Re: [PATCH 2/2] platform/x86/amd/hfi: Enforce Zen 5 vs Zen 5c asymmetric capacity and V/F knee ceiling on Krackan Point

[Mario Limonciello <mario.limonciello@amd.com>]

On 11/12/26 19:26, Aiden Hecker wrote:
> When `amd_hfi` (`AMDI0104:00`) initializes on AMD Family 1Ah Model 60h
> (Ryzen AI 7 350), the SMU populates 3 workload classes in shared memory.
> However, high-entropy interactive threads can still suffer either:
>    1. Cross-core placement onto odd Zen 5c cores (CPUs 1,3,5,7,9,11,13,15)
>       when `cpu_scale` is not synchronized with HFI class 0 rankings, or
>    2. Quadratic voltage wall dissipation ("excess potential") when boosting
>       from the V/F efficiency knee (CPPC 168 / 4364 MHz @ 1.07V on Zen 5;
>       CPPC 116 / 3013 MHz @ 0.94V on Zen 5c) to the upper voltage barrier
>       (CPPC 208 / 5091 MHz @ 1.38V), where +14% frequency costs +67% more
>       energy per instruction (996.1 pJ/instr vs 595.5 pJ/instr).
> 
> Synchronize `amd_hfi` initialization with per-CPU `cpu_scale` and expose a
> module parameter `vf_knee_clamp` (default enabled on battery / balanced EPP)
> to right-size CPPC `des_perf` / `max_perf` below the cubic voltage wall.
> 
> Assisted-by: Antigravity (Google DeepMind)
> Tested-by: Aiden Hecker <heckeraiden@gmail.com>
> Signed-off-by: Aiden Hecker <heckeraiden@gmail.com>
> ---
>   drivers/platform/x86/amd/hfi/hfi.c | 42 ++++++++++++++++++++++++++++++
>   1 file changed, 42 insertions(+)
> 
> diff --git a/drivers/platform/x86/amd/hfi/hfi.c b/drivers/platform/x86/amd/hfi/hfi.c
> index 19c42e88a310..7e91f0a21455 100644
> --- a/drivers/platform/x86/amd/hfi/hfi.c
> +++ b/drivers/platform/x86/amd/hfi/hfi.c
> @@ -24,6 +24,8 @@
>   #include <linux/platform_device.h>
>   #include <linux/smp.h>
>   #include <linux/workqueue.h>
> +#include <linux/arch_topology.h>
> +#include <asm/topology.h>
>   
>   #define AMD_HFI_DRIVER		"amd_hfi"
>   #define AMD_HFI_MAX_CLASSES	3
> @@ -31,6 +33,15 @@
>   #define ZEN5_MAX_CPPC_PERF	208U
>   #define ZEN5_VF_KNEE_CPPC_AC	168U /* 4364 MHz @ 1.07V (-40.2% pJ/instr vs 1.38V wall) */
>   #define ZEN5C_VF_KNEE_CPPC_AC	116U /* 3013 MHz @ 0.94V */
> +
> +static bool vf_knee_clamp = true;
> +module_param(vf_knee_clamp, bool, 0644);
> +MODULE_PARM_DESC(vf_knee_clamp,
> +		 "Clamp non-turbo bursts at the CMOS V/F efficiency knee to avoid quadratic pJ/instr overdrive");
> +
> +static void amd_hfi_sync_hetero_capacity(void)
> +{
> +	int cpu;
> +
> +	for_each_online_cpu(cpu) {
> +		u32 eax = 0, ebx = 0, ecx = 0, edx = 0;
> +		u32 core_type;
> +
> +		cpuid_count(0x80000026, 0, &eax, &ebx, &ecx, &edx);
> +		core_type = (ebx >> 28) & 0xF;
> +
> +		if (core_type == 0) {
> +			/* High-Entropy Zen 5 Core */
> +			unsigned long cap = (cpu < 8) ? 1024UL : 840UL;
> +			WRITE_ONCE(per_cpu(cpu_scale, cpu), cap);
> +			sched_set_itmt_core_prio((cpu < 8) ? 208 : 172, cpu);
> +		} else {
> +			/* Low-Entropy Zen 5c Core */
> +			unsigned long cap = (cpu < 8) ? 664UL : 512UL;
> +			WRITE_ONCE(per_cpu(cpu_scale, cpu), cap);
> +			sched_set_itmt_core_prio((cpu < 8) ? 135 : 105, cpu);
> +		}
> +	}
> +	sched_set_itmt_support();
> +}

Similar feedback to your other patch.  You should use existing defined 
feature flags and topology information.  You also can't assume that the 
world is made of Zen5 cores.  Things aren't the same on newer 
microarchitectures.