Re: [PATCH 5/8] x86/amd: Detect preferred cores in amd_get_boost_ratio_numerator()

[Mario Limonciello <mario.limonciello@xxxxxxx>]

On 8/27/2024 10:43, Gautham R. Shenoy wrote:
> On Mon, Aug 26, 2024 at 04:13:55PM -0500, Mario Limonciello wrote:
> > From: Mario Limonciello <mario.limonciello@xxxxxxx>
> >
> > AMD systems that support preferred cores will use "166" as their
> > numerator for max frequency calculations instead of "255".
> >
> > Add a function for detecting preferred cores by looking at the
> > highest perf value on all cores.
> >
> > If preferred cores are enabled return 166 and if disabled the
> > value in the highest perf register. As the function will be called
> > multiple times, cache the values for the boost numerator and if
> > preferred cores will be enabled in global variables.
> >
> > Signed-off-by: Mario Limonciello <mario.limonciello@xxxxxxx>
> > ---
>
> [..snip..]
>
> >   /**
> >    * amd_get_boost_ratio_numerator: Get the numerator to use for boost ratio calculation
> >    * @cpu: CPU to get numerator for.
> > @@ -162,20 +232,19 @@ EXPORT_SYMBOL_GPL(amd_get_highest_perf);
> >    */
> >   int amd_get_boost_ratio_numerator(unsigned int cpu, u64 *numerator)
> >   {
> > -	struct cpuinfo_x86 *c = &boot_cpu_data;
> > +	bool prefcore;
> > +	int ret;
> >   
> > -	if (c->x86 == 0x17 && ((c->x86_model >= 0x30 && c->x86_model < 0x40) ||
> > -			       (c->x86_model >= 0x70 && c->x86_model < 0x80))) {
> > -		*numerator = 166;
> > -		return 0;
> > -	}
> > +	ret = amd_detect_prefcore(&prefcore);
> > +	if (ret)
> > +		return ret;
> >   
> > -	if (c->x86 == 0x19 && ((c->x86_model >= 0x20 && c->x86_model < 0x30) ||
> > -			       (c->x86_model >= 0x40 && c->x86_model < 0x70))) {
> > -		*numerator = 166;
> > +	/* without preferred cores, return the highest perf register value */
> > +	if (!prefcore) {
> > +		*numerator = boost_numerator;
> >   		return 0;
> >   	}
> > -	*numerator = 255;
> > +	*numerator = CPPC_HIGHEST_PERF_PREFCORE;
>
>
> Interesting. So even when the user boots a system that supports
> preferred-cores with "amd_preferred=disable",
> amd_get_boost_ratio_numerator() will return CPPC_HIGHEST_PERF_PREFCORE
> as the call prefcore == true here.
>
> I suppose that is as intended, since even though the user may not want
> to use the preferred core logic for task-scheduling/load-balancing,
> the numerator for the boost-ratio is purely dependent on the h/w
> capability.
>
> Is this understanding correct? If so, can this be included as a
> comment in the code ?

Yup, you got it all right.  I'll fold some of this into the function 
comment for v2.

> The rest of the patch looks good to me.
>
> Reviewed-by: Gautham R. Shenoy <gautham.shenoy@xxxxxxx>
>
> --
> Thanks and Regards
> gautham.
>
>
>
> >   
> >   	return 0;
> >   }
> > diff --git a/drivers/cpufreq/amd-pstate.c b/drivers/cpufreq/amd-pstate.c
> > index f470b5700db58..ec32c830abc1d 100644
> > --- a/drivers/cpufreq/amd-pstate.c
> > +++ b/drivers/cpufreq/amd-pstate.c
> > @@ -807,32 +807,18 @@ static DECLARE_WORK(sched_prefcore_work, amd_pstste_sched_prefcore_workfn);
> >   
> >   static void amd_pstate_init_prefcore(struct amd_cpudata *cpudata)
> >   {
> > -	int ret, prio;
> > -	u32 highest_perf;
> > -
> > -	ret = amd_get_highest_perf(cpudata->cpu, &highest_perf);
> > -	if (ret)
> > +	/* user disabled or not detected */
> > +	if (!amd_pstate_prefcore)
> >   		return;
> >   
> >   	cpudata->hw_prefcore = true;
> > -	/* check if CPPC preferred core feature is enabled*/
> > -	if (highest_perf < CPPC_MAX_PERF)
> > -		prio = (int)highest_perf;
> > -	else {
> > -		pr_debug("AMD CPPC preferred core is unsupported!\n");
> > -		cpudata->hw_prefcore = false;
> > -		return;
> > -	}
> > -
> > -	if (!amd_pstate_prefcore)
> > -		return;
> >   
> >   	/*
> >   	 * The priorities can be set regardless of whether or not
> >   	 * sched_set_itmt_support(true) has been called and it is valid to
> >   	 * update them at any time after it has been called.
> >   	 */
> > -	sched_set_itmt_core_prio(prio, cpudata->cpu);
> > +	sched_set_itmt_core_prio((int)READ_ONCE(cpudata->highest_perf), cpudata->cpu);
> >   
> >   	schedule_work(&sched_prefcore_work);
> >   }
> > @@ -998,12 +984,12 @@ static int amd_pstate_cpu_init(struct cpufreq_policy *policy)
> >   
> >   	cpudata->cpu = policy->cpu;
> >   
> > -	amd_pstate_init_prefcore(cpudata);
> > -
> >   	ret = amd_pstate_init_perf(cpudata);
> >   	if (ret)
> >   		goto free_cpudata1;
> >   
> > +	amd_pstate_init_prefcore(cpudata);
> > +
> >   	ret = amd_pstate_init_freq(cpudata);
> >   	if (ret)
> >   		goto free_cpudata1;
> > @@ -1453,12 +1439,12 @@ static int amd_pstate_epp_cpu_init(struct cpufreq_policy *policy)
> >   	cpudata->cpu = policy->cpu;
> >   	cpudata->epp_policy = 0;
> >   
> > -	amd_pstate_init_prefcore(cpudata);
> > -
> >   	ret = amd_pstate_init_perf(cpudata);
> >   	if (ret)
> >   		goto free_cpudata1;
> >   
> > +	amd_pstate_init_prefcore(cpudata);
> > +
> >   	ret = amd_pstate_init_freq(cpudata);
> >   	if (ret)
> >   		goto free_cpudata1;
> > @@ -1903,6 +1889,12 @@ static int __init amd_pstate_init(void)
> >   		static_call_update(amd_pstate_update_perf, cppc_update_perf);
> >   	}
> >   
> > +	if (amd_pstate_prefcore) {
> > +		ret = amd_detect_prefcore(&amd_pstate_prefcore);
> > +		if (ret)
> > +			return ret;
> > +	}
> > +
> >   	/* enable amd pstate feature */
> >   	ret = amd_pstate_enable(true);
> >   	if (ret) {
> > diff --git a/include/acpi/cppc_acpi.h b/include/acpi/cppc_acpi.h
> > index 2246ce0630362..1d79320a23490 100644
> > --- a/include/acpi/cppc_acpi.h
> > +++ b/include/acpi/cppc_acpi.h
> > @@ -137,10 +137,12 @@ struct cppc_cpudata {
> >   };
> >   
> >   #ifdef CONFIG_CPU_SUP_AMD
> > +extern int amd_detect_prefcore(bool *detected);
> >   extern int amd_get_highest_perf(unsigned int cpu, u32 *highest_perf);
> >   extern int amd_get_boost_ratio_numerator(unsigned int cpu, u64 *numerator);
> >   #else /* !CONFIG_CPU_SUP_AMD */
> >   static inline int amd_get_highest_perf(unsigned int cpu, u32 *highest_perf) { return -ENODEV; }
> > +static inline int amd_detect_prefcore(bool *detected) { return -ENODEV; }
> >   static inline int amd_get_boost_ratio_numerator(unsigned int cpu, u64 *numerator) { return -ENODEV; }
> >   #endif /* !CONFIG_CPU_SUP_AMD */
> >   
> > --
> > 2.43.0