Date: Sat, 29 Nov 2003 00:56:21 -0500 From: Mathew Kanner <mat@cnd.mcgill.ca> To: "Marc G. Fournier" <scrappy@hub.org> Cc: freebsd-current@freebsd.org Subject: Re: Time jumping on both 4.x and 5.x ... Message-ID: <20031129055621.GC26657@cnd.mcgill.ca> In-Reply-To: <20031128212342.G99096@ganymede.hub.org> References: <20031128212342.G99096@ganymede.hub.org>
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On Nov 28, Marc G. Fournier wrote: > > In trying to isolate an issue where the PostgreSQL 'explain analyze' is > showing "odd results" (namely, negative time estimates on queries), Tom > Lane wrote a quick C program to test gettimeofday() (program attached) ... > the results on a 4.9-PRERELEASE kernel of Sep 20 14:16:48 ADT 2003 shows: > > neptune# time ./timetest > out of order tv_sec: 1070068479 99040, prev 1070069174 725235 > out of order tv_usec: 1070068479 99040, prev 1070069174 725235 > out of order tv_sec: 1070069175 19687, prev 1070068479 99040 > out of order tv_usec: 1070069175 19687, prev 1070068479 99040 > out of order tv_sec: 1070068499 99377, prev 1070069194 625573 > out of order tv_usec: 1070068499 99377, prev 1070069194 625573 > out of order tv_sec: 1070069194 808542, prev 1070068499 99377 > ^C1.171u 23.461s 0:24.68 99.7% 5+169k 1+0io 0pf+0w > > One person on the list has tried the same script on a 5.2 kernel, and > reports seeing similar results, but after a longer period of time (~30min) > ... > > In most (all?) cases, the offset appears to be ~+/-695 secs ... Linux ppl > on the list, running the same problem, seem to be able to reproduce the > issue, except they are only finding differences of 1 microsecond, and then > only on older kernels (2.2.x, apparently) ... those running newer Linux > kernels are reporting a clean run ... FreeBSD 5.2 (up, no acpia): I get the errors only when I force heavy load and swapping. - kern.timecounter.hardware: TSC - FreeBSD tube.xx.xx5.2-BETA FreeBSD 5.2-BETA #6: Fri Nov 28 14:20:25 EST 2003 xx@xx i386 FreeBSD 4.8 (up): Didn't see the error on a nominally loaded server, I tested for about ten minutes. - kern.timecounter.hardware: i8254 - FreeBSD yy.yy.yy.yy4.8-STABLE FreeBSD 4.8-STABLE #0: Wed Jul 30 13:51:04 EDT 2003 xx@xx i386 --Mat -- sig machine boken
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