On Wed, Feb 19, 2014 at 02:58:40PM +0000, Ledda William EXT wrote: > > I might do it one day, but so far I haven't had a really compelling reason > > to do so. Probably using the Linux system clock (and phc2sys) will be good > > enough > > most of the time. It would be interesting to find out whether that is true > > for your own application. > > Richard, > Think about this "simple" but very interesting problem. System time is not > monotonic (assuming it is in UTC), PTP time yes (assuming it is TAI). In a > real time control system you could have the need to make a "wait_until" or to > execute some functions in a very well-defined time in spite of any clock > adjustment made to recover some UTC leap second event. This could be a valid > reason to implement these features on a PHC?
Well, now that we have CLOCK_TAI in Linux, that takes of the leap second issue. I agree that it would be nice to have the PHC timers, but considering the scheduling latency on typical Linux systems (even RT), I do think using the system CLOCK_REALTIME or CLOCK_TAI will be good enough. In fact, timers built off of PHC devices which are PCIe cards will probably have *worse* latency than using system timers. I would expect that only register based SoC devices (like the gianfar) would bring any benefit at all. Thanks, Richard ------------------------------------------------------------------------------ Managing the Performance of Cloud-Based Applications Take advantage of what the Cloud has to offer - Avoid Common Pitfalls. Read the Whitepaper. http://pubads.g.doubleclick.net/gampad/clk?id=121054471&iu=/4140/ostg.clktrk _______________________________________________ Linuxptp-users mailing list Linuxptp-users@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/linuxptp-users
