On 09/18/2012 05:30 AM, Youquan Song wrote: >>> One case is turbostat utility (tools/power/x86/turbostat) at kernel 3.3 or early >>> . turbostat utility will read 10 registers one by one at Sandybridge, so it will >>> generate 10 IPIs to wake up idle CPUs. So cpuidle menu governor will predict it >>> is repeat mode and there is another IPI wake up idle CPU soon, so it keeps idle >>> CPU stay at C1 state even though CPU is totally idle. However, in the turbostat >>> , following 10 registers reading is sleep 5 seconds by default, so the idle CPU >>> will keep at C1 for a long time though it is idle until break event occurs. >>> In a idle Sandybridge system, run "./turbostat -v", we will notice that deep >>> C-state dangles between "70% ~ 99%". After patched the kernel, we will notice >>> deep C-state stays at >99.98%. >> >> Is there an impact on performances ? > > In this case, turbostat is utility to measure cpu idle status and itself > also is a workload to system. Its purpose is that show cpu C-state > information every 5 seconds. After patched the kernel, it also does > the same thing as usual. So I think the performance has no/little impact. > > I do not find performance impact in my tests. If you performance impact cases or > suggestions, I will be very glad to try. There is simple program [1] I wrote specifically for cpuidle. It does not do benchmarking. Maybe you can reuse it or modify it to fit your needs. Hope that helps. -- Daniel [1] http://git.linaro.org/gitweb?p=people/hongbozhang/pm-qa.git;a=blob;f=cpuidle/cpuidle_killer.c;h=5e7320f1e1679fdf4caa15d9b729534425b49bc6;hb=03e09b72a473032e434c811b2500f63fb65260c4 -- <http://www.linaro.org/> Linaro.org │ Open source software for ARM SoCs Follow Linaro: <http://www.facebook.com/pages/Linaro> Facebook | <http://twitter.com/#!/linaroorg> Twitter | <http://www.linaro.org/linaro-blog/> Blog -- To unsubscribe from this list: send the line "unsubscribe linux-acpi" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
