perf counters: add prctl interface to disable/enable counters

Add a way for self-monitoring tasks to disable/enable counters summarily,
via a prctl:

	PR_TASK_PERF_COUNTERS_DISABLE		31
	PR_TASK_PERF_COUNTERS_ENABLE		32

Signed-off-by: Ingo Molnar <mingo@elte.hu>

2 files changed, 86 insertions, 7 deletions

diff --git a/kernel/perf_counter.c b/kernel/perf_counter.c
index a0fe8474ee29..4e679b91d8bb 100644
--- a/kernel/perf_counter.c
+++ b/kernel/perf_counter.c
@@ -415,6 +415,9 @@ counter_sched_in(struct perf_counter *counter,
                  struct perf_counter_context *ctx,
                  int cpu)
 {
+        if (counter->active == -1)
+                return;
+
         counter->hw_ops->hw_perf_counter_enable(counter);
         counter->active = 1;
         counter->oncpu = cpu;   /* TODO: put 'cpu' into cpuctx->cpu */
@@ -479,6 +482,79 @@ void perf_counter_task_sched_in(struct task_struct *task, int cpu)
         cpuctx->task_ctx = ctx;
 }
 
+int perf_counter_task_disable(void)
+{
+        struct task_struct *curr = current;
+        struct perf_counter_context *ctx = &curr->perf_counter_ctx;
+        struct perf_counter *counter;
+        u64 perf_flags;
+        int cpu;
+
+        if (likely(!ctx->nr_counters))
+                return 0;
+
+        local_irq_disable();
+        cpu = smp_processor_id();
+
+        perf_counter_task_sched_out(curr, cpu);
+
+        spin_lock(&ctx->lock);
+
+        /*
+         * Disable all the counters:
+         */
+        perf_flags = hw_perf_save_disable();
+
+        list_for_each_entry(counter, &ctx->counter_list, list_entry) {
+                WARN_ON_ONCE(counter->active == 1);
+                counter->active = -1;
+        }
+        hw_perf_restore(perf_flags);
+
+        spin_unlock(&ctx->lock);
+
+        local_irq_enable();
+
+        return 0;
+}
+
+int perf_counter_task_enable(void)
+{
+        struct task_struct *curr = current;
+        struct perf_counter_context *ctx = &curr->perf_counter_ctx;
+        struct perf_counter *counter;
+        u64 perf_flags;
+        int cpu;
+
+        if (likely(!ctx->nr_counters))
+                return 0;
+
+        local_irq_disable();
+        cpu = smp_processor_id();
+
+        spin_lock(&ctx->lock);
+
+        /*
+         * Disable all the counters:
+         */
+        perf_flags = hw_perf_save_disable();
+
+        list_for_each_entry(counter, &ctx->counter_list, list_entry) {
+                if (counter->active != -1)
+                        continue;
+                counter->active = 0;
+        }
+        hw_perf_restore(perf_flags);
+
+        spin_unlock(&ctx->lock);
+
+        perf_counter_task_sched_in(curr, cpu);
+
+        local_irq_enable();
+
+        return 0;
+}
+
 void perf_counter_task_tick(struct task_struct *curr, int cpu)
 {
         struct perf_counter_context *ctx = &curr->perf_counter_ctx;
@@ -951,13 +1027,9 @@ perf_counter_alloc(struct perf_counter_hw_event *hw_event,
  * @cpu:                target cpu
  * @group_fd:           group leader counter fd
  */
-asmlinkage int sys_perf_counter_open(
-
-        struct perf_counter_hw_event    *hw_event_uptr          __user,
-        pid_t                           pid,
-        int                             cpu,
-        int                             group_fd)
-
+asmlinkage int
+sys_perf_counter_open(struct perf_counter_hw_event *hw_event_uptr __user,
+                      pid_t pid, int cpu, int group_fd)
 {
         struct perf_counter *counter, *group_leader;
         struct perf_counter_hw_event hw_event;
diff --git a/kernel/sys.c b/kernel/sys.c
index 31deba8f7d16..0f66633be319 100644
--- a/kernel/sys.c
+++ b/kernel/sys.c
@@ -14,6 +14,7 @@
 #include <linux/prctl.h>
 #include <linux/highuid.h>
 #include <linux/fs.h>
+#include <linux/perf_counter.h>
 #include <linux/resource.h>
 #include <linux/kernel.h>
 #include <linux/kexec.h>
@@ -1716,6 +1717,12 @@ asmlinkage long sys_prctl(int option, unsigned long arg2, unsigned long arg3,
                 case PR_SET_TSC:
                         error = SET_TSC_CTL(arg2);
                         break;
+                case PR_TASK_PERF_COUNTERS_DISABLE:
+                        error = perf_counter_task_disable();
+                        break;
+                case PR_TASK_PERF_COUNTERS_ENABLE:
+                        error = perf_counter_task_enable();
+                        break;
                 case PR_GET_TIMERSLACK:
                         error = current->timer_slack_ns;
                         break;