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authorOndrej Bilka <neleai@seznam.cz>2013-05-08 08:21:05 +0200
committerOndrej Bilka <neleai@seznam.cz>2013-05-08 08:25:08 +0200
commitbb7cf681e90d5aa2d867aeff4948ac605447de7d (patch)
treeac1b16c1eb024734fdddebee2bb051d7b2c8389b /benchtests
parentba8539473296645ef5e710e506534682f9eb5572 (diff)
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Preheat CPU in benchtests.
A benchmark could be skewed by CPU initialy working on minimal frequency and speeding up later. We first run code in loop to partialy fix this issue.
Diffstat (limited to 'benchtests')
-rw-r--r--benchtests/bench-skeleton.c17
1 files changed, 17 insertions, 0 deletions
diff --git a/benchtests/bench-skeleton.c b/benchtests/bench-skeleton.c
index 7359184..a13ad02 100644
--- a/benchtests/bench-skeleton.c
+++ b/benchtests/bench-skeleton.c
@@ -22,6 +22,21 @@
#include <time.h>
#include <inttypes.h>
+volatile unsigned int dontoptimize = 0;
+void startup ()
+{
+ /* This loop should cause CPU to switch to maximal freqency.
+ This makes subsequent measurement more accurate. We need a side effect
+ to prevent the loop being deleted by compiler.
+ This should be enough to cause CPU to speed up and it is simpler than
+ running loop for constant time. This is used when user does not have root
+ access to set a constant freqency. */
+
+ int k;
+ for (k = 0; k < 10000000; k++)
+ dontoptimize += 23 * dontoptimize + 2;
+}
+
#define TIMESPEC_AFTER(a, b) \
(((a).tv_sec == (b).tv_sec) ? \
((a).tv_nsec > (b).tv_nsec) : \
@@ -32,6 +47,8 @@ main (int argc, char **argv)
unsigned long i, k;
struct timespec start, end, runtime;
+ startup();
+
memset (&runtime, 0, sizeof (runtime));
memset (&start, 0, sizeof (start));
memset (&end, 0, sizeof (end));