Hello Helge, On 2/20/20 6:24 PM, Helge Deller wrote: > Consecutive calls to clock_gettime(CLOCK_MONOTONIC) are guaranteed to > return MONOTONIC values, which means that they either return the *SAME* > time value like the last call, or a later (higher) time value. > > Due to high resolution counters like TSC on x86 most people see that the > values returned increase, but on other less common platforms it's less > likely that consecutive calls return newer values, and instead users may > unexpectely get back the SAME time value. > > I think it makes sense to document that people should not expect to see > "always-growing" time values. For example in Debian I've seen in quite > some source packages where return values of consecutive calls are > compared against each other and then the package build fails if they are > equal (e.g. ruby-hitimes, ...). > > The patch below is just for RFC. I'm open for any better wording! > > Signed-off-by: Helge Deller <deller@xxxxxx> > > diff --git a/man2/clock_getres.2 b/man2/clock_getres.2 > index 646fa37c0..89e9f6a30 100644 > --- a/man2/clock_getres.2 > +++ b/man2/clock_getres.2 > @@ -151,6 +151,10 @@ but is affected by the incremental adjustments performed by > .BR adjtime (3) > and NTP. > This clock does not count time that the system is suspended. > +All > +.B CLOCK_MONOTONIC > +variants guarantee that the time returned by consecutive calls will not go > +backwards, but they may return the identical (not-increased) time value. > .TP > .BR CLOCK_MONOTONIC_COARSE " (since Linux 2.6.32; Linux-specific)" > .\" Added in commit da15cfdae03351c689736f8d142618592e3cebc3 Thanks. I applied your patch, and then tweaked slightly, so tha the change looks as below. Cheers, Michael diff --git a/man2/clock_getres.2 b/man2/clock_getres.2 index 646fa37c0..3fb0ac61c 100644 --- a/man2/clock_getres.2 +++ b/man2/clock_getres.2 @@ -151,6 +151,11 @@ but is affected by the incremental adjustments performed by .BR adjtime (3) and NTP. This clock does not count time that the system is suspended. +All +.B CLOCK_MONOTONIC +variants guarantee that the time returned by consecutive calls will not go +backwards, but successive calls may\(emdepending on the architecture\(emreturn +identical (not-increased) time values. .TP .BR CLOCK_MONOTONIC_COARSE " (since Linux 2.6.32; Linux-specific)" .\" Added in commit da15cfdae03351c689736f8d142618592e3cebc3 -- Michael Kerrisk Linux man-pages maintainer; http://www.kernel.org/doc/man-pages/ Linux/UNIX System Programming Training: http://man7.org/training/
