On Feb 22, 2011, at 1:22 AM, Jerome Flesch wrote: >> A scheduler quantum of 10ms (or HZ=100) is a common granularity; probably >> some other process got the CPU and your timer process didn't run until the >> next or some later scheduler tick. If you are maxing out the available CPU >> by running many "openssl speed" tasks, then this behavior is more-or-less >> expected. >> > > We did most of our tests with kern.hz=1000 (the default FreeBSD value as far > as I know) and we also tried with kern.hz=2000 and kern.hz=10000. It didn't > change a thing.
For a long time kern.hz=100 was the default; more recent versions have switched to kern.hz=1000, which is beneficial for minimizing latency for things like ipfw/dummynet processing, but also involve greater scheduler overhead. kern.hz=10000 is likely to reduce performance and may have odd effects upon certain kernel timers. > Also, we are talking about a process not being scheduled for more than 100ms > with only 1 instance of openssl on the same CPU core. Even with a scheduler > quantum of 10ms, I find that worrying :/ It depends on what else the machine is doing. Gathering some data via acct/sa might be informative, as you might be running some other tasks via cron or whatever which your testing isn't expecting. > We expected both processes (the test program and openssl) to have each half > the CPU time and being scheduled quite often (at least once each 10ms). > According to the output of our test program, it works fine for most of the > calls to clock_gettime(), but from time to time (about 1 loop in 200000 on my > computer), we have a latency pike (>= 100ms). > > Thing is, these pikes wouldn't worry us much if they wouldn't last longer > than 1s, but they do on some occasions. Also, are you sure that you don't have ntpdate or ntpd or something else adjusting your system clock underneath you...? Regards, -- -Chuck _______________________________________________ freebsd-current@freebsd.org mailing list http://lists.freebsd.org/mailman/listinfo/freebsd-current To unsubscribe, send any mail to "freebsd-current-unsubscr...@freebsd.org"
