On Mon, Jan 21, 2013 at 4:36 PM, John Stultz <john.stultz@xxxxxxxxxx> wrote:So the clocksource rating is supposed to be defined by the clocksource driver writer, and just provides a way for the clocksource core to select the best clocksource given a set of clocksources. It is not defined as any sort of calculated mapping to any property of the clocksource itself (although some driver writers might compute a ratings value in that way, but I feel the static ranking is much simpler). The comment above struct clocksource in clocksource.h tries to explain this.On 01/21/2013 01:14 PM, Matt Sealey wrote:Is that based on it's clocksource rating (probably worse than a realMy question really has to be is CONFIG_SCHED_HRTICK useful, what??? Not following this at all. jiffies is the *MOST* coarse resolution
exactly is it going to do on ARM here since nobody can ever have
enabled it? Is it going to keel over and explode if nobody registers a
non-jiffies sched_clock (since the jiffies clock is technically
reporting itself as a ridiculously high resolution clocksource..)?
clocksource there is (at least that I'm aware of.. I recall someone wanting
to do a 60Hz clocksource, but I don't think that ever happened).
hrtimer) or it's reported resolution? Because on i.MX51 if I force it
to use the jiffies clock the debug on the kernel log is telling me it
has a higher resolution (it TELLS me that it ticks "as fast" as the
CPU frequency and wraps less than my real timer).
I know where the 60Hz clocksource might come from, the old Amiga
platforms have one based on the PSU frequency (50Hz in Europe, 60Hz
US/Japan). Even a 60Hz clocksource is useful though (on the Amiga, at
least, it is precisely the vsync clock for synchronizing your display
output on TV-out, which makes it completely useful for the framebuffer
driver), but.. you just won't expect to assign it as sched_clock or
your delay timer. And if anyone does I'd expect they'd know full well
it'd not run so well.