On 01/14/2014 10:10 AM, Preeti U Murthy wrote: > Hi Steven, > > On 01/14/2014 08:06 PM, Steven Pratt wrote: >> I am looking for info on when and how we are able to disable power saving >> features of current (P7, P7+) chips in order to reduce latency. This is >> often done in latency sensitive applications when power consumption is not >> an issue. On Intel boxes we can disable P-state frequency changes as well as >> disabling C-State or sleep state changes. In fact we can control how deep a >> sleep the processor can go into. I know we have control Dynamic Processor >> Scaling and Idle Power Savings, but what states do these really affect? Can >> I really disable Nap mode of a processor? If so how? Can I disable even the >> lightest winkle mode? Looking for current information (read RHEL 6 and >> SLES11), future changes are interesting. >> >> Steve > I can answer this question with respect to cpuidle on PowerNV platforms. > > 1. In order to disable cpuidle states management altogether, one can > pass the powersave=off kernel cmd line parameter during boot up of the > kernel. This will ensure that each time a CPU has nothing to do, it can > enter low thread priority which could lower power consumption to some > extent but is not expected to hit latency of applications noticeably. > > 2. In order to exactly control the cpuidle states into which idle CPUs > can enter into during runtime, one can make use of the sysfs files under: > /sys/devices/system/cpu/cpux/cpuidle/statex/disable option to > selectively disable any state. > > However if one is using the menu cpuidle governor, disabling an idle > state does not disable the idle states which are deeper than it. They > continue to remain active unless they are specifically disabled. What > this means is that one cannot control the depth of the idle states > available for a CPU, although we can control the exact idle states > available for a processor. > > But if the ladder governor is used, one can control the depth of the > idle states that a CPU can enter into. The governor can be chosen by > echoing either menu/ladder to > /sys/devices/system/cpu/cpuidle/current_governor_ro. The cpuidle > governor takes decisions about the idle state for a cpu to enter into > depending on its idle history. The popular governor used by most archs > is the menu governor. > > Hence nap/sleep/winkle any of these states can be disabled. The code > which enables the above mentioned functionalities on powernv is yet to > go upstream although the same is already upstream and can be used for > the pseries platform to disable/enable the idle states on it. > > Today on powernv the default idle state nap is entered into all the > time. One can disable it by echoing 0 to powersave_nap under > /proc/sys/kernel/powersave_nap, in which case the cpu enters low thread
Thanks, that is great information going forward, now I just need info on what works today in PowerVM. Steve > priority. > > Thanks > > Regards > Preeti U Murthy > >> _______________________________________________ >> Linuxppc-dev mailing list >> Linuxppc-dev@lists.ozlabs.org >> https://lists.ozlabs.org/listinfo/linuxppc-dev >> _______________________________________________ Linuxppc-dev mailing list Linuxppc-dev@lists.ozlabs.org https://lists.ozlabs.org/listinfo/linuxppc-dev
