Is it possible to enable deeper c-states?

[Siarap]

Is it posible to enable deeper c-states than C3 in opnsense? My opnsense detects only C3 as deepest c-state. Is it something blocked? I think my intel i5-6500 supports deeper c-states. But maybe this is blocked in bios. My opnsense instance is installed on Hewlett Packard elite desk 800 g2 sff. Im currently using C3 c-state. And my elite desk power draw is about 18 watts when idle.

[dirtyfreebooter]

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sysctl hw.acpi.cpu.cx_lowest=Cmax

if you CPU supports it, you might also look at

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sysctl dev.hwpstate_intel.<cpu>.epp=[0-100]

https://man.freebsd.org/cgi/man.cgi?query=hwpstate_intel&sektion=4&format=html

I also found the most power savings by ensuring ASPM is enabled in BIOS for PCI devices (though if it makes things unstable, you often have to revert this)

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pciconf -lcv | grep ASPM

[Siarap]

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root@router:~ # pciconf -lcv | grep ASPM
                 link x4(x16) speed 5.0(8.0) ASPM L1(L0s/L1)
                 link x0(x1) speed 0.0(8.0) ASPM L0s/L1(L0s/L1)
                 link x0(x1) speed 0.0(8.0) ASPM L0s/L1(L0s/L1)
                 link x0(x4) speed 0.0(8.0) ASPM L0s/L1(L0s/L1)
                 link x4(x4) speed 5.0(5.0) ASPM L1(L0s/L1)
                 link x4(x4) speed 5.0(5.0) ASPM L1(L0s/L1)

hwpstate disabled for lower power draw

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sysctl dev.hwpstate_intel.<cpu>.epp=[0-100]
changes nothing even on 100 value. When hwpstate is enabled processor wont drop clocks lower than 1593mhz. After disabling it it drops clocks to 800mhz when idle.

after tunnable

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sysctl hw.acpi.cpu.cx_lowest=Cmaxi get this:

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root@router:~ # sysctl dev.cpu | grep cx
dev.cpu.3.cx_method: C1/mwait/hwc C2/mwait/hwc C3/mwait/hwc
dev.cpu.3.cx_usage_counters: 440 60 3436
dev.cpu.3.cx_usage: 11.17% 1.52% 87.29% last 177us
dev.cpu.3.cx_lowest: C8
dev.cpu.3.cx_supported: C1/1/1 C2/2/151 C3/3/256
dev.cpu.2.cx_method: C1/mwait/hwc C2/mwait/hwc C3/mwait/hwc
dev.cpu.2.cx_usage_counters: 400 100 3017
dev.cpu.2.cx_usage: 11.42% 2.84% 85.73% last 139us
dev.cpu.2.cx_lowest: C8
dev.cpu.2.cx_supported: C1/1/1 C2/2/151 C3/3/256
dev.cpu.1.cx_method: C1/mwait/hwc C2/mwait/hwc C3/mwait/hwc
dev.cpu.1.cx_usage_counters: 570 28 3431
dev.cpu.1.cx_usage: 14.14% 0.69% 85.15% last 133us
dev.cpu.1.cx_lowest: C8
dev.cpu.1.cx_supported: C1/1/1 C2/2/151 C3/3/256
dev.cpu.0.cx_method: C1/mwait/hwc C2/mwait/hwc C3/mwait/hwc
dev.cpu.0.cx_usage_counters: 4008 13899 35455
dev.cpu.0.cx_usage: 7.51% 26.04% 66.44% last 448us
dev.cpu.0.cx_lowest: C8
dev.cpu.0.cx_supported: C1/1/1 C2/2/151 C3/3/256


lowest is c8 but supported lowest c3 i dont know why.
Opnsense not supporting c-states deeper than C3?