On 23.02.20 22:09, Michael Kerrisk (man-pages) wrote: > 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. Looks good. Thanks! Helge > 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 > > >
