x86, ftrace, hw-branch-tracer: support hotplug cpus

Support hotplug cpus.

Reported-by: Andi Kleen <ak@linux.intel.com>
Signed-off-by: Markus Metzger <markus.t.metzger@intel.com>
Signed-off-by: Steven Rostedt <srostedt@redhat.com>
Signed-off-by: Ingo Molnar <mingo@elte.hu>

1 files changed, 107 insertions, 16 deletions

diff --git a/kernel/trace/trace_hw_branches.c b/kernel/trace/trace_hw_branches.c
index df21c1e72b95..398195397c75 100644
--- a/kernel/trace/trace_hw_branches.c
+++ b/kernel/trace/trace_hw_branches.c
@@ -1,7 +1,8 @@
 /*
  * h/w branch tracer for x86 based on bts
  *
- * Copyright (C) 2008 Markus Metzger <markus.t.metzger@gmail.com>
+ * Copyright (C) 2008-2009 Intel Corporation.
+ * Markus Metzger <markus.t.metzger@gmail.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>
 
@@ -19,13 +23,31 @@
 
 #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)
@@ -43,14 +65,20 @@ static void bts_trace_start_cpu(void *arg)
 
 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(cpu, cpu_possible_mask)
-                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) {
@@ -61,20 +89,58 @@ static void bts_trace_stop_cpu(void *arg)
 
 static void bts_trace_stop(struct trace_array *tr)
 {
-        int cpu;
+        mutex_lock(&bts_tracer_mutex);
+
+        trace_hw_branches_enabled = 0;
+        on_each_cpu(bts_trace_stop_cpu, NULL, 1);
 
-        for_each_cpu(cpu, cpu_possible_mask)
+        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,
@@ -108,18 +174,34 @@ void trace_hw_branch(struct trace_array *tr, u64 from, u64 to)
 {
         struct ring_buffer_event *event;
         struct hw_branch_entry *entry;
-        unsigned long irq;
+        unsigned long irq1, irq2;
+        int cpu;
 
-        event = ring_buffer_lock_reserve(tr->buffer, sizeof(*entry), &irq);
-        if (!event)
+        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), &irq2);
+        if (!event)
+                goto out;
         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,
@@ -143,6 +225,11 @@ static void trace_bts_at(struct trace_array *tr,
         }
 }
 
+/*
+ * 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;
@@ -152,6 +239,9 @@ static void trace_bts_cpu(void *arg)
         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)
@@ -171,17 +261,18 @@ out:
 
 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(cpu, cpu_possible_mask)
-                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,