Hi! > >>>>>is even worse than that. Machine can stay is s2ram for weeks (for a > >>>>>lot more if it is desktop and you do s2ram for powersaving). Also > >>>>>temperature of CPU varies a lot between active and s2ram states. Is > >>>>>TSC good enough? > >>>>Yes, I think it is relatively precise. Per our test, system time backed > >>>>by the S3 non stop TSC only has 1 second drift after 4 days running > >>>>(with mixed running and S3 states). And before using this feature, we've > >>>>seen many time drift problems due to the RTC HW or system FW with our > >>>>platforms. > >>>Nice result ... > >>> > >>>Is that with NTP running? > >>> > >>>Without NTP, the TSC fast-calibration on bootup is not (expected to be) > >>>nearly as precise as the 1:345600 precision you've measured. > >>We also do refined calibration now on the TSC asynchronously over a > >>period of seconds at boot up that gives us much better accuracy then > >>the fast calibration. This helps provide much more consistent > >>boot-to-boot TSC frequencies. > >On android (and this is targetted at android, right?) system is going > >to suspend basically as soon as it boots. Will refined calibration > >have enough time to do its job? > I don't *think* this is a concern. The refined calibration only > takes a few seconds while the system is booting and has always > completed before userspace starts on the systems I have. Even so, I > don't believe on boot Android will trigger the autosleep code until > its userland is up and running, which takes more then a few seconds > on the devices I've seen.
Userspace has to be running, right. It should boot in 10 seconds or so. > >And... reason for all this is that RTC has one second granularity when > >accessed naively. But surely we could poll RTC X times a second, > >getting error down by factor of X? > Well, we can poll the RTC trying to get closer to the second edge, > but that's somewhat expensive, and for suspend/resume would delay > things more then whats acceptable. Well, if > Sorry. You seem to not like the merged change, but I guess I'm not > quite sure what exactly your objection is here. I'm not exactly sure what my objections are. TSC was not designed for long-term precise timekeeping. I guess it may work ok for short naps, but some people suspend their machines for longer than that. Plus I wonder how it will interfere with /etc/adjtime. Pavel -- (english) http://www.livejournal.com/~pavelmachek (cesky, pictures) http://atrey.karlin.mff.cuni.cz/~pavel/picture/horses/blog.html -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/