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

From: Peter Zijlstra <peterz@infradead.org>
To: Meng Li <li.meng@amd.com>
Cc: "Rafael J . Wysocki" <rafael.j.wysocki@intel.com>,
	Huang Rui <ray.huang@amd.com>,
	linux-pm@vger.kernel.org, linux-kernel@vger.kernel.org,
	x86@kernel.org, linux-acpi@vger.kernel.org,
	Shuah Khan <skhan@linuxfoundation.org>,
	linux-kselftest@vger.kernel.org,
	Nathan Fontenot <nathan.fontenot@amd.com>,
	Deepak Sharma <deepak.sharma@amd.com>,
	Alex Deucher <alexander.deucher@amd.com>,
	Mario Limonciello <mario.limonciello@amd.com>,
	Shimmer Huang <shimmer.huang@amd.com>,
	Perry Yuan <Perry.Yuan@amd.com>,
	Xiaojian Du <Xiaojian.Du@amd.com>,
	Viresh Kumar <viresh.kumar@linaro.org>,
	Borislav Petkov <bp@alien8.de>
Subject: Re: [PATCH V5 3/7] cpufreq: amd-pstate: Enable amd-pstate preferred core supporting.
Date: Fri, 8 Sep 2023 15:17:02 +0200	[thread overview]
Message-ID: <20230908131702.GF19320@noisy.programming.kicks-ass.net> (raw)
In-Reply-To: <20230905015116.2268926-4-li.meng@amd.com>

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?