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>
index | next in thread | raw e-mail
>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
To Unsubscribe: send mail to majordomo@FreeBSD.org
with "unsubscribe freebsd-smp" in the body of the message
home |
help
Want to link to this message? Use this
URL: <https://mail-archive.FreeBSD.org/cgi/mid.cgi?199804051043.UAA00537>