Date: Sun, 21 Sep 2014 07:56:01 -0600 From: Ian Lepore <ian@FreeBSD.org> To: Maxim V FIlimonov <che@bein.link> Cc: freebsd-arm <freebsd-arm@freebsd.org> Subject: Re: FreeBSD-11.0-CURRENT on ARM: performance and load average Message-ID: <1411307761.66615.166.camel@revolution.hippie.lan> In-Reply-To: <16223180.9Q4Ic3raYi@quad> References: <7351653.A2UeEk9AA3@quad> <1989123.lKm0QJoZES@quad> <1411256769.66615.155.camel@revolution.hippie.lan> <16223180.9Q4Ic3raYi@quad>
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On Sun, 2014-09-21 at 13:06 +0400, Maxim V FIlimonov wrote: > On Saturday 20 September 2014 17:46:09 Ian Lepore wrote: > > > > 60 times as fast doesn't make much sense for changing a divisor to 16. > > > > Without that patch, what is the output of > > > > sysctl kern.eventtimer > > sysctl kern.timecounter > > Here it is: > root@cubie:~ # sysctl kern.eventtimer > kern.eventtimer.et.a10_timer Eventtimer.flags: 3 > kern.eventtimer.et.a10_timer Eventtimer.frequency: 24000000 > kern.eventtimer.et.a10_timer Eventtimer.quality: 1000 > kern.eventtimer.choice: a10_timer Eventtimer(1000) > kern.eventtimer.singlemul: 4 > kern.eventtimer.idletick: 0 > kern.eventtimer.timer: a10_timer Eventtimer > kern.eventtimer.periodic: 1 > root@cubie:~ # sysctl kern.timecounter > kern.timecounter.tc.a10_timer timer0.mask: 4294967295 > kern.timecounter.tc.a10_timer timer0.counter: 4271639596 > kern.timecounter.tc.a10_timer timer0.frequency: 24000000 > kern.timecounter.tc.a10_timer timer0.quality: 1000 > kern.timecounter.stepwarnings: 0 > kern.timecounter.alloweddeviation: 5 > kern.timecounter.hardware: a10_timer timer0 > kern.timecounter.choice: a10_timer timer0(1000) dummy(-1000000) > kern.timecounter.tick: 1 > kern.timecounter.fast_gettime: 1 > > > > > > If you repeatedly do "ntpdate -q <some server>" every 15 seconds for a > > couple minutes, does the offset stay pretty much the same? (like no big > > changes in the first two decimal places) Don't use a server like > > pool.ntp.org where you might get a different server every time, instead > > do "host pool.ntp.org" and pick one of the IPs and use it every time. > > > > root@cubie:~ # ntpdate time.nist.gov > 21 Sep 13:04:55 ntpdate[2236]: adjust time server 24.56.178.140 offset > -0.117727 sec > root@cubie:~ # ntpdate time.nist.gov > 21 Sep 13:04:57 ntpdate[2237]: adjust time server 24.56.178.140 offset > -0.117018 sec > root@cubie:~ # ntpdate time.nist.gov > 21 Sep 13:05:00 ntpdate[2238]: adjust time server 24.56.178.140 offset > -0.116026 sec > root@cubie:~ # ntpdate time.nist.gov > 21 Sep 13:05:08 ntpdate[2241]: adjust time server 24.56.178.140 offset > -0.111525 sec > root@cubie:~ # ntpdate time.nist.gov > 21 Sep 13:05:26 ntpdate[2242]: adjust time server 24.56.178.140 offset > -0.103121 sec > root@cubie:~ # ntpdate time.nist.gov > 21 Sep 13:05:34 ntpdate[2243]: adjust time server 24.56.178.140 offset > -0.099055 sec > > So as you could notice, the offset doesn't change much. No, quite to the contrary, the time is changing rapidly -- it moved about 19 milliseconds in 39 seconds, or roughly a millisecond every two seconds. That's an error rate of 500 parts per million, which is huge. However, it's not off by a factor of 16, so that's a bit confusing. BTW, time.nist.gov is not one server, it's a pool just like pool.ntp.org (we run one of the time.nist.gov server installations out of our building at $work). I think it probably worked for you because of some sort of dns caching effect, because you clearly kept getting the same server each time. -- Ian
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