On Nov 18, 2011, at 12:01 PM, Scott Wood wrote: > On Fri, Nov 18, 2011 at 08:35:02AM -0600, Kumar Gala wrote: >> >> On Nov 16, 2011, at 12:42 PM, Scott Wood wrote: >> >>> On 11/16/2011 03:55 AM, Zhao Chenhui wrote: >>>> From: Li Yang <le...@freescale.com> >>>> >>>> The timebase sync is not only necessary when using KEXEC. It should also >>>> be used by normal boot up and cpu hotplug. Remove the ifdef added by >>>> the KEXEC patch. >>> >>> Again, no it should not be used by normal boot up (whether KEXEC support >>> is enabled or not). We should only do timebase sync when we actually >>> need to (when we've actually just reset a core), and we should do it the >>> way U-Boot does rather than with smp-tbsync.c. >> >> >> How can we do u-boot bases timebase sync after the system us up and >> running? For example would we losing some ticks of time in the case >> that one core is up and we bring a second core online? > > Yes, we'll lose a small handful of ticks relative to wall clock time -- > but it'll be the same loss on all cores. It's better than possibly > having the timebase be imperfectly synchronized, and should complete more > quickly.
Hmm, I wondering how many ticks it really is. > This is only during intrusive events such as kexec or deep sleep (we only > need to reset the core for jog on mpc8536 which has only one core). > During deep sleep all cores' timebases will be stopped. Kexec is > resetting the kernel; it's not going to care what the old timebase was, > and should resync from RTC. > > Even if we end up using this for some future power management mode where > we take down some CPUs to the point their timebase stops, but never take > down others, the time loss should be negligible (for comparison, what's > the error tolerance on the crystal frequency?) and acceptable for what is > still a fairly intrusive and rare event. I'm also concerned about how this ends up working for p4080 when we have to sync up to 8 cores or more in the future. - k _______________________________________________ Linuxppc-dev mailing list Linuxppc-dev@lists.ozlabs.org https://lists.ozlabs.org/listinfo/linuxppc-dev
