perf_counter: theres more to overflow than writing events

Prepare for more generic overflow handling. The new perf_counter_overflow()
method will handle the generic bits of the counter overflow, and can return
a !0 return value, in which case the counter should be (soft) disabled, so
that it won't count until it's properly disabled.

XXX: do powerpc and swcounter

Signed-off-by: Peter Zijlstra <a.p.zijlstra@chello.nl>
Cc: Paul Mackerras <paulus@samba.org>
Cc: Corey Ashford <cjashfor@linux.vnet.ibm.com>
LKML-Reference: <20090406094517.812109629@chello.nl>
Signed-off-by: Ingo Molnar <mingo@elte.hu>

arch/powerpc/kernel/perf_counter.c

@@ -732,7 +732,7 @@ static void record_and_restart(struct perf_counter *counter, long val,
 	 * Finally record data if requested.
 	 */
 	if (record)
-		perf_counter_output(counter, 1, regs);
+		perf_counter_overflow(counter, 1, regs);
 }
 
 /*

arch/x86/kernel/cpu/perf_counter.c

@@ -800,7 +800,8 @@ static int __smp_perf_counter_interrupt(struct pt_regs *regs, int nmi)
 			continue;
 
 		perf_save_and_restart(counter);
-		perf_counter_output(counter, nmi, regs);
+		if (perf_counter_overflow(counter, nmi, regs))
+			__pmc_generic_disable(counter, &counter->hw, bit);
 	}
 
 	hw_perf_ack_status(ack);

include/linux/perf_counter.h

@@ -491,8 +491,8 @@ extern int hw_perf_group_sched_in(struct perf_counter *group_leader,
 	       struct perf_counter_context *ctx, int cpu);
 extern void perf_counter_update_userpage(struct perf_counter *counter);
 
-extern void perf_counter_output(struct perf_counter *counter,
-				int nmi, struct pt_regs *regs);
+extern int perf_counter_overflow(struct perf_counter *counter,
+				 int nmi, struct pt_regs *regs);
 /*
  * Return 1 for a software counter, 0 for a hardware counter
  */

kernel/perf_counter.c

@@ -1800,8 +1800,8 @@ static void perf_output_end(struct perf_output_handle *handle)
 	rcu_read_unlock();
 }
 
-void perf_counter_output(struct perf_counter *counter,
-			 int nmi, struct pt_regs *regs)
+static void perf_counter_output(struct perf_counter *counter,
+				int nmi, struct pt_regs *regs)
 {
 	int ret;
 	u64 record_type = counter->hw_event.record_type;
@@ -2033,6 +2033,17 @@ void perf_counter_munmap(unsigned long addr, unsigned long len,
 	perf_counter_mmap_event(&mmap_event);
 }
 
+/*
+ * Generic counter overflow handling.
+ */
+
+int perf_counter_overflow(struct perf_counter *counter,
+			  int nmi, struct pt_regs *regs)
+{
+	perf_counter_output(counter, nmi, regs);
+	return 0;
+}
+
 /*
  * Generic software counter infrastructure
  */
@@ -2077,6 +2088,7 @@ static void perf_swcounter_set_period(struct perf_counter *counter)
 
 static enum hrtimer_restart perf_swcounter_hrtimer(struct hrtimer *hrtimer)
 {
+	enum hrtimer_restart ret = HRTIMER_RESTART;
 	struct perf_counter *counter;
 	struct pt_regs *regs;
 
@@ -2092,20 +2104,25 @@ static enum hrtimer_restart perf_swcounter_hrtimer(struct hrtimer *hrtimer)
 			!counter->hw_event.exclude_user)
 		regs = task_pt_regs(current);
 
-	if (regs)
-		perf_counter_output(counter, 0, regs);
+	if (regs) {
+		if (perf_counter_overflow(counter, 0, regs))
+			ret = HRTIMER_NORESTART;
+	}
 
 	hrtimer_forward_now(hrtimer, ns_to_ktime(counter->hw.irq_period));
 
-	return HRTIMER_RESTART;
+	return ret;
 }
 
 static void perf_swcounter_overflow(struct perf_counter *counter,
 				    int nmi, struct pt_regs *regs)
 {
 	perf_swcounter_update(counter);
 	perf_swcounter_set_period(counter);
-	perf_counter_output(counter, nmi, regs);
+	if (perf_counter_overflow(counter, nmi, regs))
+		/* soft-disable the counter */
+		;
+
 }
 
 static int perf_swcounter_match(struct perf_counter *counter,