[PATCH 4.11 044/115] sparc/ftrace: Fix ftrace graph time measurement

Greg Kroah-Hartman
2017-06-05T16:29:56Z

From: "Liam R. Howlett" <Liam.Howlett@Oracle.com>

[ Upstream commit 48078d2dac0a26f84f5f3ec704f24f7c832cce14 ]

The ftrace function_graph time measurements of a given function is not
accurate according to those recorded by ftrace using the function
filters. This change pulls the x86_64 fix from 'commit 722b3c746953
("ftrace/graph: Trace function entry before updating index")' into the
sparc specific prepare_ftrace_return which stops ftrace from
counting interrupted tasks in the time measurement.

Example measurements for select_task_rq_fair running "hackbench 100
process 1000":

| tracing/trace_stat/function0 | function_graph
Before patch | 2.802 us | 4.255 us
After patch | 2.749 us | 3.094 us

Signed-off-by: Liam R. Howlett <Liam.Howlett@Oracle.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
---
arch/sparc/kernel/ftrace.c | 13 ++++++-------
1 file changed, 6 insertions(+), 7 deletions(-)

--- a/arch/sparc/kernel/ftrace.c
+++ b/arch/sparc/kernel/ftrace.c
@@ -130,17 +130,16 @@ unsigned long prepare_ftrace_return(unsi
if (unlikely(atomic_read(&current->tracing_graph_pause)))
return parent + 8UL;

- if (ftrace_push_return_trace(parent, self_addr, &trace.depth,
- frame_pointer, NULL) == -EBUSY)
- return parent + 8UL;
-
trace.func = self_addr;
+ trace.depth = current->curr_ret_stack + 1;

/* Only trace if the calling function expects to */
- if (!ftrace_graph_entry(&trace)) {
- current->curr_ret_stack--;
+ if (!ftrace_graph_entry(&trace))
+ return parent + 8UL;
+
+ if (ftrace_push_return_trace(parent, self_addr, &trace.depth,
+ frame_pointer, NULL) == -EBUSY)
return parent + 8UL;
- }

return return_hooker;
}