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[PATCH 1/5] tracing, MIPS: Speed up function graph tracer

To: Ralf Baechle <ralf@linux-mips.org>
Subject: [PATCH 1/5] tracing, MIPS: Speed up function graph tracer
From: Wu Zhangjin <wuzhangjin@gmail.com>
Date: Thu, 20 Jan 2011 03:28:27 +0800
Cc: Wu Zhangjin <wuzhangjin@gmail.com>, Steven Rostedt <srostedt@redhat.com>, linux-mips@linux-mips.org
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This simply moves the "ip-=4" statement down to the end of the do { ...
} while (...); loop, which reduces one unneeded subtration and the
subsequent memory loading and comparation. as a result, speed up the
function a little.

Signed-off-by: Wu Zhangjin <wuzhangjin@gmail.com>
---
 arch/mips/kernel/ftrace.c |   14 +++++++-------
 1 files changed, 7 insertions(+), 7 deletions(-)

diff --git a/arch/mips/kernel/ftrace.c b/arch/mips/kernel/ftrace.c
index 5a84a1f..635c1dc 100644
--- a/arch/mips/kernel/ftrace.c
+++ b/arch/mips/kernel/ftrace.c
@@ -200,19 +200,17 @@ unsigned long ftrace_get_parent_addr(unsigned long 
self_addr,
        int faulted;
 
        /*
-        * For module, move the ip from calling site of mcount to the
-        * instruction "lui v1, hi_16bit_of_mcount"(offset is 20), but for
-        * kernel, move to the instruction "move ra, at"(offset is 12)
+        * For module, move the ip from calling site of mcount after the
+        * instruction "lui v1, hi_16bit_of_mcount"(offset is 24), but for
+        * kernel, move after the instruction "move ra, at"(offset is 16)
         */
-       ip = self_addr - (in_module(self_addr) ? 20 : 12);
+       ip = self_addr - (in_module(self_addr) ? 24 : 16);
 
        /*
         * search the text until finding the non-store instruction or "s{d,w}
         * ra, offset(sp)" instruction
         */
        do {
-               ip -= 4;
-
                /* get the code at "ip": code = *(unsigned int *)ip; */
                safe_load_code(code, ip, faulted);
 
@@ -226,7 +224,9 @@ unsigned long ftrace_get_parent_addr(unsigned long 
self_addr,
                if ((code & S_R_SP) != S_R_SP)
                        return parent_addr;
 
-       } while (((code & S_RA_SP) != S_RA_SP));
+               /* Move to the next instruction */
+               ip -= 4;
+       } while ((code & S_RA_SP) != S_RA_SP);
 
        sp = fp + (code & OFFSET_MASK);
 
-- 
1.7.1


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