On Mon, Jan 21, 2013 at 6:51 PM, John Stultz <john.stu...@linaro.org> wrote: > On 01/21/2013 02:54 PM, Matt Sealey wrote: >> >> On Mon, Jan 21, 2013 at 4:36 PM, John Stultz <john.stu...@linaro.org> >> wrote: >>> >>> On 01/21/2013 01:14 PM, Matt Sealey wrote: > > As far as jiffies rating, from jiffies.c: > .rating = 1, /* lowest valid rating*/ > > So I'm not sure what you mean by "the debug on the kernel log is telling me > it has a higher resolution".
Oh, it is just if I actually don't run setup_sched_clock on my platform, it gives a little message (with #define DEBUG 1 in sched_clock.c) about who setup the last sched_clock. Since you only get one chance, and I was fiddling with setup_sched_clock being probed from multiple possible timers from device tree (i.MX3 has a crapload of valid timers, which one you use right now is basically forced by the not-quite-fully-DT-only code and some funky iomap tricks). And what I got was, if I use the real hardware timer, it runs at 66MHz and says it has 15ns resolution and wraps every 500 seconds or so. The jiffies timer says it's 750MHz, with a 2ns resoluton.. you get the drift. The generic reporting of how "good" the sched_clock source is kind of glosses over the quality rating of the clock source and at first glance (if you're not paying that much attention), it is a little bit misleading.. > Yes, in the case I was remembering, the 60HZ was driven by the electrical > line. While I have your attention, what would be the minimum "good" speed to run the sched_clock or delay timer implementation from? My rudimentary scribblings in my notebook give me a value of "don't bother" with less than 10KHz based on HZ=100, so I'm wondering if a direct 32.768KHz clock would do (i.MX osc clock input if I can supply it to one of the above myriad timers) since this would be low-power compared to a 66MHz one (by a couple mA anyway). I also have a bunch of questions about the delay timer requirements.. I might mail you personally.. or would you prefer on-list? -- Matt Sealey <m...@genesi-usa.com> Product Development Analyst, Genesi USA, Inc. -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
