struct pt_regs *regs) { }
+static inline void perf_counter_do_pending(void) { }
static inline void perf_counter_print_debug(void) { }
static inline void perf_counter_unthrottle(void) { }
static inline void hw_perf_restore(u64 ctrl) { }
@@ -469,8 +473,9 @@
static inline int perf_counter_task_disable(void) { return -EINVAL; }
static inline int perf_counter_task_enable(void) { return -EINVAL; }
-static inline void perf_swcounter_event(u32 event, u64 nr,
- int nmi, struct pt_regs *regs) { }
+static inline void
+perf_swcounter_event(u32 event, u64 nr, int nmi, struct pt_regs *regs) { }
+
#endif
#endif /* __KERNEL__ */
diff --git a/kernel/perf_counter.c b/kernel/perf_counter.c
index 3b862a7..f70ff80 100644
--- a/kernel/perf_counter.c
+++ b/kernel/perf_counter.c
@@ -1197,8 +1197,12 @@
kfree(counter);
}
+static void perf_pending_sync(struct perf_counter *counter);
+
static void free_counter(struct perf_counter *counter)
{
+ perf_pending_sync(counter);
+
if (counter->destroy)
counter->destroy(counter);
@@ -1529,6 +1533,118 @@
};
/*
+ * Perf counter wakeup
+ *
+ * If there's data, ensure we set the poll() state and publish everything
+ * to user-space before waking everybody up.
+ */
+
+void perf_counter_wakeup(struct perf_counter *counter)
+{
+ struct perf_mmap_data *data;
+
+ rcu_read_lock();
+ data = rcu_dereference(counter->data);
+ if (data) {
+ (void)atomic_xchg(&data->wakeup, POLL_IN);
+ __perf_counter_update_userpage(counter, data);
+ }
+ rcu_read_unlock();
+
+ wake_up_all(&counter->waitq);
+}
+
+/*
+ * Pending wakeups
+ *
+ * Handle the case where we need to wakeup up from NMI (or rq->lock) context.
+ *
+ * The NMI bit means we cannot possibly take locks. Therefore, maintain a
+ * single linked list and use cmpxchg() to add entries lockless.
+ */
+
+#define PENDING_TAIL ((struct perf_wakeup_entry *)-1UL)
+
+static DEFINE_PER_CPU(struct perf_wakeup_entry *, perf_wakeup_head) = {
+ PENDING_TAIL,
+};
+
+static void perf_pending_queue(struct perf_counter *counter)
+{
+ struct perf_wakeup_entry **head;
+ struct perf_wakeup_entry *prev, *next;
+
+ if (cmpxchg(&counter->wakeup.next, NULL, PENDING_TAIL) != NULL)
+ return;
+
+ head = &get_cpu_var(perf_wakeup_head);
+
+ do {
+ prev = counter->wakeup.next = *head;
+ next = &counter->wakeup;
+ } while (cmpxchg(head, prev, next) != prev);
+
+ set_perf_counter_pending();
+
+ put_cpu_var(perf_wakeup_head);
+}
+
+static int __perf_pending_run(void)
+{
+ struct perf_wakeup_entry *list;
+ int nr = 0;
+
+ list = xchg(&__get_cpu_var(perf_wakeup_head), PENDING_TAIL);
+ while (list != PENDING_TAIL) {
+ struct perf_counter *counter = container_of(list,
+ struct perf_counter, wakeup);
+
+ list = list->next;
+
+ counter->wakeup.next = NULL;
+ /*
+ * Ensure we observe the unqueue before we issue the wakeup,
+ * so that we won't be waiting forever.
+ * -- see perf_not_pending().
+ */
+ smp_wmb();
+
+ perf_counter_wakeup(counter);
+ nr++;
+ }
+
+ return nr;
+}
+
+static inline int perf_not_pending(struct perf_counter *counter)
+{
+ /*
+ * If we flush on whatever cpu we run, there is a chance we don't
+ * need to wait.
+ */
+ get_cpu();
+ __perf_pending_run();
+ put_cpu();
+
+ /*
+ * Ensure we see the proper queue state before going to sleep
+ * so that we do not miss the wakeup. -- see perf_pending_handle()
+ */
+ smp_rmb();
+ return counter->wakeup.next == NULL;
+}
+
+static void perf_pending_sync(struct perf_counter *counter)
+{
+ wait_event(counter->waitq, perf_not_pending(counter));
+}
+
+void perf_counter_do_pending(void)
+{
+ __perf_pending_run();
+}
+
+/*
* Output
*/
@@ -1611,13 +1727,10 @@
static void perf_output_end(struct perf_output_handle *handle, int nmi)
{
if (handle->wakeup) {
- (void)atomic_xchg(&handle->data->wakeup, POLL_IN);
- __perf_counter_update_userpage(handle->counter, handle->data);
- if (nmi) {
- handle->counter->wakeup_pending = 1;
- set_perf_counter_pending();
- } else
- wake_up(&handle->counter->waitq);
+ if (nmi)
+ perf_pending_queue(handle->counter);
+ else
+ perf_counter_wakeup(handle->counter);
}
rcu_read_unlock();
}
@@ -2211,7 +2324,6 @@
counter->cpu = cpu;
counter->hw_event = *hw_event;
- counter->wakeup_pending = 0;
counter->group_leader = group_leader;
counter->hw_ops = NULL;
counter->ctx = ctx;
diff --git a/kernel/timer.c b/kernel/timer.c
index b455556..672ca25 100644
--- a/kernel/timer.c
+++ b/kernel/timer.c
@@ -37,6 +37,7 @@
#include <linux/delay.h>
#include <linux/tick.h>
#include <linux/kallsyms.h>
+#include <linux/perf_counter.h>
#include <asm/uaccess.h>
#include <asm/unistd.h>
@@ -1167,6 +1168,8 @@
{
struct tvec_base *base = __get_cpu_var(tvec_bases);
+ perf_counter_do_pending();
+
hrtimer_run_pending();
if (time_after_eq(jiffies, base->timer_jiffies))