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From: Tim Bird on 25 Feb 2010 18:40
Add support for tracing_thresh to the function_graph tracer. This
version of this feature isolates the checks into new entry and
return functions, to avoid adding more conditional code into the
main function_graph paths.

Also, add support for specifying tracing_thresh on the kernel
command line. When used like so: "tracing_thresh=200 ftrace=function_graph"
this can be used to analyse system startup. It is important to disable
tracing soon after boot, in order to avoid losing the trace data.

Note: the elimination of 'notrace' in the definition of '__init'
may be controversial. This can be removed, or made conditional,
if it's a bit too scary, but it worked OK for me. Tracing during
kernel startup still works, just with no visibility of routines
declared __init.

Signed-off-by: Tim Bird <tim.bird(a)am.sony.com>
---
include/linux/init.h | 2 +-
kernel/trace/trace.c | 20 ++++++++++++++++++--
kernel/trace/trace.h | 3 ++-
kernel/trace/trace_functions_graph.c | 32 +++++++++++++++++++++++++++++---
4 files changed, 50 insertions(+), 7 deletions(-)

--- a/include/linux/init.h
+++ b/include/linux/init.h
@@ -40,7 +40,7 @@

/* These are for everybody (although not all archs will actually
discard it in modules) */
-#define __init __section(.init.text) __cold notrace
+#define __init __section(.init.text) __cold
#define __initdata __section(.init.data)
#define __initconst __section(.init.rodata)
#define __exitdata __section(.exit.data)
--- a/kernel/trace/trace.c
+++ b/kernel/trace/trace.c
@@ -297,6 +297,21 @@ static int __init set_buf_size(char *str
}
__setup("trace_buf_size=", set_buf_size);

+static int __init set_tracing_thresh(char *str)
+{
+ unsigned long threshhold;
+ int ret;
+
+ if (!str)
+ return 0;
+ ret = strict_strtoul(str, 0, &threshhold);
+ if (ret < 0)
+ return 0;
+ tracing_thresh = threshhold * 1000;
+ return 1;
+}
+__setup("tracing_thresh=", set_tracing_thresh);
+
unsigned long nsecs_to_usecs(unsigned long nsecs)
{
return nsecs / 1000;
@@ -502,9 +517,10 @@ static ssize_t trace_seq_to_buffer(struc
static arch_spinlock_t ftrace_max_lock =
(arch_spinlock_t)__ARCH_SPIN_LOCK_UNLOCKED;

+unsigned long __read_mostly tracing_thresh;
+
#ifdef CONFIG_TRACER_MAX_TRACE
unsigned long __read_mostly tracing_max_latency;
-unsigned long __read_mostly tracing_thresh;

/*
* Copy the new maximum trace into the separate maximum-trace
@@ -4181,10 +4197,10 @@ static __init int tracer_init_debugfs(vo
#ifdef CONFIG_TRACER_MAX_TRACE
trace_create_file("tracing_max_latency", 0644, d_tracer,
&tracing_max_latency, &tracing_max_lat_fops);
+#endif

trace_create_file("tracing_thresh", 0644, d_tracer,
&tracing_thresh, &tracing_max_lat_fops);
-#endif

trace_create_file("README", 0444, d_tracer,
NULL, &tracing_readme_fops);
--- a/kernel/trace/trace.h
+++ b/kernel/trace/trace.h
@@ -396,9 +396,10 @@ extern int process_new_ksym_entry(char *

extern unsigned long nsecs_to_usecs(unsigned long nsecs);

+extern unsigned long tracing_thresh;
+
#ifdef CONFIG_TRACER_MAX_TRACE
extern unsigned long tracing_max_latency;
-extern unsigned long tracing_thresh;

void update_max_tr(struct trace_array *tr, struct task_struct *tsk, int cpu);
void update_max_tr_single(struct trace_array *tr,
--- a/kernel/trace/trace_functions_graph.c
+++ b/kernel/trace/trace_functions_graph.c
@@ -241,6 +241,14 @@ int trace_graph_entry(struct ftrace_grap
return ret;
}

+int trace_graph_thresh_entry(struct ftrace_graph_ent *trace)
+{
+ if (tracing_thresh)
+ return 1;
+ else
+ return trace_graph_entry(trace);
+}
+
static void __trace_graph_return(struct trace_array *tr,
struct ftrace_graph_ret *trace,
unsigned long flags,
@@ -287,13 +295,27 @@ void trace_graph_return(struct ftrace_gr
local_irq_restore(flags);
}

+void trace_graph_thresh_return(struct ftrace_graph_ret *trace)
+{
+ if (tracing_thresh &&
+ (trace->rettime - trace->calltime < tracing_thresh))
+ return;
+ else
+ trace_graph_return(trace);
+}
+
static int graph_trace_init(struct trace_array *tr)
{
int ret;

graph_array = tr;
- ret = register_ftrace_graph(&trace_graph_return,
- &trace_graph_entry);
+ if (tracing_thresh)
+ ret = register_ftrace_graph(&trace_graph_thresh_return,
+ &trace_graph_thresh_entry);
+ else
+ ret = register_ftrace_graph(&trace_graph_return,
+ &trace_graph_entry);
+
if (ret)
return ret;
tracing_start_cmdline_record();
@@ -891,7 +913,11 @@ print_graph_return(struct ftrace_graph_r
return TRACE_TYPE_PARTIAL_LINE;
}

- ret = trace_seq_printf(s, "}\n");
+ if (tracing_thresh) {
+ ret = trace_seq_printf(s, "} (%ps)\n", (void *)trace->func);
+ } else {
+ ret = trace_seq_printf(s, "}\n");
+ }
if (!ret)
return TRACE_TYPE_PARTIAL_LINE;



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