4 files changed, 78 insertions, 42 deletions

diff --git a/arch/x86/kernel/dumpstack_64.c b/arch/x86/kernel/dumpstack_64.c
index 6d728d9284bd..af7785ff5aa0 100644
--- a/arch/x86/kernel/dumpstack_64.c
+++ b/arch/x86/kernel/dumpstack_64.c
@@ -129,7 +129,7 @@ void dump_trace(struct task_struct *task, struct pt_regs *regs,
         if (!stack) {
                 if (regs)
                         stack = (unsigned long *)regs->sp;
-                else if (task && task != current)
+                else if (task != current)
                         stack = (unsigned long *)task->thread.sp;
                 else
                         stack = &dummy;
diff --git a/include/linux/perf_event.h b/include/linux/perf_event.h
index 0b91db2522cc..412b790f5da6 100644
--- a/include/linux/perf_event.h
+++ b/include/linux/perf_event.h
@@ -589,6 +589,7 @@ struct hw_perf_event {
         u64                             sample_period;
         u64                             last_period;
         local64_t                       period_left;
+        u64                             interrupts_seq;
         u64                             interrupts;
 
         u64                             freq_time_stamp;
diff --git a/kernel/events/core.c b/kernel/events/core.c
index de859fb4038f..7c3b9de55f6b 100644
--- a/kernel/events/core.c
+++ b/kernel/events/core.c
@@ -2300,6 +2300,9 @@ do {					\
         return div64_u64(dividend, divisor);
 }
 
+static DEFINE_PER_CPU(int, perf_throttled_count);
+static DEFINE_PER_CPU(u64, perf_throttled_seq);
+
 static void perf_adjust_period(struct perf_event *event, u64 nsec, u64 count)
 {
         struct hw_perf_event *hwc = &event->hw;
@@ -2325,16 +2328,29 @@ static void perf_adjust_period(struct perf_event *event, u64 nsec, u64 count)
         }
 }
 
-static void perf_ctx_adjust_freq(struct perf_event_context *ctx, u64 period)
+/*
+ * combine freq adjustment with unthrottling to avoid two passes over the
+ * events. At the same time, make sure, having freq events does not change
+ * the rate of unthrottling as that would introduce bias.
+ */
+static void perf_adjust_freq_unthr_context(struct perf_event_context *ctx,
+                                           int needs_unthr)
 {
         struct perf_event *event;
         struct hw_perf_event *hwc;
-        u64 interrupts, now;
+        u64 now, period = TICK_NSEC;
         s64 delta;
 
-        if (!ctx->nr_freq)
+        /*
+         * only need to iterate over all events iff:
+         * - context have events in frequency mode (needs freq adjust)
+         * - there are events to unthrottle on this cpu
+         */
+        if (!(ctx->nr_freq || needs_unthr))
                 return;
 
+        raw_spin_lock(&ctx->lock);
+
         list_for_each_entry_rcu(event, &ctx->event_list, event_entry) {
                 if (event->state != PERF_EVENT_STATE_ACTIVE)
                         continue;
@@ -2344,13 +2360,8 @@ static void perf_ctx_adjust_freq(struct perf_event_context *ctx, u64 period)
 
                 hwc = &event->hw;
 
-                interrupts = hwc->interrupts;
-                hwc->interrupts = 0;
-
-                /*
-                 * unthrottle events on the tick
-                 */
-                if (interrupts == MAX_INTERRUPTS) {
+                if (needs_unthr && hwc->interrupts == MAX_INTERRUPTS) {
+                        hwc->interrupts = 0;
                         perf_log_throttle(event, 1);
                         event->pmu->start(event, 0);
                 }
@@ -2358,14 +2369,26 @@ static void perf_ctx_adjust_freq(struct perf_event_context *ctx, u64 period)
                 if (!event->attr.freq || !event->attr.sample_freq)
                         continue;
 
-                event->pmu->read(event);
+                /*
+                 * stop the event and update event->count
+                 */
+                event->pmu->stop(event, PERF_EF_UPDATE);
+
                 now = local64_read(&event->count);
                 delta = now - hwc->freq_count_stamp;
                 hwc->freq_count_stamp = now;
 
+                /*
+                 * restart the event
+                 * reload only if value has changed
+                 */
                 if (delta > 0)
                         perf_adjust_period(event, period, delta);
+
+                event->pmu->start(event, delta > 0 ? PERF_EF_RELOAD : 0);
         }
+
+        raw_spin_unlock(&ctx->lock);
 }
 
 /*
@@ -2388,16 +2411,13 @@ static void rotate_ctx(struct perf_event_context *ctx)
  */
 static void perf_rotate_context(struct perf_cpu_context *cpuctx)
 {
-        u64 interval = (u64)cpuctx->jiffies_interval * TICK_NSEC;
         struct perf_event_context *ctx = NULL;
-        int rotate = 0, remove = 1, freq = 0;
+        int rotate = 0, remove = 1;
 
         if (cpuctx->ctx.nr_events) {
                 remove = 0;
                 if (cpuctx->ctx.nr_events != cpuctx->ctx.nr_active)
                         rotate = 1;
-                if (cpuctx->ctx.nr_freq)
-                        freq = 1;
         }
 
         ctx = cpuctx->task_ctx;
@@ -2405,37 +2425,26 @@ static void perf_rotate_context(struct perf_cpu_context *cpuctx)
                 remove = 0;
                 if (ctx->nr_events != ctx->nr_active)
                         rotate = 1;
-                if (ctx->nr_freq)
-                        freq = 1;
         }
 
-        if (!rotate && !freq)
+        if (!rotate)
                 goto done;
 
         perf_ctx_lock(cpuctx, cpuctx->task_ctx);
         perf_pmu_disable(cpuctx->ctx.pmu);
 
-        if (freq) {
-                perf_ctx_adjust_freq(&cpuctx->ctx, interval);
-                if (ctx)
-                        perf_ctx_adjust_freq(ctx, interval);
-        }
-
-        if (rotate) {
-                cpu_ctx_sched_out(cpuctx, EVENT_FLEXIBLE);
-                if (ctx)
-                        ctx_sched_out(ctx, cpuctx, EVENT_FLEXIBLE);
+        cpu_ctx_sched_out(cpuctx, EVENT_FLEXIBLE);
+        if (ctx)
+                ctx_sched_out(ctx, cpuctx, EVENT_FLEXIBLE);
 
-                rotate_ctx(&cpuctx->ctx);
-                if (ctx)
-                        rotate_ctx(ctx);
+        rotate_ctx(&cpuctx->ctx);
+        if (ctx)
+                rotate_ctx(ctx);
 
-                perf_event_sched_in(cpuctx, ctx, current);
-        }
+        perf_event_sched_in(cpuctx, ctx, current);
 
         perf_pmu_enable(cpuctx->ctx.pmu);
         perf_ctx_unlock(cpuctx, cpuctx->task_ctx);
-
 done:
         if (remove)
                 list_del_init(&cpuctx->rotation_list);
@@ -2445,10 +2454,22 @@ void perf_event_task_tick(void)
 {
         struct list_head *head = &__get_cpu_var(rotation_list);
         struct perf_cpu_context *cpuctx, *tmp;
+        struct perf_event_context *ctx;
+        int throttled;
 
         WARN_ON(!irqs_disabled());
 
+        __this_cpu_inc(perf_throttled_seq);
+        throttled = __this_cpu_xchg(perf_throttled_count, 0);
+
         list_for_each_entry_safe(cpuctx, tmp, head, rotation_list) {
+                ctx = &cpuctx->ctx;
+                perf_adjust_freq_unthr_context(ctx, throttled);
+
+                ctx = cpuctx->task_ctx;
+                if (ctx)
+                        perf_adjust_freq_unthr_context(ctx, throttled);
+
                 if (cpuctx->jiffies_interval == 1 ||
                                 !(jiffies % cpuctx->jiffies_interval))
                         perf_rotate_context(cpuctx);
@@ -4514,6 +4535,7 @@ static int __perf_event_overflow(struct perf_event *event,
 {
         int events = atomic_read(&event->event_limit);
         struct hw_perf_event *hwc = &event->hw;
+        u64 seq;
         int ret = 0;
 
         /*
@@ -4523,14 +4545,20 @@ static int __perf_event_overflow(struct perf_event *event,
         if (unlikely(!is_sampling_event(event)))
                 return 0;
 
-        if (unlikely(hwc->interrupts >= max_samples_per_tick)) {
-                if (throttle) {
+        seq = __this_cpu_read(perf_throttled_seq);
+        if (seq != hwc->interrupts_seq) {
+                hwc->interrupts_seq = seq;
+                hwc->interrupts = 1;
+        } else {
+                hwc->interrupts++;
+                if (unlikely(throttle
+                             && hwc->interrupts >= max_samples_per_tick)) {
+                        __this_cpu_inc(perf_throttled_count);
                         hwc->interrupts = MAX_INTERRUPTS;
                         perf_log_throttle(event, 0);
                         ret = 1;
                 }
-        } else
-                hwc->interrupts++;
+        }
 
         if (event->attr.freq) {
                 u64 now = perf_clock();
diff --git a/tools/perf/builtin-top.c b/tools/perf/builtin-top.c
index e8b033c074f9..d869b214ada2 100644
--- a/tools/perf/builtin-top.c
+++ b/tools/perf/builtin-top.c
@@ -88,8 +88,6 @@ void get_term_dimensions(struct winsize *ws)
 
 static void perf_top__update_print_entries(struct perf_top *top)
 {
-        top->print_entries = top->winsize.ws_row;
-
         if (top->print_entries > 9)
                 top->print_entries -= 9;
 }
@@ -99,6 +97,13 @@ static void perf_top__sig_winch(int sig __used, siginfo_t *info __used, void *ar
         struct perf_top *top = arg;
 
         get_term_dimensions(&top->winsize);
+        if (!top->print_entries
+            || (top->print_entries+4) > top->winsize.ws_row) {
+                top->print_entries = top->winsize.ws_row;
+        } else {
+                top->print_entries += 4;
+                top->winsize.ws_row = top->print_entries;
+        }
         perf_top__update_print_entries(top);
 }
 
@@ -452,8 +457,10 @@ static void perf_top__handle_keypress(struct perf_top *top, int c)
                                 };
                                 perf_top__sig_winch(SIGWINCH, NULL, top);
                                 sigaction(SIGWINCH, &act, NULL);
-                        } else
+                        } else {
+                                perf_top__sig_winch(SIGWINCH, NULL, top);
                                 signal(SIGWINCH, SIG_DFL);
+                        }
                         break;
                 case 'E':
                         if (top->evlist->nr_entries > 1) {