linux-kernel - [PATCH] perf_counter: Always schedule all software counters in

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Date:	Mon, 12 Jan 2009 16:38:26 +1100
From:	Paul Mackerras <paulus@...ba.org>
To:	linux-kernel@...r.kernel.org
CC:	Ingo Molnar <mingo@...e.hu>, Thomas Gleixner <tglx@...utronix.de>
Subject: [PATCH] perf_counter: Always schedule all software counters in

Software counters aren't subject to the limitations imposed by the
fixed number of hardware counter registers, so there is no reason not
to enable them all in __perf_counter_sched_in.  Previously we used to
break out of the loop when we got to a group that wouldn't fit on the
PMU; with this we continue through the list but only schedule in
software counters (or groups containing only software counters) from
there on.

Signed-off-by: Paul Mackerras <paulus@...ba.org>
---
This is also available in my perfcounters git tree (master branch) at
git://git.kernel.org/pub/scm/linux/kernel/git/paulus/perfcounters.git

diff --git a/kernel/perf_counter.c b/kernel/perf_counter.c
index 4c0dccb..3aef306 100644
--- a/kernel/perf_counter.c
+++ b/kernel/perf_counter.c
@@ -455,12 +455,37 @@ group_error:
 	return -EAGAIN;
 }
 
+/*
+ * Return 1 for a software counter, 0 for a hardware counter
+ */
+static inline int is_software_counter(struct perf_counter *counter)
+{
+	return !counter->hw_event.raw && counter->hw_event.type < 0;
+}
+
+/*
+ * Return 1 for a group consisting entirely of software counters,
+ * 0 if the group contains any hardware counters.
+ */
+static int is_software_only_group(struct perf_counter *leader)
+{
+	struct perf_counter *counter;
+
+	if (!is_software_counter(leader))
+		return 0;
+	list_for_each_entry(counter, &leader->sibling_list, list_entry)
+		if (!is_software_counter(counter))
+			return 0;
+	return 1;
+}
+
 static void
 __perf_counter_sched_in(struct perf_counter_context *ctx,
 			struct perf_cpu_context *cpuctx, int cpu)
 {
 	struct perf_counter *counter;
 	u64 flags;
+	int can_add_hw = 1;
 
 	if (likely(!ctx->nr_counters))
 		return;
@@ -477,10 +502,12 @@ __perf_counter_sched_in(struct perf_counter_context *ctx,
 
 		/*
 		 * If we scheduled in a group atomically and exclusively,
-		 * or if this group can't go on, break out:
+		 * or if this group can't go on, don't add any more
+		 * hardware counters.
 		 */
-		if (group_sched_in(counter, cpuctx, ctx, cpu))
-			break;
+		if (can_add_hw || is_software_only_group(counter))
+			if (group_sched_in(counter, cpuctx, ctx, cpu))
+				can_add_hw = 0;
 	}
 	hw_perf_restore(flags);
 	spin_unlock(&ctx->lock);
--
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