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>
diff --git a/kernel/trace/trace_irqsoff.c b/kernel/trace/trace_irqsoff.c
new file mode 100644
index 0000000..a9131b0
--- /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);