Miroslav, You said it exactly slam-dunk right on the head.
Timer queue facilities are tricky and can be absolutely awful to debug when something doesn't work right. I know this, as I built what might now be called a tickless kernel for the PDP11 fuzzball in 1979. It did avoid program interrupts to increment timers, which was important in those old, slow machines, but it did require considerable overhead to scan, insert and remove queue entries and worry about hash tables. If you have been with this project for many years, you know a timer queue facility was once implemented in xntpd and carried over to early ntpd. However, it was fragile, poorly implemented, impossible to maintain and eventually was ripped out. You can understand my reluctance to repeat that adventure. Over the years there have been a number of occasions where somebody dumps something on the distributution and then disappears. Ten years later I stumble over it because it has broken something, then realize it never did work properly, so I rip it out. But the real slam-dunk issue is who is going to maintain the facility if it is incorporated in ntpd? How will it affect future enhancements? Is it to be optional and enabled by defines and configure? If Linux folks think it necessary and maintain it, nobody here needs to worry. However, the Linux folks might have to worry if something in the distribution changes and the patch doesn't work any more. Dave Miroslav Lichvar wrote: > On Thu, May 15, 2008 at 06:51:24PM +0200, Jan Ceuleers wrote: > >>I came across the following page: >> >>http://www.lesswatts.org/projects/powertop/known.php >> >>which says the following on ntpd: >> >>"By default, the ntp time synchronization daemon will wake up once per >>second, and will make the kernel do work on it's behalf even more. Red >>Hat has created a patch to ntp to fix this issue and ships it in their >>rawhide and FC7 ntp packages. You can download this patch from the >>Fedora cvs server." >> >>Has anyone here looked at that patch? Does it compromise correctness of >>the algorithms? > > > A bug report for this issue is here: > https://support.ntp.org/bugs/show_bug.cgi?id=802 > > There are two different patches, the first one is just looking ahead > for the next event and it should be safe to use (at least on Linux). > The second patch implements a queue timer, it is more complex and > harder to maintain. In the Fedora CVS is maintained the first patch, > a version for the latest stable ntp release can also be found there. > _______________________________________________ questions mailing list [email protected] https://lists.ntp.org/mailman/listinfo/questions
