Re: Fwd: [GIT PULL] timer changes for v3.10

[John Stultz <john.stultz@linaro.org>]

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