linux-kernel - [PATCH 4.9 36/94] sparc/ftrace: Fix ftrace graph time measurement

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Date:   Mon,  5 Jun 2017 18:17:12 +0200
From:   Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:     linux-kernel@...r.kernel.org
Cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        stable@...r.kernel.org,
        "Liam R. Howlett" <Liam.Howlett@...cle.com>,
        "David S. Miller" <davem@...emloft.net>
Subject: [PATCH 4.9 36/94] sparc/ftrace: Fix ftrace graph time measurement

4.9-stable review patch.  If anyone has any objections, please let me know.

------------------

From: "Liam R. Howlett" <Liam.Howlett@...cle.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@...cle.com>
Signed-off-by: David S. Miller <davem@...emloft.net>
Signed-off-by: Greg Kroah-Hartman <gregkh@...uxfoundation.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;
 }