On Thu, Sep 17, 2015 at 03:56:56PM +0100, Yingjoe Chen wrote: > On Thu, 2015-09-17 at 14:51 +0100, Sudeep Holla wrote: > > > > On 16/09/15 03:04, Yingjoe Chen wrote: > > > From: Daniel Kurtz <djkurtz@xxxxxxxxxxxx> > > > > > > Add device node to enable GPT timer. This timer will be > > > used as sched clock source. > > > > > > > Interesting any known issues with or advantage over the arch timers > > to prefer it as sched clock source. I see even arch timers are present > > in DT, hence the question. Or is it just a incorrect commit log ? > > > > How does this get selected as sched clock source ? I don't see > > sched_clock_register in mtk_timer.c > > > > To be clear, I am not against adding this timer support, but just want > > to know is it preferred for sched clock source ? if yes why ? better > > resolution ? > > Hi Sudeep, > > Thanks for your review. > > I hit the send too soon and missed cover letter, please see: > http://lists.infradead.org/pipermail/linux-mediatek/2015-September/002303.html > > The main reason to use GPT as sched clock is it won't stop during idle. You don't mean sched clock, you just mean a clock_event_device. A sched_clock is a high-precision clocksource that is read from (which by definition requires the CPUs to be non-idle). It doesn't have anything to do with interrupts and therefore cannot wake devices from idle. While the clock_event_device for the generic timer can't necessarily wake CPUs from idle. The generic timer system counter counts even if CPUs are idle, so the generic timer is fine as a sched_clock. Thanks, Mark. -- To unsubscribe from this list: send the line "unsubscribe devicetree" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
