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Date: Tue, 1 Nov 2005 23:42:23 +0100
From: Viktor Vasilev <viktor.vasilev@stud.tu-darmstadt.de>
To: freebsd-hackers@freebsd.org
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Subject: select(2) timeout precision
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Hello fellow hackers,

I'm writing a piece of code, that basically does the following in a
thread:

  tick.tv_sec = 0;
  tick.tv_usec = 10000;
  gettimeofday(&t1, NULL);
  select(0, NULL, NULL, NULL, &tick);
  gettimeofday(&t2, NULL);

With FreeBSD 5.4-RELEASE I almost constantly get ~20000 microseconds
delta. That is with 100HZ kernel on PIII 500MHz or Sempron 64 2800+
running in i386 mode. It also doesn't matter if I use usleep or
select.  I've tested the code on linux with 2.6.11 kernel and there I
not only get the 10000 us sleep, but I can also set it to 5000 us and
it still runs very accurately.

So my question is, is this a FreeBSD limitation of some kind, and is
there a way to circumvent it?


Best regard,
Viktor
-- 
I think and think for months and years. Ninety nine times, the
conclusion is false. The hundredth time I am right.
                               -- Albert Einstein