Re: [LTP] [PATCH] nanosleep02

[Kelly L. <luc...@fa...>]

I agree, as I almost always get test case failures when testing this 
specific testcase.

kdl

Kelly D. Lucas
luc...@fa...



Sripathi Kodi wrote:

> Hi,
>
> Please copy me on replies as I have not subscribed to this list.
>
> I am seeing nanosleep02 testcase failure on RHEL3 machines (kernel 
> 2.4.21-32.11.EL and other RHEL3 kernels). I believe the accuracy 
> expected out of 'nanosleep' call in this testcase is too high and that 
> is the cause of the problem. I have explained the reasons and provided 
> a patch for the testcase below. Failure looks like this:
>
> nanosleep02    1  FAIL  :  Remaining sleep time 4010000 usec doesn't 
> match with the expected 3999622 usec time
> nanosleep02    1  FAIL  :  child process exited abnormally
>
> Explanation:
> ------------
> nanosleep02 testcase does the following:
> gettimeofday - before
> nanosleep. - Interrupt the sleeping process by sending SIGINT
> gettimeofday - after
>
> It then compares the time remaining returned by nanosleep with the 
> difference in time shown by the two gettimeofday calls. It expects the 
> difference to be less than 2000 microseconds.
>
> Compare this to nanosleep01 testcase. It is a simple test that lets 
> the process sleep with nanosleep and checks how long it has slept. The 
> SLOP_MS value, which is the allowed error margin, is 250 milliseconds. 
> It does all calculations and comparisons in milliseconds.
>
> Whereas nanosleep02 does all calculations in microseconds. However, 
> 'nanosleep' call is limited by the kernel timer mechanism, which can 
> afford an accuracy of 1/HZ at best. From the manpage of 'nanosleep':
> "The current implementation of nanosleep is based on the normal kernel 
> timer mechanism, which has a  resolution  of 1/HZ s (i.e, 10 ms on 
> Linux/i386 and 1ms on Linux/Alpha). Therefore, nanosleep pauses always 
> for at least the specified time, however it can take up to 10 ms 
> longer than specified until the process  becomes  runnable  again. 
> For  the same  reason, the value returned in case of a delivered 
> signal in *rem is usually rounded to the next larger multiple of 1/HZ s."
>
> So while looking at the remaining time returned by an interrupted 
> 'nanosleep' call, the error margin we should be ready to allow is 
> (1/HZ * 2), which is 20milliseconds. In fact 'nanosleep01' is quite 
> generous!
>
> The behavior shown by 'nanosleep' call is acceptable by POSIX 
> standards as well. It says 
> (http://www.opengroup.org/onlinepubs/007908799/xsh/nanosleep.html): 
> "The suspension time may be longer than requested because the argument 
> value is rounded up to an integer multiple of the sleep resolution or 
> because of the scheduling of other activity by the system. But, except 
> for the case of being interrupted by a signal, the suspension time 
> will not be less than the time specified by rqtp, as measured by the 
> system clock, CLOCK_REALTIME."
>
> So I think we should change the testcase. I am attaching a patch to 
> suggest changes for this. Please note that I have set the error margin 
> to be same as nanosleep01, which is 250milliseconds. It can be set as 
> low as 20 milliseconds, but if the system is heavily loaded, it may 
> lead to the test failing again.
>
>
> Thanks and regards,
> Sripathi.
>
> Patch:
> ------
>
> --- testcases/kernel/syscalls/nanosleep/nanosleep02.c    2005-08-02 
> 13:48:29.000000000 -0500
> +++ /home/sripathi/17215/nanosleep02.c    2005-08-02 
> 13:40:38.000000000 -0500
> @@ -101,7 +101,7 @@ void sig_handler();        /* signal catching
>   * the "rem" field would never change without the increased
>   * usec precision in the -aa tree.
>   */
> - #define USEC_PRECISION 2200  /* Originally set at 100 max but this 
> compiler bug has been around for years. */
> +#define MSEC_PRECISION 250      /* Error margin allowed in 
> milliseconds */
>
>  int
>  main(int ac, char **av)
> @@ -185,7 +185,7 @@ main(int ac, char **av)
>  void
>  do_child()
>  {
> -    unsigned long req, rem, before, after, elapsed; /* usec */
> +    unsigned long req, rem, before, after, elapsed; /* msec */
>      struct timeval otime;         /* time before child execution 
> suspended */
>      struct timeval ntime;         /* time after child resumes 
> execution */
>
> @@ -208,15 +208,15 @@ do_child()
>       * The time remaining should be equal to the
>       * Total time for sleep - time spent on sleep bfr signal
>       */
> -    req = timereq.tv_sec * 1000000 + timereq.tv_nsec / 1000;
> -    rem = timerem.tv_sec * 1000000 + timerem.tv_nsec / 1000;
> -    before = otime.tv_sec * 1000000 + otime.tv_usec;
> -    after = ntime.tv_sec * 1000000 + ntime.tv_usec;
> +    req = timereq.tv_sec * 1000 + timereq.tv_nsec / 1000000;
> +    rem = timerem.tv_sec * 1000 + timerem.tv_nsec / 1000000;
> +    before = otime.tv_sec * 1000 + otime.tv_usec/1000;
> +    after = ntime.tv_sec * 1000 + ntime.tv_usec/1000;
>      elapsed = after - before;
>
> -    if (rem - (req - elapsed) > USEC_PRECISION) {
> -        tst_resm(TFAIL, "Remaining sleep time %lu usec doesn't "
> -             "match with the expected %lu usec time",
> +    if (rem - (req - elapsed) > MSEC_PRECISION) {
> +        tst_resm(TFAIL, "Remaining sleep time %lu msec doesn't "
> +             "match with the expected %lu msec time",
>               rem, (req - elapsed));
>          exit(1);
>      }
>
>
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