ftrace: trace irq disabled critical timings

This patch adds latency tracing for critical timings
(how long interrupts are disabled for).

 "irqsoff" is added to /debugfs/tracing/available_tracers

Note:
  tracing_max_latency
    also holds the max latency for irqsoff (in usecs).
   (default to large number so one must start latency tracing)

  tracing_thresh
    threshold (in usecs) to always print out if irqs off
    is detected to be longer than stated here.
    If irq_thresh is non-zero, then max_irq_latency
    is ignored.

Here's an example of a trace with ftrace_enabled = 0

=======
preemption latency trace v1.1.5 on 2.6.24-rc7
Signed-off-by: Ingo Molnar <mingo@elte.hu>
--------------------------------------------------------------------
 latency: 100 us, #3/3, CPU#1 | (M:rt VP:0, KP:0, SP:0 HP:0 #P:2)
    -----------------
    | task: swapper-0 (uid:0 nice:0 policy:0 rt_prio:0)
    -----------------
 => started at: _spin_lock_irqsave+0x2a/0xb7
 => ended at:   _spin_unlock_irqrestore+0x32/0x5f

                 _------=> CPU#
                / _-----=> irqs-off
               | / _----=> need-resched
               || / _---=> hardirq/softirq
               ||| / _--=> preempt-depth
               |||| /
               |||||     delay
   cmd     pid ||||| time  |   caller
      \   /    |||||   \   |   /
 swapper-0     1d.s3    0us+: _spin_lock_irqsave+0x2a/0xb7 (e1000_update_stats+0x47/0x64c [e1000])
 swapper-0     1d.s3  100us : _spin_unlock_irqrestore+0x32/0x5f (e1000_update_stats+0x641/0x64c [e1000])
 swapper-0     1d.s3  100us : trace_hardirqs_on_caller+0x75/0x89 (_spin_unlock_irqrestore+0x32/0x5f)

vim:ft=help
=======

And this is a trace with ftrace_enabled == 1

=======
preemption latency trace v1.1.5 on 2.6.24-rc7
--------------------------------------------------------------------
 latency: 102 us, #12/12, CPU#1 | (M:rt VP:0, KP:0, SP:0 HP:0 #P:2)
    -----------------
    | task: swapper-0 (uid:0 nice:0 policy:0 rt_prio:0)
    -----------------
 => started at: _spin_lock_irqsave+0x2a/0xb7
 => ended at:   _spin_unlock_irqrestore+0x32/0x5f

                 _------=> CPU#
                / _-----=> irqs-off
               | / _----=> need-resched
               || / _---=> hardirq/softirq
               ||| / _--=> preempt-depth
               |||| /
               |||||     delay
   cmd     pid ||||| time  |   caller
      \   /    |||||   \   |   /
 swapper-0     1dNs3    0us+: _spin_lock_irqsave+0x2a/0xb7 (e1000_update_stats+0x47/0x64c [e1000])
 swapper-0     1dNs3   46us : e1000_read_phy_reg+0x16/0x225 [e1000] (e1000_update_stats+0x5e2/0x64c [e1000])
 swapper-0     1dNs3   46us : e1000_swfw_sync_acquire+0x10/0x99 [e1000] (e1000_read_phy_reg+0x49/0x225 [e1000])
 swapper-0     1dNs3   46us : e1000_get_hw_eeprom_semaphore+0x12/0xa6 [e1000] (e1000_swfw_sync_acquire+0x36/0x99 [e1000])
 swapper-0     1dNs3   47us : __const_udelay+0x9/0x47 (e1000_read_phy_reg+0x116/0x225 [e1000])
 swapper-0     1dNs3   47us+: __delay+0x9/0x50 (__const_udelay+0x45/0x47)
 swapper-0     1dNs3   97us : preempt_schedule+0xc/0x84 (__delay+0x4e/0x50)
 swapper-0     1dNs3   98us : e1000_swfw_sync_release+0xc/0x55 [e1000] (e1000_read_phy_reg+0x211/0x225 [e1000])
 swapper-0     1dNs3   99us+: e1000_put_hw_eeprom_semaphore+0x9/0x35 [e1000] (e1000_swfw_sync_release+0x50/0x55 [e1000])
 swapper-0     1dNs3  101us : _spin_unlock_irqrestore+0xe/0x5f (e1000_update_stats+0x641/0x64c [e1000])
 swapper-0     1dNs3  102us : _spin_unlock_irqrestore+0x32/0x5f (e1000_update_stats+0x641/0x64c [e1000])
 swapper-0     1dNs3  102us : trace_hardirqs_on_caller+0x75/0x89 (_spin_unlock_irqrestore+0x32/0x5f)

vim:ft=help
=======

Signed-off-by: Steven Rostedt <srostedt@redhat.com>
Signed-off-by: Ingo Molnar <mingo@elte.hu>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>

1 files changed, 402 insertions, 0 deletions

diff --git a/kernel/trace/trace_irqsoff.c b/kernel/trace/trace_irqsoff.c
new file mode 100644
index 000000000000..a9131b0cf1a5
--- /dev/null
+++ b/kernel/trace/trace_irqsoff.c
@@ -0,0 +1,402 @@
+/*
+ * trace irqs off criticall timings
+ *
+ * Copyright (C) 2007-2008 Steven Rostedt <srostedt@redhat.com>
+ * Copyright (C) 2008 Ingo Molnar <mingo@redhat.com>
+ *
+ * From code in the latency_tracer, that is:
+ *
+ *  Copyright (C) 2004-2006 Ingo Molnar
+ *  Copyright (C) 2004 William Lee Irwin III
+ */
+#include <linux/kallsyms.h>
+#include <linux/debugfs.h>
+#include <linux/uaccess.h>
+#include <linux/module.h>
+#include <linux/ftrace.h>
+#include <linux/fs.h>
+
+#include "trace.h"
+
+static struct trace_array               *irqsoff_trace __read_mostly;
+static int                              tracer_enabled __read_mostly;
+
+/*
+ * Sequence count - we record it when starting a measurement and
+ * skip the latency if the sequence has changed - some other section
+ * did a maximum and could disturb our measurement with serial console
+ * printouts, etc. Truly coinciding maximum latencies should be rare
+ * and what happens together happens separately as well, so this doesnt
+ * decrease the validity of the maximum found:
+ */
+static __cacheline_aligned_in_smp       unsigned long max_sequence;
+
+#ifdef CONFIG_FTRACE
+/*
+ * irqsoff uses its own tracer function to keep the overhead down:
+ */
+static void notrace
+irqsoff_tracer_call(unsigned long ip, unsigned long parent_ip)
+{
+        struct trace_array *tr = irqsoff_trace;
+        struct trace_array_cpu *data;
+        unsigned long flags;
+        long disabled;
+        int cpu;
+
+        if (likely(!tracer_enabled))
+                return;
+
+        local_save_flags(flags);
+
+        if (!irqs_disabled_flags(flags))
+                return;
+
+        cpu = raw_smp_processor_id();
+        data = tr->data[cpu];
+        disabled = atomic_inc_return(&data->disabled);
+
+        if (likely(disabled == 1))
+                ftrace(tr, data, ip, parent_ip, flags);
+
+        atomic_dec(&data->disabled);
+}
+
+static struct ftrace_ops trace_ops __read_mostly =
+{
+        .func = irqsoff_tracer_call,
+};
+#endif /* CONFIG_FTRACE */
+
+/*
+ * Should this new latency be reported/recorded?
+ */
+static int notrace report_latency(cycle_t delta)
+{
+        if (tracing_thresh) {
+                if (delta < tracing_thresh)
+                        return 0;
+        } else {
+                if (delta <= tracing_max_latency)
+                        return 0;
+        }
+        return 1;
+}
+
+static void notrace
+check_critical_timing(struct trace_array *tr,
+                      struct trace_array_cpu *data,
+                      unsigned long parent_ip,
+                      int cpu)
+{
+        unsigned long latency, t0, t1;
+        cycle_t T0, T1, T2, delta;
+        unsigned long flags;
+
+        /*
+         * usecs conversion is slow so we try to delay the conversion
+         * as long as possible:
+         */
+        T0 = data->preempt_timestamp;
+        T1 = now(cpu);
+        delta = T1-T0;
+
+        local_save_flags(flags);
+
+        if (!report_latency(delta))
+                goto out;
+
+        ftrace(tr, data, CALLER_ADDR0, parent_ip, flags);
+        /*
+         * Update the timestamp, because the trace entry above
+         * might change it (it can only get larger so the latency
+         * is fair to be reported):
+         */
+        T2 = now(cpu);
+
+        delta = T2-T0;
+
+        latency = nsecs_to_usecs(delta);
+
+        if (data->critical_sequence != max_sequence)
+                goto out;
+
+        tracing_max_latency = delta;
+        t0 = nsecs_to_usecs(T0);
+        t1 = nsecs_to_usecs(T1);
+
+        data->critical_end = parent_ip;
+
+        update_max_tr_single(tr, current, cpu);
+
+        if (tracing_thresh)
+                printk(KERN_INFO "(%16s-%-5d|#%d): %lu us critical section "
+                       "violates %lu us threshold.\n"
+                       " => started at timestamp %lu: ",
+                                current->comm, current->pid,
+                                raw_smp_processor_id(),
+                                latency, nsecs_to_usecs(tracing_thresh), t0);
+        else
+                printk(KERN_INFO "(%16s-%-5d|#%d):"
+                       " new %lu us maximum-latency "
+                       "critical section.\n => started at timestamp %lu: ",
+                                current->comm, current->pid,
+                                raw_smp_processor_id(),
+                                latency, t0);
+
+        print_symbol(KERN_CONT "<%s>\n", data->critical_start);
+        printk(KERN_CONT " =>   ended at timestamp %lu: ", t1);
+        print_symbol(KERN_CONT "<%s>\n", data->critical_end);
+        dump_stack();
+        t1 = nsecs_to_usecs(now(cpu));
+        printk(KERN_CONT " =>   dump-end timestamp %lu\n\n", t1);
+
+        max_sequence++;
+
+out:
+        data->critical_sequence = max_sequence;
+        data->preempt_timestamp = now(cpu);
+        tracing_reset(data);
+        ftrace(tr, data, CALLER_ADDR0, parent_ip, flags);
+}
+
+static inline void notrace
+start_critical_timing(unsigned long ip, unsigned long parent_ip)
+{
+        int cpu;
+        struct trace_array *tr = irqsoff_trace;
+        struct trace_array_cpu *data;
+        unsigned long flags;
+
+        if (likely(!tracer_enabled))
+                return;
+
+        cpu = raw_smp_processor_id();
+        data = tr->data[cpu];
+
+        if (unlikely(!data) || unlikely(!data->trace) ||
+            data->critical_start || atomic_read(&data->disabled))
+                return;
+
+        atomic_inc(&data->disabled);
+
+        data->critical_sequence = max_sequence;
+        data->preempt_timestamp = now(cpu);
+        data->critical_start = parent_ip;
+        tracing_reset(data);
+
+        local_save_flags(flags);
+        ftrace(tr, data, ip, parent_ip, flags);
+
+        atomic_dec(&data->disabled);
+}
+
+static inline void notrace
+stop_critical_timing(unsigned long ip, unsigned long parent_ip)
+{
+        int cpu;
+        struct trace_array *tr = irqsoff_trace;
+        struct trace_array_cpu *data;
+        unsigned long flags;
+
+        if (likely(!tracer_enabled))
+                return;
+
+        cpu = raw_smp_processor_id();
+        data = tr->data[cpu];
+
+        if (unlikely(!data) || unlikely(!data->trace) ||
+            !data->critical_start || atomic_read(&data->disabled))
+                return;
+
+        atomic_inc(&data->disabled);
+        local_save_flags(flags);
+        ftrace(tr, data, ip, parent_ip, flags);
+        check_critical_timing(tr, data, parent_ip, cpu);
+        data->critical_start = 0;
+        atomic_dec(&data->disabled);
+}
+
+void notrace start_critical_timings(void)
+{
+        unsigned long flags;
+
+        local_save_flags(flags);
+
+        if (irqs_disabled_flags(flags))
+                start_critical_timing(CALLER_ADDR0, CALLER_ADDR1);
+}
+
+void notrace stop_critical_timings(void)
+{
+        unsigned long flags;
+
+        local_save_flags(flags);
+
+        if (irqs_disabled_flags(flags))
+                stop_critical_timing(CALLER_ADDR0, CALLER_ADDR1);
+}
+
+#ifdef CONFIG_PROVE_LOCKING
+void notrace time_hardirqs_on(unsigned long a0, unsigned long a1)
+{
+        unsigned long flags;
+
+        local_save_flags(flags);
+
+        if (irqs_disabled_flags(flags))
+                stop_critical_timing(a0, a1);
+}
+
+void notrace time_hardirqs_off(unsigned long a0, unsigned long a1)
+{
+        unsigned long flags;
+
+        local_save_flags(flags);
+
+        if (irqs_disabled_flags(flags))
+                start_critical_timing(a0, a1);
+}
+
+#else /* !CONFIG_PROVE_LOCKING */
+
+/*
+ * Stubs:
+ */
+
+void early_boot_irqs_off(void)
+{
+}
+
+void early_boot_irqs_on(void)
+{
+}
+
+void trace_softirqs_on(unsigned long ip)
+{
+}
+
+void trace_softirqs_off(unsigned long ip)
+{
+}
+
+inline void print_irqtrace_events(struct task_struct *curr)
+{
+}
+
+/*
+ * We are only interested in hardirq on/off events:
+ */
+void notrace trace_hardirqs_on(void)
+{
+        unsigned long flags;
+
+        local_save_flags(flags);
+
+        if (irqs_disabled_flags(flags))
+                stop_critical_timing(CALLER_ADDR0, CALLER_ADDR1);
+}
+EXPORT_SYMBOL(trace_hardirqs_on);
+
+void notrace trace_hardirqs_off(void)
+{
+        unsigned long flags;
+
+        local_save_flags(flags);
+
+        if (irqs_disabled_flags(flags))
+                start_critical_timing(CALLER_ADDR0, CALLER_ADDR1);
+}
+EXPORT_SYMBOL(trace_hardirqs_off);
+
+void notrace trace_hardirqs_on_caller(unsigned long caller_addr)
+{
+        unsigned long flags;
+
+        local_save_flags(flags);
+
+        if (irqs_disabled_flags(flags))
+                stop_critical_timing(CALLER_ADDR0, caller_addr);
+}
+EXPORT_SYMBOL(trace_hardirqs_on_caller);
+
+void notrace trace_hardirqs_off_caller(unsigned long caller_addr)
+{
+        unsigned long flags;
+
+        local_save_flags(flags);
+
+        if (irqs_disabled_flags(flags))
+                start_critical_timing(CALLER_ADDR0, caller_addr);
+}
+EXPORT_SYMBOL(trace_hardirqs_off_caller);
+
+#endif /* CONFIG_PROVE_LOCKING */
+
+static void start_irqsoff_tracer(struct trace_array *tr)
+{
+        tracer_enabled = 1;
+        register_ftrace_function(&trace_ops);
+}
+
+static void stop_irqsoff_tracer(struct trace_array *tr)
+{
+        unregister_ftrace_function(&trace_ops);
+        tracer_enabled = 0;
+}
+
+static void irqsoff_tracer_init(struct trace_array *tr)
+{
+        irqsoff_trace = tr;
+        /* make sure that the tracer is visibel */
+        smp_wmb();
+
+        if (tr->ctrl)
+                start_irqsoff_tracer(tr);
+}
+
+static void irqsoff_tracer_reset(struct trace_array *tr)
+{
+        if (tr->ctrl)
+                stop_irqsoff_tracer(tr);
+}
+
+static void irqsoff_tracer_ctrl_update(struct trace_array *tr)
+{
+        if (tr->ctrl)
+                start_irqsoff_tracer(tr);
+        else
+                stop_irqsoff_tracer(tr);
+}
+
+static void notrace irqsoff_tracer_open(struct trace_iterator *iter)
+{
+        /* stop the trace while dumping */
+        if (iter->tr->ctrl)
+                stop_irqsoff_tracer(iter->tr);
+}
+
+static void notrace irqsoff_tracer_close(struct trace_iterator *iter)
+{
+        if (iter->tr->ctrl)
+                start_irqsoff_tracer(iter->tr);
+}
+
+static struct tracer irqsoff_tracer __read_mostly =
+{
+        .name           = "irqsoff",
+        .init           = irqsoff_tracer_init,
+        .reset          = irqsoff_tracer_reset,
+        .open           = irqsoff_tracer_open,
+        .close          = irqsoff_tracer_close,
+        .ctrl_update    = irqsoff_tracer_ctrl_update,
+        .print_max      = 1,
+};
+
+__init static int init_irqsoff_tracer(void)
+{
+        register_tracer(&irqsoff_tracer);
+
+        return 0;
+}
+device_initcall(init_irqsoff_tracer);