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Anastasios Koutian has posted comments on this change by Anastasios Koutian. ( https://review.coreboot.org/c/coreboot/+/83270?usp=email )
Change subject: cpu/intel/model_206ax: Allow package power limit clamping ......................................................................
Patch Set 5:
(1 comment)
Commit Message:
https://review.coreboot.org/c/coreboot/+/83270/comment/b8ce70dd_bedc6440?usp... : PS5, Line 8:
Please explain what it does. […]
From "Intel® 64 and IA-32 Architectures Software Developer’s Manual Volume 3B: System Programming Guide, Part 2", section 14.9.3, page 14-33:
"Package Clamping Limitation #1 (bit 16): Allow going below OS-requested P/T state setting during time window specified by bits 23:17." "Package Clamping Limitation #2 (bit 48): Allow going below OS-requested P/T state setting during time window specified by bits 23:17."
So basically it turns PL1/PL2 respectively into a hard constraint and slows down the CPU a much as possible in order to satisfy the power limit.
If, for example, PL1 clamp is disabled, the CPU might decide to exceed PL1. Same for PL2.
I tested this with the i7-3940XM, by running a combined stress test for CPU cores and integrated graphics:
`$ stress-ng -c 8 --cpu-method matrixprod` `$ furmark --fullscreen --p1080 --demo furmark-gl`
With the PL1 clamp disabled, after several minutes of running the two commands simultaneously, the core frequency is 3.0 GHz, graphics frequency is 650 MHz, and package power consumption levels out at ~42 W, which means that the CPU decides to violate the PL1 = 35 W constraint.
When the PL1 clamp is enabled, for the same stress test, core frequency is 2.7 GHz, graphics are at 540 MHz, and package power stabilises at 35 W, which means that PL1 is being enforced.