Date: Sun, 5 Apr 1998 20:43:14 +1000 From: Bruce Evans <bde@zeta.org.au> To: bde@zeta.org.au, peter@netplex.com.au Cc: phk@FreeBSD.ORG, smp@FreeBSD.ORG Subject: Re: more SMP stuff Message-ID: <199804051043.UAA00537@godzilla.zeta.org.au>
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>I was using your diff to nanosleep, but a 1 second sleep started taking
>724 seconds.... Perhaps it was the nanotime() twiddle I was trying..
Hmm.
I found the bug in microtime():
(1) the dummy timecounter has a frequency of only 10^5 Hz, but it runs
much faster than that so we get too-large delta counts.
(2) scale_micro = 10^9 * 2^32 / 10^5 / 10^3 doesn't fit in 32 bits, so
the too-large delta counts are multipled by a garbage scale factor.
microtime loops up to about 2^31 / 10^6 = 2000 times to reduce the
garbage.
nanotime() probably has the same bug, with a maximum loop count of
about 2^63 / 10^9 = 9 * 10^9, but I haven't seen this yet. If the
garbage is random, then delta is < 0 half the time, and the loop
terminates early for the wrong reason.
Bruce
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