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[PATCH] MIPS: tracing/ftrace: Speedup a little for function graph tracer

To: linux-mips@linux-mips.org, ralf@linux-mips.org
Subject: [PATCH] MIPS: tracing/ftrace: Speedup a little for function graph tracer
From: Wu Zhangjin <wuzhangjin@gmail.com>
Date: Sat, 23 Oct 2010 04:57:01 +0800
Cc: David Daney <ddaney@caviumnetworks.com>, rostedt@goodmis.org, Wu Zhangjin <wuzhangjin@gmail.com>
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From: Wu Zhangjin <wuzhangjin@gmail.com>

This patch removes one "ip -= 4" instruction via the following change:

        ip = x;                         ip = x - 4;

        do {                            do {
                ip -= 4;        ==>             foo(ip);
                foo(ip);                        ...
                ...                             ip -= 4;
        } while (y);                    } while (y);

BTW, the "while (( ))" is cleaned up to "while ()".

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..65f1949 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 previous instruction position */
+               ip -= 4;
+       } while ((code & S_RA_SP) != S_RA_SP);
 
        sp = fp + (code & OFFSET_MASK);
 
-- 
1.7.1


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