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SubjectRe: [GIT PULL] x86/cpu changes for v2.6.34
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On Mon, 2010-03-01 at 14:42 -0500, Steven Rostedt wrote:

> As Frederic has said you can use 'ftrace=function_graph' on the kernel
> command line. It will be initialized in early_initcall (which I believe
> is before CPUs are set up. Then add a tracing_off() after the trouble
> code. You can make the trace buffers bigger with the kernel command
> line:
>
> trace_buf_size=10000000
>
> The above will make the trace buffer 10Meg per CPU. Unlike the
> "buffer_size_kb" file, this number is in bytes, even though it will
> round to the nearest page. (I probably should make this into kb, and
> rename it to trace_buf_size_kb, and deprecate trace_buf_size).
>
> Then you can cat out /debug/tracing/trace, and search for large
> latencies in the timestamps.

I just tried the above and it doesn't work. The ring buffer gets
allocated with the early_initcall(), so trace_printk()'s will work. But
the function and function graph tracers don't get registered until the
device_initcall().

If you are still interested, this patch will allow you to run the
function graph tracer before smp_init(). You still need to add
"ftrace=function_graph" on the kernel command line.

It's a hack, but I tried it out and it worked.

-- Steve



diff --git a/init/main.c b/init/main.c
index 4cb47a1..b334663 100644
--- a/init/main.c
+++ b/init/main.c
@@ -868,8 +868,15 @@ static int __init kernel_init(void * unused)
do_pre_smp_initcalls();
start_boot_trace();

+ {
+ int init_graph_trace(void);
+ init_graph_trace();
+ }
+ trace_printk("start\n");
smp_init();
sched_init_smp();
+ trace_printk("end\n");
+ tracing_off();

do_basic_setup();

diff --git a/kernel/trace/trace_functions_graph.c b/kernel/trace/trace_functions_graph.c
index aaf580c..f18cad8 100644
--- a/kernel/trace/trace_functions_graph.c
+++ b/kernel/trace/trace_functions_graph.c
@@ -1214,11 +1214,11 @@ static struct tracer graph_trace __read_mostly = {
#endif
};

-static __init int init_graph_trace(void)
+__init int init_graph_trace(void)
{
max_bytes_for_cpu = snprintf(NULL, 0, "%d", nr_cpu_ids - 1);

return register_tracer(&graph_trace);
}

-device_initcall(init_graph_trace);
+//device_initcall(init_graph_trace);



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