MIPS, Tracing: Speed up function graph tracer

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 comparison.

Signed-off-by: Wu Zhangjin <wuzhangjin@gmail.com>
Cc: Steven Rostedt <srostedt@redhat.com>
Cc: linux-mips@linux-mips.org
Patchwork: https://patchwork.linux-mips.org/patch/2006/
Signed-off-by: Ralf Baechle <ralf@duck.linux-mips.net>

diff --git a/arch/mips/kernel/ftrace.c b/arch/mips/kernel/ftrace.c
index 5a84a1f..635c1dc 100644 (file)
--- 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);