Messages in this thread | | | Date | Tue, 07 May 2013 14:39:35 -0700 | From | John Stultz <> | Subject | Re: Fwd: [GIT PULL] timer changes for v3.10 |
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On 05/07/2013 02:31 PM, Pavel Machek wrote: > On Tue 2013-05-07 09:01:36, John Stultz wrote: >> On 05/06/2013 11:53 PM, Ingo Molnar wrote: >>> * Feng Tang <feng.tang@intel.com> wrote: >>> >>>>> 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.
> 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.
Sorry. You seem to not like the merged change, but I guess I'm not quite sure what exactly your objection is here.
thanks -john
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