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Date:	Tue, 31 Mar 2009 15:21:48 +0200
From:	Markus Metzger <markus.t.metzger@...el.com>
To:	linux-kernel@...r.kernel.org, mingo@...e.hu, tglx@...utronix.de,
	hpa@...or.com
Cc:	markus.t.metzger@...el.com, markus.t.metzger@...il.com,
	roland@...hat.com, eranian@...glemail.com, oleg@...hat.com,
	juan.villacis@...el.com, ak@...ux.jf.intel.com
Subject: [patch 9/21] x86, hw-branch-tracer: use new debug store interface

Make the hw-branch-tracer use the new debug store interface introduced in
patch 7.

Remove the unnecessary spinlock.


Signed-off-by: Markus Metzger <markus.t.metzger@...el.com>
---

Index: git-tip/kernel/trace/trace_hw_branches.c
===================================================================
--- git-tip.orig/kernel/trace/trace_hw_branches.c	2009-03-30 13:31:09.000000000 +0200
+++ git-tip/kernel/trace/trace_hw_branches.c	2009-03-30 19:00:53.000000000 +0200
@@ -4,7 +4,6 @@
  * Copyright (C) 2008-2009 Intel Corporation.
  * Markus Metzger <markus.t.metzger@...il.com>, 2008-2009
  */
-#include <linux/spinlock.h>
 #include <linux/kallsyms.h>
 #include <linux/debugfs.h>
 #include <linux/ftrace.h>
@@ -21,168 +20,108 @@
 
 #define BTS_BUFFER_SIZE (1 << 13)
 
-/*
- * The tracer lock protects the below per-cpu tracer array.
- * It needs to be held to:
- * - start tracing on all cpus
- * - stop tracing on all cpus
- * - start tracing on a single hotplug cpu
- * - stop tracing on a single hotplug cpu
- * - read the trace from all cpus
- * - read the trace from a single cpu
- */
-static DEFINE_SPINLOCK(bts_tracer_lock);
 static DEFINE_PER_CPU(struct bts_tracer *, tracer);
 static DEFINE_PER_CPU(unsigned char[BTS_BUFFER_SIZE], buffer);
 
 #define this_tracer per_cpu(tracer, smp_processor_id())
-#define this_buffer per_cpu(buffer, smp_processor_id())
 
 static int trace_hw_branches_enabled __read_mostly;
 static int trace_hw_branches_suspended __read_mostly;
 static struct trace_array *hw_branch_trace __read_mostly;
 
 
-/*
- * Initialize the tracer for the current cpu.
- * The argument is ignored.
- *
- * pre: bts_tracer_lock must be locked.
- */
-static void bts_trace_init_cpu(void *arg)
+static void bts_trace_init_cpu(int cpu)
 {
-	if (this_tracer)
-		ds_release_bts(this_tracer);
+	per_cpu(tracer, cpu) =
+		ds_request_bts_cpu(cpu, per_cpu(buffer, cpu), BTS_BUFFER_SIZE,
+				   NULL, (size_t)-1, BTS_KERNEL);
 
-	this_tracer = ds_request_bts(NULL, this_buffer, BTS_BUFFER_SIZE,
-				     NULL, (size_t)-1, BTS_KERNEL);
-	if (IS_ERR(this_tracer)) {
-		this_tracer = NULL;
-		return;
-	}
+	if (IS_ERR(per_cpu(tracer, cpu)))
+		per_cpu(tracer, cpu) = NULL;
 }
 
 static int bts_trace_init(struct trace_array *tr)
 {
-	int cpu, avail;
-
-	spin_lock(&bts_tracer_lock);
+	int cpu;
 
 	hw_branch_trace = tr;
+	trace_hw_branches_enabled = 0;
 
-	on_each_cpu(bts_trace_init_cpu, NULL, 1);
+	get_online_cpus();
+	for_each_online_cpu(cpu) {
+		bts_trace_init_cpu(cpu);
 
-	/* Check on how many cpus we could enable tracing */
-	avail = 0;
-	for_each_online_cpu(cpu)
 		if (per_cpu(tracer, cpu))
-			avail++;
-
-	trace_hw_branches_enabled = (avail ? 1 : 0);
+			trace_hw_branches_enabled = 1;
+	}
 	trace_hw_branches_suspended = 0;
-
-	spin_unlock(&bts_tracer_lock);
-
+	put_online_cpus();
 
 	/* If we could not enable tracing on a single cpu, we fail. */
-	return avail ? 0 : -EOPNOTSUPP;
-}
-
-/*
- * Release the tracer for the current cpu.
- * The argument is ignored.
- *
- * pre: bts_tracer_lock must be locked.
- */
-static void bts_trace_release_cpu(void *arg)
-{
-	if (this_tracer) {
-		ds_release_bts(this_tracer);
-		this_tracer = NULL;
-	}
+	return trace_hw_branches_enabled ? 0 : -EOPNOTSUPP;
 }
 
 static void bts_trace_reset(struct trace_array *tr)
 {
-	spin_lock(&bts_tracer_lock);
+	int cpu;
 
-	on_each_cpu(bts_trace_release_cpu, NULL, 1);
+	get_online_cpus();
+	for_each_online_cpu(cpu) {
+		ds_release_bts(per_cpu(tracer, cpu));
+		per_cpu(tracer, cpu) = NULL;
+	}
 	trace_hw_branches_enabled = 0;
 	trace_hw_branches_suspended = 0;
-
-	spin_unlock(&bts_tracer_lock);
-}
-
-/*
- * Resume tracing on the current cpu.
- * The argument is ignored.
- *
- * pre: bts_tracer_lock must be locked.
- */
-static void bts_trace_resume_cpu(void *arg)
-{
-	if (this_tracer)
-		ds_resume_bts(this_tracer);
+	put_online_cpus();
 }
 
 static void bts_trace_start(struct trace_array *tr)
 {
-	spin_lock(&bts_tracer_lock);
+	int cpu;
 
-	on_each_cpu(bts_trace_resume_cpu, NULL, 1);
+	get_online_cpus();
+	for_each_online_cpu(cpu)
+		if (per_cpu(tracer, cpu))
+			ds_resume_bts(per_cpu(tracer, cpu));
 	trace_hw_branches_suspended = 0;
-
-	spin_unlock(&bts_tracer_lock);
-}
-
-/*
- * Suspend tracing on the current cpu.
- * The argument is ignored.
- *
- * pre: bts_tracer_lock must be locked.
- */
-static void bts_trace_suspend_cpu(void *arg)
-{
-	if (this_tracer)
-		ds_suspend_bts(this_tracer);
+	put_online_cpus();
 }
 
 static void bts_trace_stop(struct trace_array *tr)
 {
-	spin_lock(&bts_tracer_lock);
+	int cpu;
 
-	on_each_cpu(bts_trace_suspend_cpu, NULL, 1);
+	get_online_cpus();
+	for_each_online_cpu(cpu)
+		if (per_cpu(tracer, cpu))
+			ds_suspend_bts(per_cpu(tracer, cpu));
 	trace_hw_branches_suspended = 1;
-
-	spin_unlock(&bts_tracer_lock);
+	put_online_cpus();
 }
 
 static int __cpuinit bts_hotcpu_handler(struct notifier_block *nfb,
 				     unsigned long action, void *hcpu)
 {
-	unsigned int cpu = (unsigned long)hcpu;
-
-	spin_lock(&bts_tracer_lock);
-
-	if (!trace_hw_branches_enabled)
-		goto out;
+	int cpu = (long)hcpu;
 
 	switch (action) {
 	case CPU_ONLINE:
 	case CPU_DOWN_FAILED:
-		smp_call_function_single(cpu, bts_trace_init_cpu, NULL, 1);
-
-		if (trace_hw_branches_suspended)
-			smp_call_function_single(cpu, bts_trace_suspend_cpu,
-						 NULL, 1);
+		/* The notification is sent with interrupts enabled. */
+		if (trace_hw_branches_enabled) {
+			bts_trace_init_cpu(cpu);
+
+			if (trace_hw_branches_suspended)
+				ds_suspend_bts(per_cpu(tracer, cpu));
+		}
 		break;
+
 	case CPU_DOWN_PREPARE:
-		smp_call_function_single(cpu, bts_trace_release_cpu, NULL, 1);
-		break;
+		/* The notification is sent with interrupts enabled. */
+		ds_release_bts(per_cpu(tracer, cpu));
+		per_cpu(tracer, cpu) = NULL;
 	}
 
- out:
-	spin_unlock(&bts_tracer_lock);
 	return NOTIFY_DONE;
 }
 
@@ -274,7 +213,7 @@ static void trace_bts_at(const struct bt
 /*
  * Collect the trace on the current cpu and write it into the ftrace buffer.
  *
- * pre: bts_tracer_lock must be locked
+ * pre: tracing must be suspended on the current cpu
  */
 static void trace_bts_cpu(void *arg)
 {
@@ -291,10 +230,9 @@ static void trace_bts_cpu(void *arg)
 	if (unlikely(!this_tracer))
 		return;
 
-	ds_suspend_bts(this_tracer);
 	trace = ds_read_bts(this_tracer);
 	if (!trace)
-		goto out;
+		return;
 
 	for (at = trace->ds.top; (void *)at < trace->ds.end;
 	     at += trace->ds.size)
@@ -303,18 +241,25 @@ static void trace_bts_cpu(void *arg)
 	for (at = trace->ds.begin; (void *)at < trace->ds.top;
 	     at += trace->ds.size)
 		trace_bts_at(trace, at);
-
-out:
-	ds_resume_bts(this_tracer);
 }
 
 static void trace_bts_prepare(struct trace_iterator *iter)
 {
-	spin_lock(&bts_tracer_lock);
+	int cpu;
 
+	get_online_cpus();
+	for_each_online_cpu(cpu)
+		ds_suspend_bts(per_cpu(tracer, cpu));
+	/*
+	 * We need to collect the trace on the respective cpu since ftrace
+	 * implicitly adds the record for the current cpu.
+	 * Once that is more flexible, we could collect the data from any cpu.
+	 */
 	on_each_cpu(trace_bts_cpu, iter->tr, 1);
 
-	spin_unlock(&bts_tracer_lock);
+	for_each_online_cpu(cpu)
+		ds_resume_bts(per_cpu(tracer, cpu));
+	put_online_cpus();
 }
 
 static void trace_bts_close(struct trace_iterator *iter)
@@ -324,12 +269,11 @@ static void trace_bts_close(struct trace
 
 void trace_hw_branch_oops(void)
 {
-	spin_lock(&bts_tracer_lock);
-
-	if (trace_hw_branches_enabled)
+	if (this_tracer) {
+		ds_suspend_bts_noirq(this_tracer);
 		trace_bts_cpu(hw_branch_trace);
-
-	spin_unlock(&bts_tracer_lock);
+		ds_resume_bts_noirq(this_tracer);
+	}
 }
 
 struct tracer bts_tracer __read_mostly =
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