[PATCH] do_gettimeofday() fails to compensate for lost ticks

Khalid Aziz
2003-09-24T17:21:19Z

do_gettimeofday() needs to account for lost ticks before returning
current time and it fails to do that. do_gettimeofday() on other
architectures compensate for lost ticks correctly. Due to this bug, if
you repeatedly do clock_settime() immediately followed by clock_gettime()
and compare the time returned by clock_gettime() to the time set by
clock_settime(), you will eventually see clock going backwards. I am
attaching a test program from POSIX testsuite at the end that exposes
this bug. Run this test in a continuous loop that stops when test fails.

Following patch should address this issue.

--
Khalid

===========
--- linux-2.4.22/arch/ia64/kernel/time.c Mon Aug 25 05:44:39 2003
+++ linux-2.4.22-clock_fix/arch/ia64/kernel/time.c Wed Sep 24 11:14:54 2003
@@ -132,6 +132,7 @@

sec = xtime.tv_sec;
usec += xtime.tv_usec;
+ usec += (jiffies - wall_jiffies) * (1000000 / HZ);
}
read_unlock_irqrestore(&xtime_lock, flags);

========= Test program =========
/*
* Copyright (c) 2002, Intel Corporation. All rights reserved.
* Created by: julie.n.fleischer REMOVE-THIS AT intel DOT com
* This file is licensed under the GPL license. For the full content
* of this license, see the COPYING file at the top level of this
* source tree.

* Test that clock_settime() sets clock_id to tp.
*
* The clock_id chosen for this test is CLOCK_REALTIME.
* The date chosen is Nov 12, 2002 ~11:13am (date when test was first
* written).
*/
#include <stdio.h>
#include <time.h>
/*#include "posixtest.h"
#include "helpers.h"*/

#define TESTTIME 1037128358
#define ACCEPTABLEDELTA 1
#define PTS_UNRESOLVED 2
#define PTS_PASS 0
#define PTS_FAIL 1

int getBeforeTime(struct timespec *tpget)
{
if (clock_gettime(CLOCK_REALTIME, tpget) != 0) {
perror("clock_gettime() did not return success\n");
perror("clock may not be reset properly\n");
return PTS_UNRESOLVED;
}
return PTS_PASS;
}

int setBackTime(struct timespec tpset)
{
if (clock_settime(CLOCK_REALTIME, &tpset) != 0) {
perror("clock_settime() did not return success\n");
perror("clock may not be reset properly\n");
return PTS_UNRESOLVED;
}
return PTS_PASS;
}

int main(int argc, char *argv[])
{
struct timespec tpset, tpget, tpreset;
int delta;

getBeforeTime(&tpreset);

tpset.tv_sec = TESTTIME;
tpset.tv_nsec = 0;
if (clock_settime(CLOCK_REALTIME, &tpset) = 0) {
if (clock_gettime(CLOCK_REALTIME, &tpget) = -1) {
perror("Error in clock_gettime()");
return 2;
}
delta = tpget.tv_sec-tpset.tv_sec;
if ( (delta <= ACCEPTABLEDELTA) && (delta >= 0) ) {
printf("Test PASSED\n");
setBackTime(tpreset);
return 0;
} else {
printf("delta = %d, tpget=%d,%d, tpset=%d,%d\n", delta, tpget.tv_sec, tpget.tv_nsec, tpset.tv_sec, tpset.tv_nsec);
printf("clock does not appear to be set\n");
setBackTime(tpreset);
return 1;
}
} else {
printf("clock_settime() failed\n");
return 2;
}

printf("This code should not be executed.\n");
return 2;
}