Re: Extreme time jitter with suspend/resume cycles

[Thomas Gleixner <tglx@linutronix.de>]

On Thu, 5 Oct 2017, Thomas Gleixner wrote:
> On Wed, 4 Oct 2017, John Stultz wrote:
> > So, on resume when we call __timekeeping_inject_sleeptime(), that uses
> > the TK_CLEAR_NTP which clears the NTP state (sets STA_UNSYNC, etc) .
> > I'm not sure how else we can notify userspace.  It may be that ntpd
> > doesn't expect the kernel to set things as unsynced and doesn't
> > recover well, but the proper fix for that probably is in userspace.
> 
> Errm. No, __timekeeping_inject_sleeptime() only updates the timekeeper.

That should read:

     updates the timekeeper data fields, but does not call
     timekeeping_update().

> 
> We have two call sites:
> 
> timekeeping_resume()
> {
> 	.....
> 	if (sleeptime_injected)
> 		__timekeeping_inject_sleeptime(tk, &ts_delta);
> 	...
> 	timekeeping_update(tk, TK_MIRROR | TK_CLOCK_WAS_SET);
> 	...
> }
> 
> and
> 
> timekeeping_inject_sleeptime64()
> {
> 	__timekeeping_inject_sleeptime(tk, &delta);
> 	...
> 	timekeeping_update(tk, TK_CLEAR_NTP | TK_MIRROR | TK_CLOCK_WAS_SET);
> 	...
> }
> 
> But Gabriel talks about the effects from injecting sleep time in
> timekeeping_resume() because that's where we use
> read_persistent_clock64(). And there we don't clear NTP, unless there is
> some magic I'm missing completely.
> 
> Thanks,
> 
> 	tglx
> 
> 
>