On Sat, Jul 16, 2011 at 06:49:34PM -0400, Len Brown wrote: > From: Len Brown <len.brown@xxxxxxxxx> > Date: Mon, 6 Jun 2011 01:06:57 -0400 > > cpufreq offers the optional driver.get() entry point > for drivers to export instantaneous frequency in > /sys/devices/system/cpu/cpu*/cpufreq/cpuinfo_cur_freq. > > 25% of the acpi-cpufreq driver is involved in supporting > that optional feature, but on modern processors, it > is not reliable. > > So here we delete this optional feature from acpi-cpufreq. > /sys/devices/system/cpu/cpu*/cpufreq/cpuinfo_cur_freq > will go away on acpi-cpufreq systems, but note that > /sys/devices/system/cpu/cpu*/cpufreq/scaling_cur_freq > will still be presnet to indicate the most recent request. > > (and yes, powertop still works:-) > > The most common reason that driver.get() is not reliable > is that modern processors autonomously change frequency > without OS instruction. This means that reading > PERF_STATUS is possibly in-accurate as soon as the > instruction after it is read. > > Average frequency over an interval is more useful > than instantaneous frequency on modern hardware. > acpi-cpufreq supplies average frequency via > the the driver->getavg() entry, which is what > the ondemand governor uses. Regarding this patch and the philosophy behind it, I uphold my doubts which I specified last time this issue came up (cf. http://marc.info/?l=linux-acpi&m=130742534931688&w=2 ) Best, Dominik -- 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
