Luigi Rizzo wrote: > On Tue, Oct 07, 2003 at 06:17:04PM -0400, [EMAIL PROTECTED] wrote: > > We did some intensive profiling of our application. It does not seem like > > we are depending on clock ticks for any calculations. > > > > On the other hand we notice that our slow iterations happen almost at the > > same instant as "microuptime went backward" messages in the system log. We > > if this is the case, probably your code at some point computes a > time difference which turns out negative (or if it is unsigned, it > becomes very very large) upon those events, thus causing some loop > to explode. > It should be easy to check if this is the case, and just ignore > those outliers rather than trying to figure out why the clock > goes backward. I used to see the same "microuptime went backwards" > msg on some of my 400MHz boxes, even without NTP enabled. > Maybe a buggy timer, not sure which timecounter was used on that > box (i read some time ago that the cpu on the soekris4801 has a > weird TSC implementation where the upper 32 bits change when the > lower 32 bits are 0xfffffffd, who knows what other bugs might be > in other hardware...)
FWIW: Internally, MacOS X supports "monotime", which is a monotonically increasing time counter, guaranteed to not go backwards. That avoids problems exactly like what you are describing. FreeBSD should consider supporting a "monotime". -- Terry _______________________________________________ [EMAIL PROTECTED] mailing list http://lists.freebsd.org/mailman/listinfo/freebsd-hackers To unsubscribe, send any mail to "[EMAIL PROTECTED]"
