On 14/05/2015 13:54, Viresh Kumar wrote: > Mason wrote: > >> I'm using a 27 MHz crystal as clocksource. This is independent >> of the CPU frequency. However, I'm using the ARM TWD as the >> system's clockevent source, and the TWD's clock is tied to >> the CPU clock (PERIPHCLK = CPUCLK / 2 on this SoC). > > The only (very straight forward) problem is that we aren't propagating > the freq update to clockevents core and you need to debug a bit there. I had the same thought, which is why I added the "NEW RATE" trace. > Also I wanted to see the source of your print message: > [ 19.650454] NEW RATE=9250000 > [ 19.653644] NEW RATE=9250000 > > What's this rate ? Old/new ? Because you are at least printing the old > rate here, and the function by default gets the new rate. I added a printk inside twd_update_frequency(). http://lxr.free-electrons.com/source/arch/arm/kernel/smp_twd.c?v=3.14#L107 I inserted printk("NEW RATE=%lu\n", twd_timer_rate); right before the call to clockevents_update_freq(). When I execute "echo 18500 > scaling_max_freq" the system is supposed to change the CPU frequency to 18.5 MHz (I might have a bug lurking there) and PERIPHCLK is 1/2 of that, i.e 9.25 MHz. twd_update_frequency() is called twice: once for each CPU. (The timers are local to each CPU.) >> I'm wondering if there's another standard clockevent source >> I could try (it would be great if it supported high-resolution >> timers). > > I hope you have some platform general-purpose-timers. Yes, I do, but I was trying to use as much generic code as possible to limit the chances of introducing bugs. I'll take a fresh look at the ARM GLOBAL TIMER, but last I checked, it didn't seem to handle frequency scaling. Regards. -- To unsubscribe from this list: send the line "unsubscribe cpufreq" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
