[Bug 234733] Setting CPU frequency with sysctl dev.cpu.0.fr slows a Ryzen 2700X down

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https://bugs.freebsd.org/bugzilla/show_bug.cgi?id=234733

--- Comment #10 from sigsys at gmail.com ---
(In reply to Conrad Meyer from comment #9)

It's showing some interesting behavior I think.  The last 3 bits of 0xc0010061
and 0xc0010062 go up but don't go down.  And they go up together.


At boot:

# cpucontrol -m '0xc0010061' /dev/cpuctl0
MSR 0xc0010061: 0x00000000 0x00000020
# cpucontrol -m '0xc0010062' /dev/cpuctl0
MSR 0xc0010062: 0x00000000 0x00000000


After dev.cpu.0.freq=3200 (max):

# cpucontrol -m '0xc0010061' /dev/cpuctl0
MSR 0xc0010061: 0x00000000 0x00000020
# cpucontrol -m '0xc0010062' /dev/cpuctl0
MSR 0xc0010062: 0x00000000 0x00000000

(No change there.)


After dev.cpu.0.freq=2800:

# cpucontrol -m '0xc0010061' /dev/cpuctl0
MSR 0xc0010061: 0x00000000 0x00000021
# cpucontrol -m '0xc0010062' /dev/cpuctl0
MSR 0xc0010062: 0x00000000 0x00000001


After dev.cpu.0.freq=1500:

# cpucontrol -m '0xc0010061' /dev/cpuctl0
MSR 0xc0010061: 0x00000000 0x00000022
# cpucontrol -m '0xc0010062' /dev/cpuctl0
MSR 0xc0010062: 0x00000000 0x00000002


After dev.cpu.0.freq=3200 (trying to set it back to max):

# cpucontrol -m '0xc0010061' /dev/cpuctl0
MSR 0xc0010061: 0x00000000 0x00000022
# cpucontrol -m '0xc0010062' /dev/cpuctl0
MSR 0xc0010062: 0x00000000 0x00000002

And performance is still as if it were at 1500.


After cpucontrol -m '0xc0010062=0x0' on all CPUs:

# cpucontrol -m '0xc0010061' /dev/cpuctl0
MSR 0xc0010061: 0x00000000 0x00000020
# cpucontrol -m '0xc0010062' /dev/cpuctl0
MSR 0xc0010062: 0x00000000 0x00000000

And now performance is back to what it was at 3200!  I didn't manually try to
reset 0xc0010061, it already reverted back to its initial value after changing
0xc0010062.

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