What does _ACPI suffix mean?

[Daniel15]

One system gives me output like this:

           Pkg(HW)  |            Core(HW) |            CPU(OS) 0
                    |                     | C0 active   2.8%
                    |                     | POLL        0.0%    0.0 ms
                    |                     | C1          1.1%    0.4 ms
C2 (pc2)    7.2%    |                     |
C3 (pc3)    5.5%    | C3 (cc3)    0.0%    | C3          0.1%    0.1 ms
C6 (pc6)    1.5%    | C6 (cc6)    1.9%    | C6          2.2%    0.6 ms
C7 (pc7)   75.2%    | C7 (cc7)   92.8%    | C7s         0.0%    0.0 ms
C8 (pc8)    0.0%    |                     | C8         21.5%    2.5 ms
C9 (pc9)    0.0%    |                     | C9          0.0%    0.0 ms
C10 (pc10)  0.0%    |                     |
                    |                     | C10        72.8%   12.5 ms
                    |                     | C1E         0.4%    0.2 ms

                    |            Core(HW) |            CPU(OS) 1

while another gives output like this:

           Pkg(HW)  |            Core(HW) |            CPU(OS) 0   CPU(OS) 1
                    |                     | C0 active   5.9%        0.9%
                    |                     | POLL        0.1%    0.0 ms  0.0%    0.0 ms
                    |                     | C1_ACPI    14.2%    0.2 ms  1.0%    0.1 ms
C2 (pc2)    0.0%    |                     | C2_ACPI    39.2%    0.8 ms 27.0%    0.9 ms
C3 (pc3)    0.0%    | C3 (cc3)    0.0%    | C3_ACPI    33.6%    1.2 ms 69.7%    3.0 ms
C6 (pc6)    0.0%    | C6 (cc6)    1.1%    |
C7 (pc7)    0.0%    | C7 (cc7)    0.0%    |
C8 (pc8)    0.0%    |                     |
C9 (pc9)    0.0%    |                     |
C10 (pc10)  0.0%    |                     |

                    |            Core(HW) |            CPU(OS) 2   CPU(OS) 3

What's the difference between "C3" and "C3_ACPI", and why would the second system have fewer states? (first one is an i5-9500 while the second one is an i5-13500, both with C-states enabled in the BIOS)

[fenrus75]

it means your kernel does not have intel_idle support for your CPU ... which is unusually unless you're running an older kernel on newer hardware

On Mon, Oct 30, 2023 at 3:20 PM Daniel Lo Nigro @.***> wrote:

One system gives me output like this:

       Pkg(HW)  |            Core(HW) |            CPU(OS) 0
                |                     | C0 active   2.8%
                |                     | POLL        0.0%    0.0 ms
                |                     | C1          1.1%    0.4 ms

C2 (pc2) 7.2% | | C3 (pc3) 5.5% | C3 (cc3) 0.0% | C3 0.1% 0.1 ms C6 (pc6) 1.5% | C6 (cc6) 1.9% | C6 2.2% 0.6 ms C7 (pc7) 75.2% | C7 (cc7) 92.8% | C7s 0.0% 0.0 ms C8 (pc8) 0.0% | | C8 21.5% 2.5 ms C9 (pc9) 0.0% | | C9 0.0% 0.0 ms C10 (pc10) 0.0% | | | | C10 72.8% 12.5 ms | | C1E 0.4% 0.2 ms

                |            Core(HW) |            CPU(OS) 1

while another gives output like this:

       Pkg(HW)  |            Core(HW) |            CPU(OS) 0   CPU(OS) 1
                |                     | C0 active   5.9%        0.9%
                |                     | POLL        0.1%    0.0 ms  0.0%    0.0 ms
                |                     | C1_ACPI    14.2%    0.2 ms  1.0%    0.1 ms

C2 (pc2) 0.0% | | C2_ACPI 39.2% 0.8 ms 27.0% 0.9 ms C3 (pc3) 0.0% | C3 (cc3) 0.0% | C3_ACPI 33.6% 1.2 ms 69.7% 3.0 ms C6 (pc6) 0.0% | C6 (cc6) 1.1% | C7 (pc7) 0.0% | C7 (cc7) 0.0% | C8 (pc8) 0.0% | | C9 (pc9) 0.0% | | C10 (pc10) 0.0% | |

                |            Core(HW) |            CPU(OS) 2   CPU(OS) 3

What's the difference between "C3" and "C3_ACPI", and why would the second system have fewer states? (first one is an i5-9500 while the second one is an i5-13500, both with C-states enabled in the BIOS)

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[Daniel15]

Hmm, that's interesting, because it does seem like intel_idle is active?

root@DanHome:~# cat /sys/devices/system/cpu/cpuidle/current_driver
intel_idle

It's an i5-13500 running on Linux 6.1.38. I'll have to figure out how to investigate this more. Can any of the cpufreq settings affect this?

[fenrus75]

intel_idle can fall back to ACPI -- but that does not mean it knows your hardware. Is this by chance new hardware ? (newer than the 6.1 kernel which is basically a year old by now)

On Mon, Oct 30, 2023 at 4:54 PM Daniel Lo Nigro @.***> wrote:

Hmm, that's interesting, because it does seem like intel_idle is active?

@.***:~# cat /sys/devices/system/cpu/cpuidle/current_driver intel_idle

It's an i5-13500 running on Linux 6.1.38. I'll have to figure out how to investigate this more. Can any of the cpufreq settings affect this?

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[Daniel15]

Hey @fenrus75, sorry for the delay in replying. This is somewhat recent hardware - it's a W680 motherboard with a Raptor Lake CPU (i5-13500).

I did notice that intel_idle.c seems to have cases for ALDERLAKE and ALDERLAKE_L but not RAPTORLAKE: https://github.com/torvalds/linux/blob/052d534373b7ed33712a63d5e17b2b6cdbce84fd/drivers/idle/intel_idle.c#L1530

[Daniel15]

Confirmed that intel_idle doesn't currently support Raptor Lake CPUs, as per this mailing list post from August 2023: https://lore.kernel.org/linux-pm/7e2c1da24b48217045e8ad95b739ec96cdce5931.camel@intel.com/