>> i am curious, do the values of CONFIG_HZ and CONFIG_NO_HZ somehow affect the >> scheduling latency (as reported by cyclictest) of a real-time/vanilla kernel, >> especially when CONFIG_HIGH_RES_TIMERS is enabled? > > CONFIG_HZ should be pretty irrelevant, but CONFIG_NO_HZ=y especially > when the CPU does support deeper C-States and the ACPI cpuidle support > is active may influence it simply because the wake up from deeper > c-states can take significantly longer than waking up from C1 (the > default halt state). Note that the wakeup latency from C-States > depends on the CPU model, chipset, available timer hardware ... interesting ... from my understanding, the wakeup latency is known to the kernel (/sys/devices/system/cpu/cpuX/cpuidle/stateY/latency) and is taken into account when governor selects the next state ... is it possible to tweak the governor by setting the latency requirement (pm_qos_requirement(PM_QOS_CPU_DMA_LATENCY)) from userspace? thanks, tim -- tim@xxxxxxxxxx http://tim.klingt.org Lesser artists borrow, great artists steal. Igor Stravinsky
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