Anup Pemmaiah wrote: > Eric Saxe wrote: > >> The existing powertop implementation makes heavy use of /proc under >> Linux. >> For the necessary interfaces, here's what I'm thinking: >> >> - C-state information >> - Number of C-states, and amount of time system is spending in >> each one >> - Number of C-states can eventually be exported through a kstat. >> - Currently Solaris only supports C0, C1 states, so this can be >> hard-coded to start. >> - Amount of time spent in each C-state can be measured by a >> DTrace probe which fires >> during C-state transistions (around mwait, halt instruction >> invocations). >> - P-state information >> - Number of P-states, their frequencies, and amount of time >> system is spending in each one. >> - Number of P-states, frequencies, and current state already >> exported through cpu_info kstats. >> - Amount of time spent in each P-state can be meausured by a >> DTrace probe which fires >> when system changes CPU speed. >> >> > Similar to above information, was curious about T-State information. > The current cpu throttled percentage and the supported throttled > states being exported through cpu_info kstats. Measuring amount of > time spent in each T-state. I dont know how important it is, but just > thought of asking the alias. Yea, it's a good question. My impression of the T-states, is that in the general (common) case the system wouldn't use them, since from my understanding their purpose is mainly as a mechanism for quickly (and forcibly) throttling the processor clock to bring a thermal situation under control. It's also my understanding that the performance impact of the T-states are fairly severe, which begs the question if we would ever want the CPU to enter them when not idle. When the CPU is idle, I would wonder how T-states would compare to what we get from entering the C1 state. Since T-states don't change the voltage, I would guess that C1 would actually buy more. Maybe Aubrey or someone else can correct me if I'm mistaken...
Aren't there also cases where the processor could go into a T-state without the OS actually knowing? Thanks, -Eric
