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Message-ID: <5549B533.5070609@bmw-carit.de>
Date: Wed, 6 May 2015 08:31:15 +0200
From: Daniel Wagner <daniel.wagner@...-carit.de>
To: Daniel Wagner <daniel.wagner@...-carit.de>,
Steven Rostedt <rostedt@...dmis.org>
CC: Ingo Molnar <mingo@...hat.com>,
Tom Zanussi <tom.zanussi@...ux.intel.com>,
Carsten Emde <C.Emde@...dl.org>,
<linux-rt-users@...r.kernel.org>, <linux-kernel@...r.kernel.org>
Subject: Re: [RFD 5/5] tracing: Add trace_irqsoff tracepoints
It is possible to avoid the hackery from patch 4 completely.
If the tracepoint is placed in stop_critical_timing(),
lockdep doesn't complain anymore.
I have changed this patch so that I don't do need to any additional
work to get the latency calculated. Instead just use the values
from check_critical_timing().
That means the tracepoints will only be hit if the tracer
preemptirqsoff & co is enabled. Instead having several
different tracepoints just add the a new field which describes where
the latency is coming from. Furthermore, this approach also avoids
adding additional overhead when the tracers are compiled in but
not used.
# cat /sys/kernel/debug/tracing/events/latency/latency/format
name: latency
ID: 333
format:
field:unsigned short common_type; offset:0; size:2; signed:0;
field:unsigned char common_flags; offset:2; size:1; signed:0;
field:unsigned char common_preempt_count; offset:3; size:1; signed:0;
field:int common_pid; offset:4; size:4; signed:1;
field:int source; offset:8; size:4; signed:1;
field:cycles_t latency; offset:16; size:8; signed:0;
print fmt: "source=%s latency=%llu", __print_symbolic(REC->source, {1, "critical section" }, {2, "irq"}, {3, "preempt"}), REC->latency
So in short you could do following to get a histogram:
# echo preemptirqsoff > /sys/kernel/debug/tracing/current_tracer
# echo 1 > /sys/kernel/debug/tracing/tracing_on
# echo 'hist:key=latency.bucket:val=hitcount:sort=latency ' \
'if source == 1' > \
/sys/kernel/debug/tracing/events/latency/latency/trigger
# cat /sys/kernel/debug/tracing/events/latency/latency/hist | head -20
# trigger info: hist:keys=latency.bucket:vals=:sort=latency.bucket:size=2048 if source == 1 [active]
latency: 1792 hitcount: 7
latency: 2048 hitcount: 23
latency: 2304 hitcount: 37
latency: 2560 hitcount: 57
latency: 2816 hitcount: 33
latency: 3072 hitcount: 40
latency: 3328 hitcount: 16
latency: 3584 hitcount: 40
latency: 3840 hitcount: 133
latency: 4096 hitcount: 150
latency: 4352 hitcount: 196
latency: 4608 hitcount: 338
latency: 4864 hitcount: 159
latency: 5120 hitcount: 92
latency: 5376 hitcount: 58
latency: 5632 hitcount: 26
latency: 5888 hitcount: 25
latency: 6144 hitcount: 24
I do some more testing to see if I missed something.
cheers,
daniel
>From 449c6881425cc461dd7ea6b6f865d2efe99175b3 Mon Sep 17 00:00:00 2001
From: Daniel Wagner <daniel.wagner@...-carit.de>
Date: Wed, 29 Apr 2015 17:09:04 +0200
Subject: [PATCH] tracing: Add trace_irqsoff tracepoints
In order to create latency histograms, we place a tracepoint at the end
of critical section.
Not for inclusion!
Not-Signed-off-by: Daniel Wagner <daniel.wagner@...-carit.de>
---
include/trace/events/latency.h | 41 +++++++++++++++++++++++++++++++++++++++++
kernel/trace/trace_irqsoff.c | 22 ++++++++++++++--------
2 files changed, 55 insertions(+), 8 deletions(-)
create mode 100644 include/trace/events/latency.h
diff --git a/include/trace/events/latency.h b/include/trace/events/latency.h
new file mode 100644
index 0000000..1ed8b13
--- /dev/null
+++ b/include/trace/events/latency.h
@@ -0,0 +1,41 @@
+#undef TRACE_SYSTEM
+#define TRACE_SYSTEM latency
+
+#if !defined(_TRACE_LATENCY_H) || defined(TRACE_HEADER_MULTI_READ)
+#define _TRACE_LATENCY_H
+
+#include <linux/tracepoint.h>
+
+#define LATENCY_CS 1
+#define LATENCY_IRQ 2
+#define LATENCY_PREEMPT 3
+
+#define latency_source_sym \
+ {LATENCY_CS, "critical section" }, \
+ {LATENCY_IRQ, "irq"}, \
+ {LATENCY_PREEMPT, "preempt"}
+
+TRACE_EVENT(latency,
+ TP_PROTO(int source, cycles_t latency),
+
+ TP_ARGS(source, latency),
+
+ TP_STRUCT__entry(
+ __field(int, source)
+ __field(cycles_t, latency)
+ ),
+
+ TP_fast_assign(
+ __entry->source = source;
+ __entry->latency = latency;
+ ),
+
+ TP_printk("source=%s latency=%llu",
+ __print_symbolic(__entry->source, latency_source_sym),
+ __entry->latency)
+);
+
+#endif /* _TRACE_LATENCY_H */
+
+/* This part must be outside protection */
+#include <trace/define_trace.h>
diff --git a/kernel/trace/trace_irqsoff.c b/kernel/trace/trace_irqsoff.c
index 8523ea3..7a1d254 100644
--- a/kernel/trace/trace_irqsoff.c
+++ b/kernel/trace/trace_irqsoff.c
@@ -14,8 +14,13 @@
#include <linux/module.h>
#include <linux/ftrace.h>
+#include <trace/events/sched.h>
+
#include "trace.h"
+#define CREATE_TRACE_POINTS
+#include <trace/events/latency.h>
+
static struct trace_array *irqsoff_trace __read_mostly;
static int tracer_enabled __read_mostly;
@@ -311,7 +316,7 @@ static void
check_critical_timing(struct trace_array *tr,
struct trace_array_cpu *data,
unsigned long parent_ip,
- int cpu)
+ int cpu, int source)
{
cycle_t T0, T1, delta;
unsigned long flags;
@@ -325,6 +330,7 @@ check_critical_timing(struct trace_array *tr,
pc = preempt_count();
+ trace_latency(source, delta);
if (!report_latency(tr, delta))
goto out;
@@ -396,7 +402,7 @@ start_critical_timing(unsigned long ip, unsigned long parent_ip)
}
static inline void
-stop_critical_timing(unsigned long ip, unsigned long parent_ip)
+stop_critical_timing(unsigned long ip, unsigned long parent_ip, int source)
{
int cpu;
struct trace_array *tr = irqsoff_trace;
@@ -423,7 +429,7 @@ stop_critical_timing(unsigned long ip, unsigned long parent_ip)
local_save_flags(flags);
__trace_function(tr, ip, parent_ip, flags, preempt_count());
- check_critical_timing(tr, data, parent_ip ? : ip, cpu);
+ check_critical_timing(tr, data, parent_ip ? : ip, cpu, source);
data->critical_start = 0;
atomic_dec(&data->disabled);
}
@@ -439,7 +445,7 @@ EXPORT_SYMBOL_GPL(start_critical_timings);
void stop_critical_timings(void)
{
if (preempt_trace() || irq_trace())
- stop_critical_timing(CALLER_ADDR0, CALLER_ADDR1);
+ stop_critical_timing(CALLER_ADDR0, CALLER_ADDR1, LATENCY_CS);
}
EXPORT_SYMBOL_GPL(stop_critical_timings);
@@ -448,7 +454,7 @@ EXPORT_SYMBOL_GPL(stop_critical_timings);
void time_hardirqs_on(unsigned long a0, unsigned long a1)
{
if (!preempt_trace() && irq_trace())
- stop_critical_timing(a0, a1);
+ stop_critical_timing(a0, a1, LATENCY_IRQ);
}
void time_hardirqs_off(unsigned long a0, unsigned long a1)
@@ -481,7 +487,7 @@ inline void print_irqtrace_events(struct task_struct *curr)
void trace_hardirqs_on(void)
{
if (!preempt_trace() && irq_trace())
- stop_critical_timing(CALLER_ADDR0, CALLER_ADDR1);
+ stop_critical_timing(CALLER_ADDR0, CALLER_ADDR1, LATENCY_IRQ);
}
EXPORT_SYMBOL(trace_hardirqs_on);
@@ -495,7 +501,7 @@ EXPORT_SYMBOL(trace_hardirqs_off);
__visible void trace_hardirqs_on_caller(unsigned long caller_addr)
{
if (!preempt_trace() && irq_trace())
- stop_critical_timing(CALLER_ADDR0, caller_addr);
+ stop_critical_timing(CALLER_ADDR0, caller_addr, LATENCY_IRQ);
}
EXPORT_SYMBOL(trace_hardirqs_on_caller);
@@ -513,7 +519,7 @@ EXPORT_SYMBOL(trace_hardirqs_off_caller);
void trace_preempt_on(unsigned long a0, unsigned long a1)
{
if (preempt_trace() && !irq_trace())
- stop_critical_timing(a0, a1);
+ stop_critical_timing(a0, a1, LATENCY_PREEMPT);
}
void trace_preempt_off(unsigned long a0, unsigned long a1)
--
2.1.0
--
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