linux-kernel - Re: [PATCH V5 3/7] cpufreq: amd-pstate: Enable amd-pstate preferred core supporting.

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Message-ID: <20230908131702.GF19320@noisy.programming.kicks-ass.net>
Date:   Fri, 8 Sep 2023 15:17:02 +0200
From:   Peter Zijlstra <peterz@...radead.org>
To:     Meng Li <li.meng@....com>
Cc:     "Rafael J . Wysocki" <rafael.j.wysocki@...el.com>,
        Huang Rui <ray.huang@....com>, linux-pm@...r.kernel.org,
        linux-kernel@...r.kernel.org, x86@...nel.org,
        linux-acpi@...r.kernel.org, Shuah Khan <skhan@...uxfoundation.org>,
        linux-kselftest@...r.kernel.org,
        Nathan Fontenot <nathan.fontenot@....com>,
        Deepak Sharma <deepak.sharma@....com>,
        Alex Deucher <alexander.deucher@....com>,
        Mario Limonciello <mario.limonciello@....com>,
        Shimmer Huang <shimmer.huang@....com>,
        Perry Yuan <Perry.Yuan@....com>,
        Xiaojian Du <Xiaojian.Du@....com>,
        Viresh Kumar <viresh.kumar@...aro.org>,
        Borislav Petkov <bp@...en8.de>
Subject: Re: [PATCH V5 3/7] cpufreq: amd-pstate: Enable amd-pstate preferred
 core supporting.

On Tue, Sep 05, 2023 at 09:51:12AM +0800, Meng Li wrote:

> +static void amd_pstate_init_prefcore(void)
> +{
> +	int cpu, ret;
> +	u64 highest_perf;
> +
> +	if (!prefcore)
> +		return;
> +
> +	for_each_online_cpu(cpu) {
> +		ret = amd_pstate_get_highest_perf(cpu, &highest_perf);
> +		if (ret)
> +			break;
> +
> +		sched_set_itmt_core_prio(highest_perf, cpu);
> +
> +		/* check if CPPC preferred core feature is enabled*/
> +		if (highest_perf == AMD_PSTATE_MAX_CPPC_PERF) {
> +			hw_prefcore = false;
> +			prefcore = false;
> +			return;
> +		}
> +	}
> +
> +	/*
> +	 * This code can be run during CPU online under the
> +	 * CPU hotplug locks, so sched_set_amd_prefcore_support()
> +	 * cannot be called from here.  Queue up a work item
> +	 * to invoke it.
> +	 */
> +	schedule_work(&sched_prefcore_work);
> +}

> @@ -1506,6 +1593,8 @@ static int __init amd_pstate_init(void)
>  		}
>  	}
>  
> +	amd_pstate_init_prefcore();
> +
>  	return ret;
>  
>  global_attr_free:


I'm confused,...  you call amd_pstate_init_prefcore() at
device_initcall(). Once per boot.

Then it iterates all online CPUs..

But what if you boot with some CPUs offline and bring then online later?