[PATCH] perf bench: add --prefault option for causing page faults before benchmark

[Hitoshi Mitake <mitake@dcl.info.waseda.ac.jp>]

This patch adds --prefault option to perf bench mem memcpy.
If user specify this option to perf bench mem memcpy, overhead of
page faults will be removed from the score of memcpy().

Example of usage:
| % ./perf bench mem memcpy -l 500MB
| # Running mem/memcpy benchmark...
| # Copying 500MB Bytes from 0x7fc036749010 to 0x7fc055b4a010 ...
|
|      628.526821 MB/Sec
| mitake@X201i:~/linux/.../tools/perf% ./perf bench mem memcpy -l 500MB --prefault
| # Running mem/memcpy benchmark...
| # Copying 500MB Bytes from 0x7ff1b45e2010 to 0x7ff1d39e3010 ...
|
|        4.849256 GB/Sec

Signed-off-by: Hitoshi Mitake <mitake@dcl.info.waseda.ac.jp>
Cc: Ma Ling <ling.ma@intel.com>
Cc: Zhao Yakui <yakui.zhao@intel.com>
Cc: Peter Zijlstra <a.p.zijlstra@chello.nl>
Cc: Arnaldo Carvalho de Melo <acme@redhat.com>
Cc: Paul Mackerras <paulus@samba.org>
Cc: Frederic Weisbecker <fweisbec@gmail.com>
Cc: Steven Rostedt <rostedt@goodmis.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: H. Peter Anvin <hpa@zytor.com>
---
 tools/perf/bench/mem-memcpy.c |    9 ++++++++-
 1 files changed, 8 insertions(+), 1 deletions(-)

diff --git a/tools/perf/bench/mem-memcpy.c b/tools/perf/bench/mem-memcpy.c
index 38dae74..be31ddb 100644
--- a/tools/perf/bench/mem-memcpy.c
+++ b/tools/perf/bench/mem-memcpy.c
@@ -23,8 +23,9 @@
 
 static const char	*length_str	= "1MB";
 static const char	*routine	= "default";
-static bool		use_clock	= false;
+static bool		use_clock;
 static int		clock_fd;
+static bool		prefault;
 
 static const struct option options[] = {
 	OPT_STRING('l', "length", &length_str, "1MB",
@@ -34,6 +35,8 @@ static const struct option options[] = {
 		    "Specify routine to copy"),
 	OPT_BOOLEAN('c', "clock", &use_clock,
 		    "Use CPU clock for measuring"),
+	OPT_BOOLEAN('p', "prefault", &prefault,
+		    "Cause page faults before memcpy()"),
 	OPT_END()
 };
 
@@ -139,6 +142,10 @@ int bench_mem_memcpy(int argc, const char **argv,
 		       length_str, src, dst);
 	}
 
+
+	if (prefault)
+		routines[i].fn(dst, src, length);
+
 	if (use_clock) {
 		init_clock();
 		clock_start = get_clock();
-- 
1.7.1.1