> > 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. Thanks -Youquan -- 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
