From mboxrd@z Thu Jan 1 00:00:00 1970 X-Spam-Checker-Version: SpamAssassin 3.4.4 (2020-01-24) on polar.synack.me X-Spam-Level: X-Spam-Status: No, score=-1.3 required=5.0 tests=BAYES_00,INVALID_MSGID autolearn=no autolearn_force=no version=3.4.4 X-Google-Language: ENGLISH,ASCII-7-bit X-Google-Thread: 103376,b3c24209310418d0,start X-Google-Attributes: gid103376,public X-Google-Thread: fee84,b3c24209310418d0,start X-Google-Attributes: gidfee84,public X-Google-Thread: 1164f8,b3c24209310418d0,start X-Google-Attributes: gid1164f8,public From: dccoote@werple.mira.net.au (David Coote) Subject: Timing Ada programs using the DEC UNIX microtimer kernel option Date: 1998/04/25 Message-ID: <6hsab5$rh1$1@eplet.mira.net.au>#1/1 X-Deja-AN: 347539924 Content-Type: Text/Plain; charset=US-ASCII Organization: werple public-access Internet Mime-Version: 1.0 Newsgroups: comp.unix.osf.osf1,comp.sys.dec,comp.lang.ada Date: 1998-04-25T00:00:00+00:00 List-Id: I got all excited when I found out about the microtimer kernel option. Timing measurements we did with this option installed did seem to indicate improved resolution. Interestingly enough, the measured overhead of various POSIX timing calls seemed to improve. (Judging from how long the call took using other timing probes.) But I'm not sure how this kernel option works. DEC USA support and what documentation exists tells me that you have a tick of 1024Hz on an AS500 and 1200Hz on an AS4100. With the microtimer kernel option installed (quoting from a DEC support email) "As for micro-timer resolution - the clock resolution remains the same - 1/1024; however, any call to clock_gettime(3) is guaranteed to be monotonically increasing with a granularity of 1 microsecond. (i.e. the clock is still ticking at 1/1024, but clock_gettime(3) calls return values that are unique and APPEAR [DEC's emphasis] to have 1 microsecond resolution. This is useful for critical timestamping.)" Well, how do they do this monotonic increase? If the appropriate parts of the kernel are getting tickled every 1024Hz, how is the kernel returning finer resolution between ticks? Anyone know anything about this? David