On Wed, Aug 18, 2010 at 11:12 AM, J. Bruce Fields <bfields@xxxxxxxxxxxx> wrote: > I'm completely ignorant about higher-resolution time sources. Any > recommended reading? What resolution do they actually provide, what's > the expense of reading them, how reliable are they, and how do the > answers to those questions vary across different hardware and kernel > versions? A quick look at drivers/clocksource/ doesn't suggest > simple answers. Yea, there aren't simple answers. Clocksource hardware varies drastically in resolution and access time across systems and architectures. Further, clocksources may change while the system is up, so we don't really expose the hardware resolution. On x86, access latency varies from ~50ns (TSC) to ~1.3us (ACPI PM). (And that is ignoring the PIT, which can be 18us per call - luckily almost no hardware uses that). The resolution similarly scales from sub-ns (TSC @ > 1ghz cpus) to ~279ns (ACPI PM). Of course, across architectures you will see even more variance. thanks -john -- To unsubscribe from this list: send the line "unsubscribe linux-nfs" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
