Le 24/02/2016 17:44, Romain Izard a écrit : > 2016-02-24 17:20 GMT+01:00 Sylvain Rochet <sylvain.roc...@finsecur.com>: >> Hi, >> >> On Wed, Feb 24, 2016 at 05:04:42PM +0100, Romain Izard wrote: >>> Register the counter of the Periodic Interval Timer as a possible >>> source for sched_clock. Keep the timer running even if the related >>> clockevent is disabled. >>> >>> This provides a better precision than the jiffies-based default. The >>> TCB clocksource does not work, as it is registered too late in the >>> initialization sequence. >> >> I have mixed feelings about that, but this is probably just a >> misunderstanding from my part. >> > My goal is to get a better precision on my printk and trace logs, > because the precision of jiffies is really very bad compared to > everything else I have encountered until now. But it looks like reading > a timer is quite complicated on AT91... > >> The PIT timer should not be used for systems with PM_SUSPEND enabled >> and used because it takes ages to synchronize on resume, how does this >> patch affect that ? >> >> Ref: commit ac34ad27fc ("clockevents: Do not suspend/resume if >> unused") > > So your advice would be to stay clear of the PIT, because it is > (globally) useless. > > I'll keep it in mind.
I tend to think like this as well. I would like to simplify our timer handling on AT91 and stick with TC for this purpose. It has de disadvantage of being obliged to use a TC(block) for clockevent/clocksource and loose it if we want to do something else with it but I do think that it's worth it. If you want a modified TC driver that registers sched_clock, we can provide you one as a workaround before that we rework the TC driver completely. It has it's own flaws (like re-using a compatible string or preventing the use of the "tclib") but is certainly handy. Bye, -- Nicolas Ferre