I am trying to get a better understanding of CPU power management. For the purposes of this discussion I have an i5-2500K running in a desktop environment.
If I leave my computer on 24/7 downloading torrent files (a relatively low CPU intensive activity) what processor states will my CPU be in?
C0 is the operating state.
C1 (often known as Halt) is a state where the processor is not executing instructions, but can return to an executing state essentially instantaneously.
C2 (often known as Stop-Clock) is a state where the processor maintains all software-visible state, but may take longer to wake up.
C3 (often known as Sleep) is a state where the processor does not need to keep its cache coherent.
I would assume that 3 of the 4 cores would be in the C1 state and the 4th core which is actually running the torrent program and network overhead would be in the C0 state. Is this true? States C2 and C3 seem more like states for laptop environments than the desktop. I know that I can set my desktop to sleep, but I have this setting disabled. I presume that means my CPU should never reach the C3 state. But what about C2? Is that possible? How can you tell which state each core is currently in?
Next how does this flow into SpeedStep? I know that SpeedStep allows the cores to reach different Performance States (P0, P1, P2, ...). I am not sure what the lowest P-State is for the i5-2500K but it seems possible for a core to be in any P-State while in the C0 state, but would have to be in the lowest P-State if it was in the C1 or C2 state. Is this true? Once the CPU reaches the C3 state is it still in a P-State or does that no longer apply?
How do these things interact within a multicore CPU? Although it is possible for one core to be in the C0 state and others to be in the C1 state. Is the same true for C2 or C3? Or once the CPU reaches the C3 state the entire CPU is put to sleep?
Next Power Gating. I understand (at a very high level) what power gating is, but when does it happen with regard to the C-states listed above? I am not using the iGPU of the i5-2500K so I would assume that the iGPU is always power gated. What C-state would a core have to reach before it would be "power gated"? Is a core being power gated equivalent to being in the C2 state?
Thanks for any info on this...
If I leave my computer on 24/7 downloading torrent files (a relatively low CPU intensive activity) what processor states will my CPU be in?
C0 is the operating state.
C1 (often known as Halt) is a state where the processor is not executing instructions, but can return to an executing state essentially instantaneously.
C2 (often known as Stop-Clock) is a state where the processor maintains all software-visible state, but may take longer to wake up.
C3 (often known as Sleep) is a state where the processor does not need to keep its cache coherent.
I would assume that 3 of the 4 cores would be in the C1 state and the 4th core which is actually running the torrent program and network overhead would be in the C0 state. Is this true? States C2 and C3 seem more like states for laptop environments than the desktop. I know that I can set my desktop to sleep, but I have this setting disabled. I presume that means my CPU should never reach the C3 state. But what about C2? Is that possible? How can you tell which state each core is currently in?
Next how does this flow into SpeedStep? I know that SpeedStep allows the cores to reach different Performance States (P0, P1, P2, ...). I am not sure what the lowest P-State is for the i5-2500K but it seems possible for a core to be in any P-State while in the C0 state, but would have to be in the lowest P-State if it was in the C1 or C2 state. Is this true? Once the CPU reaches the C3 state is it still in a P-State or does that no longer apply?
How do these things interact within a multicore CPU? Although it is possible for one core to be in the C0 state and others to be in the C1 state. Is the same true for C2 or C3? Or once the CPU reaches the C3 state the entire CPU is put to sleep?
Next Power Gating. I understand (at a very high level) what power gating is, but when does it happen with regard to the C-states listed above? I am not using the iGPU of the i5-2500K so I would assume that the iGPU is always power gated. What C-state would a core have to reach before it would be "power gated"? Is a core being power gated equivalent to being in the C2 state?
Thanks for any info on this...