6 Replies Latest reply on Jun 5, 2009 7:59 AM by clebert.suconic

    nanoSleep

    clebert.suconic
    clebert.suconic Jun 4, 2009 1:29 PM

      I'm writing a native call to nanoSleep.

      As we have talked over IRC, I'm measuring the precision, and the weight of JNI calls.

      I have made a bunch of tests:

      My conclusion is that it is close enough for 20K.


      Follows a table:



      Time IntervalNumber Of LoopsTime Taken


      01,000,00017 milliseconds


      1000 nanosecond1,000,0003856 milliseconds


      20 K nanosecond1,000,00023312 milliseconds




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        • 1. Re: nanoSleep
          timfox
          timfox Jun 4, 2009 2:00 PM (in response to clebert.suconic)

          Ok, so how about we plump for 15K nano sleep, which should give us about 20K actual nano seconds, i.e. 20 microseconds...

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          • 2. Re: nanoSleep
            clebert.suconic
            clebert.suconic Jun 4, 2009 6:35 PM (in response to clebert.suconic)

            We will need to go back to System.nanoTime().

            there are some kernel versions that don't play well with timing. nanosleep, usleep or any other native sleep has ticking problems.

            Or maybe.. we keep native-timers, and let the user decide on flush-on-sync. That would save some cpu cycles.

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            • 3. Re: nanoSleep
              clebert.suconic
              clebert.suconic Jun 4, 2009 6:36 PM (in response to clebert.suconic)

              Phillip Thurmond sent me this link:


              http://fixunix.com/unix/552033-problem-nanosleep.html

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              • 4. Re: nanoSleep
                clebert.suconic
                clebert.suconic Jun 5, 2009 1:31 AM (in response to clebert.suconic)

                The minimal resolution I have found on Rhel is 1 millisecond. No matter what you do. (No wonder Java has decided to not implement System.sleep for micro and nanosleep yet). That's a mess when you consider multiple platform even among different kernel versions.

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                • 5. Re: nanoSleep
                  timfox
                  timfox Jun 5, 2009 5:27 AM (in response to clebert.suconic)

                   

                  "clebert.suconic@jboss.com" wrote:
                  The minimal resolution I have found on Rhel is 1 millisecond. No matter what you do. (No wonder Java has decided to not implement System.sleep for micro and nanosleep yet). That's a mess when you consider multiple platform even among different kernel versions.


                  Clebert, this does not make sense.

                  Earlier in this thread you posted results that showed 1000000 nanosleeps taking in total 17, 3856 milliseconds, which is way less than 1 ms, so your statement is completely contradictory to your results.

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                  • 6. Re: nanoSleep
                    clebert.suconic
                    clebert.suconic Jun 5, 2009 7:59 AM (in response to clebert.suconic)

                    As I said... there are some kernel versions that don't play well with timing.


                    depending on the Linux version, this will play differently, and the kernel version on RHEL (our performance lab) has the bug on the kernel in place.

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