On 2/23/20 10:26 PM, Helge Deller wrote: > 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! Thanks for checking! Cheers, Michael -- Michael Kerrisk Linux man-pages maintainer; http://www.kernel.org/doc/man-pages/ Linux/UNIX System Programming Training: http://man7.org/training/
