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Re: gettimeofday() goes backwards on FreeBSD 4.9

From: "Nigel J(dot) Andrews" <nandrews(at)investsystems(dot)co(dot)uk>
To: Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us>
Cc: Darcy Buskermolen <darcy(at)wavefire(dot)com>,"Marc G(dot) Fournier" <scrappy(at)postgresql(dot)org>,pgsql-hackers(at)postgresql(dot)org
Subject: Re: gettimeofday() goes backwards on FreeBSD 4.9
Date: 2003-11-29 01:13:28
Message-ID: Pine.LNX.4.21.0311290109470.4317-100000@ponder.fairway2k.co.uk (view raw or flat)
Thread:
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On Fri, 28 Nov 2003, Tom Lane wrote:

> "Nigel J. Andrews" <nandrews(at)investsystems(dot)co(dot)uk> writes:
> > On Fri, 28 Nov 2003, Tom Lane wrote:
> >> "Nigel J. Andrews" <nandrews(at)investsystems(dot)co(dot)uk> writes:
> > On an Intel Linux 2.4.18 I get them quite often, 25 in 1'45", but they
> > are all just a microsecond.
> >> 
> >> What do you mean by "just a microsecond"?
> 
> > I mean it's always a "out of order tv_usec..." line and the difference is
> > 1us. That is a.out gives:
> 
> > out of order tv_usec: 1070065862 374978, prev 1070065862 374979
> > out of order tv_usec: 1070065867 814300, prev 1070065867 814301
> 
> Fascinating.  I'd call that a bug too, but evidently one with a
> different mechanism than the BSD issue we are chasing.
> 
> FWIW, I have not seen any failures in a fair amount of runtime on
> a 2.4.18 (Red Hat 8.0) kernel here, running on a Dell P4.  What is
> the hardware platform you're using?

Ah, I have made a mistake. It's only a 2.2.18 kernal. Dual SMP P-III, perhaps
that's the issue there.

And on the FreeBSD system I've got this: 

$ time ./a.out 2>&1 | tee a.txt
out of order tv_sec: 1070066197 273140, prev 1070066195 721010
out of order tv_usec: 1070066197 273140, prev 1070066195 721010
out of order tv_sec: 1070067322 116061, prev 1070067320 440490
out of order tv_usec: 1070067322 116061, prev 1070067320 440490
out of order tv_sec: 1070067833 514969, prev 1070067831 755019
out of order tv_usec: 1070067833 514969, prev 1070067831 755019
^C

real    38m53.026s
user    6m13.953s
sys     32m6.589s

So not very often there.


--
Nigel



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Next:From: Marc G. FournierDate: 2003-11-29 01:19:00
Subject: Re: gettimeofday() goes backwards on FreeBSD 4.9
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