Re: settimeofday function taking 24 - 30 minutes to complete

2006/12/19, Garrett Cooper <youshi10_at_u.washington.edu>:
> Scot Hetzel wrote:
> > While working on implementing the settimeofday function in the
> > linuxolator, I was using the LTP testcase settimeofday01 to test it.
> > Running this test caused the system to hang for 24-30 minutes.
> >
> > I then decided to rewrite the testcase so that it would run on
> > FreeBSD, and it also hung the system for 24-30 minutes.  What the
> > settimeofday01 test was doing is to set the time to a known value (100
> > sec, 100 usec) and then use gettimeofday to retrieve the current time.
> > It then compared the returned value to check if it was within +/- 500
> > msec.
> >
> > I have since reduced the testcode down to the following testcase that
> > is causing the hang.
> >
> > Any ideals as to what could be causing this hang?
> >
> > Scot
> >
> > #include <sys/time.h>
> > #include <errno.h>
> > #include <unistd.h>
> >
> > #define VAL_SEC         100
> > #define VAL_MSEC        100
> >
> > int main(int argc, char **argv)
> > {
> >        struct timeval tp, tp1, save_tv;
> >        long return_test, errno_test;
> >        suseconds_t delta;
> >
> > #define TEST(SCALL) \
> >        do { \
> >                errno = 0; \
> >                return_test = SCALL; \
> >                errno_test = errno; \
> >        } while (0)
> >
> >        /* Save the current time values */
> >        if ((gettimeofday(&save_tv, (struct timezone *)&tp1)) == -1) {
> >                printf("BROK: gettimeofday failed. errno=%d\n", errno);
> >                exit(1);
> >        } else {
> >                printf("INFO: Saved current time\n");
> >        }
> >
> >        tp.tv_sec  =  VAL_SEC;
> >        tp.tv_usec  =  VAL_MSEC;
> >
> >        /* Hang occurs here */
> >        TEST(settimeofday(&tp, NULL));
> >        if (return_test == -1) {
> >                printf("FAIL: Error Setting Time, errno=%d\n",
> > errno_test);
> >        } else {
> >                printf("INFO: settimeofday completed sucessfully\n");
> >        }
> >
> >        /* restore the original time values. */
> >        if ((settimeofday(&save_tv, NULL)) == -1) {
> >                printf("WARN: FATAL COULD NOT RESET THE CLOCK\n");
> >                printf("FAIL: Error Setting Time, errno=%d (%d, %d)\n",
> >                         errno, tp.tv_sec, tp.tv_usec);
> >        } else {
> >                printf("INFO: Reset time to original value\n");
> >        }
> >
> >        return(0);
> > }
> >
>     Not sure about why it takes so long to complete, but it seems as if
> the system is 'hanging' because it probably is using up all of your CPU
> resources in the while loop under your TEST macro. Maybe the near 100%
> CPU usage is effecting kernel operations as well, i.e. slowing it down
> to stone age speeds? sleep(3)/nanosleep(2) to the rescue?

The while loop in the TEST macro is a do { /* ... */ } while (0); so
it should only execute once.

--Devon

> -Garrett
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