Em Fri, Jul 31, 2020 at 06:46:21PM -0600, David Ahern escreveu: > On 7/31/20 12:05 PM, [email protected] wrote: > > On Fri, Jul 31, 2020 at 08:36:12AM -0700, Andi Kleen wrote: > >>> yep, we have a customer that needs to compare data from multiple servers
> >> It's also needed to correlate over different guests on the same machine. > >> This is an important use case. > > Both these cases you want to sync up CLOCK_MONOTONIC, using walltime is > > just utterly misguided. > Every userspace component logs in walltime. You can say that is > misguided, but that is the way it is. The missing piece is the ability > to correlate kernel events to userspace logs. > > What happens if the servers have (per accident or otherwise) different > > DST settings, or someone does a clock_setttime() for giggles. > Yes, someone *could* change the time. Someone *could* start ntpd or > other time server in the middle of a session. While technically such > things can happen, that is not real life in most environments (e.g., > Data center servers). ntpd (or other) is started at boot, and it is just > the little misc adjustments that happen over time. > We could add tracepoints and detect the changes and invalidate the > reference time. We could add tracepoints to track the adjustments and > update the reference time. In my experience over 9+ years using this > tool (out of tree patches) that has never been the problem. > > All you really want is a clock that runs at the same rate but is not > > subject to random jumps and user foibles. > All I want is to compare user logs to a kernel event via timestamps. Can we have both possibilities and leave the decision on which one to use in the hands of those who have a gun to shoot wherever they want, maybe in the foot? - Arnaldo
