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Date: Fri, 16 Jan 2009 11:50:51 +0100
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,
srostedt@...hat.com, ak@...ux.jf.intel.com
Subject: [patch 1/5] x86, ftrace, hw-branch-tracer: support hotplug cpus
Support hotplug cpus.
Reported-by: Andi Kleen <ak@...ux.intel.com>
Signed-off-by: Markus Metzger <markus.t.metzger@...el.com>
---
Index: ftrace/kernel/trace/trace_hw_branches.c
===================================================================
--- ftrace.orig/kernel/trace/trace_hw_branches.c 2009-01-14 15:21:46.000000000 +0100
+++ ftrace/kernel/trace/trace_hw_branches.c 2009-01-14 15:25:42.000000000 +0100
@@ -1,7 +1,8 @@
/*
* h/w branch tracer for x86 based on bts
*
- * Copyright (C) 2008 Markus Metzger <markus.t.metzger@...il.com>
+ * Copyright (C) 2008-2009 Intel Corporation.
+ * Markus Metzger <markus.t.metzger@...il.com>, 2008-2009
*
*/
@@ -10,6 +11,9 @@
#include <linux/debugfs.h>
#include <linux/ftrace.h>
#include <linux/kallsyms.h>
+#include <linux/mutex.h>
+#include <linux/cpu.h>
+#include <linux/smp.h>
#include <asm/ds.h>
@@ -18,13 +22,31 @@
#define SIZEOF_BTS (1 << 13)
+/* The tracer mutex 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_MUTEX(bts_tracer_mutex);
static DEFINE_PER_CPU(struct bts_tracer *, tracer);
static DEFINE_PER_CPU(unsigned char[SIZEOF_BTS], buffer);
#define this_tracer per_cpu(tracer, smp_processor_id())
#define this_buffer per_cpu(buffer, smp_processor_id())
+static int __read_mostly trace_hw_branches_enabled;
+
+/*
+ * Start tracing on the current cpu.
+ * The argument is ignored.
+ *
+ * pre: bts_tracer_mutex must be locked.
+ */
static void bts_trace_start_cpu(void *arg)
{
if (this_tracer)
@@ -42,14 +64,20 @@
static void bts_trace_start(struct trace_array *tr)
{
- int cpu;
+ mutex_lock(&bts_tracer_mutex);
- tracing_reset_online_cpus(tr);
+ on_each_cpu(bts_trace_start_cpu, NULL, 1);
+ trace_hw_branches_enabled = 1;
- for_each_cpu_mask(cpu, cpu_possible_map)
- smp_call_function_single(cpu, bts_trace_start_cpu, NULL, 1);
+ mutex_unlock(&bts_tracer_mutex);
}
+/*
+ * Start tracing on the current cpu.
+ * The argument is ignored.
+ *
+ * pre: bts_tracer_mutex must be locked.
+ */
static void bts_trace_stop_cpu(void *arg)
{
if (this_tracer) {
@@ -60,20 +88,58 @@
static void bts_trace_stop(struct trace_array *tr)
{
- int cpu;
+ mutex_lock(&bts_tracer_mutex);
- for_each_cpu_mask(cpu, cpu_possible_map)
+ trace_hw_branches_enabled = 0;
+ on_each_cpu(bts_trace_stop_cpu, NULL, 1);
+
+ mutex_unlock(&bts_tracer_mutex);
+}
+
+static int __cpuinit bts_hotcpu_handler(struct notifier_block *nfb,
+ unsigned long action, void *hcpu)
+{
+ unsigned int cpu = (unsigned long)hcpu;
+
+ mutex_lock(&bts_tracer_mutex);
+
+ if (!trace_hw_branches_enabled)
+ goto out;
+
+ switch (action) {
+ case CPU_ONLINE:
+ case CPU_DOWN_FAILED:
+ smp_call_function_single(cpu, bts_trace_start_cpu, NULL, 1);
+ break;
+ case CPU_DOWN_PREPARE:
smp_call_function_single(cpu, bts_trace_stop_cpu, NULL, 1);
+ break;
+ }
+
+ out:
+ mutex_unlock(&bts_tracer_mutex);
+ return NOTIFY_DONE;
}
+static struct notifier_block bts_hotcpu_notifier __cpuinitdata = {
+ .notifier_call = bts_hotcpu_handler
+};
+
static int bts_trace_init(struct trace_array *tr)
{
+ register_hotcpu_notifier(&bts_hotcpu_notifier);
tracing_reset_online_cpus(tr);
bts_trace_start(tr);
return 0;
}
+static void bts_trace_reset(struct trace_array *tr)
+{
+ bts_trace_stop(tr);
+ unregister_hotcpu_notifier(&bts_hotcpu_notifier);
+}
+
static void bts_trace_print_header(struct seq_file *m)
{
seq_puts(m,
@@ -107,18 +173,34 @@
{
struct ring_buffer_event *event;
struct hw_branch_entry *entry;
- unsigned long irq;
+ unsigned long irq1, irq2;
+ int cpu;
+
+ if (unlikely(!tr))
+ return;
+
+ if (unlikely(!trace_hw_branches_enabled))
+ return;
+
+ local_irq_save(irq1);
+ cpu = raw_smp_processor_id();
+ if (atomic_inc_return(&tr->data[cpu]->disabled) != 1)
+ goto out;
- event = ring_buffer_lock_reserve(tr->buffer, sizeof(*entry), &irq);
+ event = ring_buffer_lock_reserve(tr->buffer, sizeof(*entry), &irq2);
if (!event)
return;
entry = ring_buffer_event_data(event);
tracing_generic_entry_update(&entry->ent, 0, from);
entry->ent.type = TRACE_HW_BRANCHES;
- entry->ent.cpu = smp_processor_id();
+ entry->ent.cpu = cpu;
entry->from = from;
entry->to = to;
- ring_buffer_unlock_commit(tr->buffer, event, irq);
+ ring_buffer_unlock_commit(tr->buffer, event, irq2);
+
+ out:
+ atomic_dec(&tr->data[cpu]->disabled);
+ local_irq_restore(irq1);
}
static void trace_bts_at(struct trace_array *tr,
@@ -142,6 +224,11 @@
}
}
+/*
+ * Collect the trace on the current cpu and write it into the ftrace buffer.
+ *
+ * pre: bts_tracer_mutex must be locked
+ */
static void trace_bts_cpu(void *arg)
{
struct trace_array *tr = (struct trace_array *) arg;
@@ -151,6 +238,9 @@
if (!this_tracer)
return;
+ if (unlikely(atomic_read(&tr->data[raw_smp_processor_id()]->disabled)))
+ return;
+
ds_suspend_bts(this_tracer);
trace = ds_read_bts(this_tracer);
if (!trace)
@@ -170,17 +260,18 @@
static void trace_bts_prepare(struct trace_iterator *iter)
{
- int cpu;
+ mutex_lock(&bts_tracer_mutex);
+
+ on_each_cpu(trace_bts_cpu, iter->tr, 1);
- for_each_cpu_mask(cpu, cpu_possible_map)
- smp_call_function_single(cpu, trace_bts_cpu, iter->tr, 1);
+ mutex_unlock(&bts_tracer_mutex);
}
struct tracer bts_tracer __read_mostly =
{
.name = "hw-branch-tracer",
.init = bts_trace_init,
- .reset = bts_trace_stop,
+ .reset = bts_trace_reset,
.print_header = bts_trace_print_header,
.print_line = bts_trace_print_line,
.start = bts_trace_start,
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