This is a patch from John, written a few months back. I have fixed up a
few cosmetic whitespace bits, and have refreshed it so it should apply
cleanly to LTP today.
Comments originally by John Stultz:
So I've been trying to go through and review our test cases to make sure
we're getting sane data and the tests are really testing what we want.
Looking at gtod_latency and gtod_infinite, I was always struck that
gtod_infinite always came up with much larger latencies while
gtod_latency usually seemed to miss them.
Main issues:
1) gtod_latency was not running for long enough, I've upped the
iterations by 10x to make sure we get more solid results.
2) gtod_latency was doing too much computation between gtod calls. This
means it could miss latencies that occur while it was running. I
reworked the data collection loop so the un-measured window is smaller.
3) gtod_infinite was accidentally measuring its own computation in its
delay, inflating its values. I cut that logic out.
4) both gtod_latency and gtod_infinite were not running mlocked. this
caused background SCHED_OTHER disk access to inject delays, making the
results less reliable.
Those four issues have been fixed, and I also converted gtod_latency to
use clock_gettime() just to be consistent and to give slightly better
resolution.
-john
Signed-off-by: John Stultz <[EMAIL PROTECTED]>
Acked-by: Darren Hart <[EMAIL PROTECTED]>
Acked-by: Will Schmidt <[EMAIL PROTECTED]>
---
diff -Naur ltp.orig/testcases/realtime/func/gtod_latency/gtod_infinite.c
ltp/testcases/realtime/func/gtod_latency/gtod_infinite.c
--- ltp.orig/testcases/realtime/func/gtod_latency/gtod_infinite.c
2008-08-18 13:15:21.000000000 -0500
+++ ltp/testcases/realtime/func/gtod_latency/gtod_infinite.c 2008-08-18
12:22:23.000000000 -0500
@@ -53,6 +53,7 @@
#include <sched.h>
#include <librttest.h>
#include <libjvmsim.h>
+#include <sys/mman.h>
/* #define CLOCK_TO_USE CLOCK_MONOTONIC */
#define CLOCK_TO_USE CLOCK_REALTIME
@@ -66,9 +67,9 @@
void usage(void)
{
rt_help();
- printf("gtod_infinite specific options:\n");
- printf(" -j enable jvmsim\n");
- printf(" -wWINDOW iterations in max value window (default
inf)\n");
+ printf("gtod_infinite specific options:\n");
+ printf(" -j enable jvmsim\n");
+ printf(" -wWINDOW iterations in max value window (default
inf)\n");
}
int parse_args(int c, char *v)
@@ -121,9 +122,11 @@
printf("jvmsim disabled\n");
}
+ mlockall(MCL_CURRENT|MCL_FUTURE);
+
if (max_window > 0) {
- printf("%d iterations in max calculation window\n",
- max_window);
+ printf("%d iterations in max calculation window\n",
+ max_window);
}
param.sched_priority = sched_get_priority_min(SCHED_FIFO) + 80;
@@ -141,6 +144,7 @@
wi = 0;
while(1) {
+ rc = clock_gettime(CLOCK_TO_USE, &p_ts);
rc = clock_gettime(CLOCK_TO_USE, &ts);
if (rc) {
perror("clock_gettime");
@@ -153,11 +157,11 @@
diff_time = e_time - s_time;
if (max_window > 0 ||
- ((diff_time > max_time) ||
+ ((diff_time > max_time) ||
(diff_time > REPORT_MIN))) {
if (diff_time > max_time)
max_time = diff_time;
-
+
if (max_window == 0 || ++wi == max_window) {
tt = (time_t)ts.tv_sec;
printf("Task delayed for %lld nsec!!! %s",
@@ -170,13 +174,6 @@
}
}
- rc = clock_gettime(CLOCK_TO_USE, &p_ts);
- if (rc) {
- perror("clock_gettime");
- exit(1);
- }
- } else {
- p_ts = ts;
}
}
return 0;
diff -Naur ltp.orig/testcases/realtime/func/gtod_latency/gtod_latency.c
ltp/testcases/realtime/func/gtod_latency/gtod_latency.c
--- ltp.orig/testcases/realtime/func/gtod_latency/gtod_latency.c
2008-08-18 13:15:21.000000000 -0500
+++ ltp/testcases/realtime/func/gtod_latency/gtod_latency.c 2008-08-18
12:22:10.000000000 -0500
@@ -54,8 +54,9 @@
#include <limits.h>
#include <libstats.h>
#include <librttest.h>
+#include <sys/mman.h>
-#define ITERATIONS 1000000
+#define ITERATIONS 10000000
#define HIST_BUCKETS 20
#define SCATTER_FILENAME 0
@@ -202,19 +203,20 @@
}
-/* return difference in microseconds */
-unsigned long long tv_minus(struct timeval *tv_start, struct timeval *tv_end)
+long long timespec_subtract(struct timespec * a, struct timespec *b)
{
- unsigned long long usecs;
- usecs = (tv_end->tv_sec - tv_start->tv_sec) * 1000000;
- usecs += tv_end->tv_usec - tv_start->tv_usec;
- return usecs;
+ long long ns;
+ ns = (b->tv_sec - a->tv_sec) * 1000000000LL;
+ ns += (b->tv_nsec - a->tv_nsec);
+ return ns;
}
+struct timespec start_data[ITERATIONS];
+struct timespec stop_data[ITERATIONS];
+
int main(int argc, char *argv[])
{
int i, err;
- struct timeval tv_a, tv_b;
unsigned long long delta;
unsigned long long max, min;
struct sched_param param;
@@ -227,6 +229,8 @@
stats_quantiles_init(&quantiles, (int)log10(ITERATIONS));
setup();
+ mlockall(MCL_CURRENT|MCL_FUTURE);
+
if (stats_cmdline(argc, argv) < 0) {
printf("usage: %s help\n", argv[0]);
exit(1);
@@ -242,7 +246,7 @@
fprintf(stderr, "This program runs with a scheduling
policy of SCHED_FIFO at priority %d\n", param.sched_priority);
fprintf(stderr, "You don't have the necessary
privileges to create such a real-time process.\n");
} else {
- fprintf(stderr, "Failed to set scheduler, errno %d\n",
errno);
+ fprintf(stderr, "Failed to set scheduler, errno %d\n",
errno);
}
exit(1);
}
@@ -259,9 +263,11 @@
latency_trace_start();
}
for (i = 0; i < ITERATIONS; i++) {
- gettimeofday(&tv_a, NULL);
- gettimeofday(&tv_b, NULL);
- delta = tv_minus(&tv_a, &tv_b);
+ clock_gettime(CLOCK_MONOTONIC,&start_data[i]);
+ clock_gettime(CLOCK_MONOTONIC,&stop_data[i]);
+ }
+ for (i = 0; i < ITERATIONS; i++) {
+ delta = timespec_subtract(&start_data[i], &stop_data[i]);
dat.records[i].x = i;
dat.records[i].y = delta;
if (i == 0 || delta < min) min = delta;
@@ -273,7 +279,7 @@
latency_trace_stop();
if (i != ITERATIONS) {
printf("Latency threshold (%lluus) exceeded at
iteration %d\n",
- latency_threshold, i);
+ latency_threshold, i);
latency_trace_print();
stats_container_resize(&dat, i + 1);
}
@@ -281,19 +287,18 @@
stats_hist(&hist, &dat);
stats_container_save(filenames[SCATTER_FILENAME], titles[SCATTER_TITLE],
- labels[SCATTER_LABELX], labels[SCATTER_LABELY],
&dat, "points");
+ labels[SCATTER_LABELX], labels[SCATTER_LABELY],
&dat, "points");
stats_container_save(filenames[HIST_FILENAME], titles[HIST_TITLE],
- labels[HIST_LABELX], labels[HIST_LABELY], &hist,
"steps");
+ labels[HIST_LABELX], labels[HIST_LABELY],
&hist, "steps");
/* report on deltas */
- printf("Min: %llu us\n", min);
- printf("Max: %llu us\n", max);
- printf("Avg: %.4f us\n", stats_avg(&dat));
- printf("StdDev: %.4f us\n", stats_stddev(&dat));
+ printf("Min: %llu ns\n", min);
+ printf("Max: %llu ns\n", max);
+ printf("Avg: %.4f ns\n", stats_avg(&dat));
+ printf("StdDev: %.4f ns\n", stats_stddev(&dat));
printf("Quantiles:\n");
stats_quantiles_calc(&dat, &quantiles);
stats_quantiles_print(&quantiles);
-
return 0;
}
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