Re: [PATCH V5 5/7] cpufreq: amd-pstate: Update amd-pstate preferred core ranking dynamically

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>, Wyes Karny <wyes.karny@amd.com>
Subject: Re: [PATCH V5 5/7] cpufreq: amd-pstate: Update amd-pstate preferred core ranking dynamically
Date: Fri, 8 Sep 2023 15:27:54 +0200	[thread overview]
Message-ID: <20230908132754.GI19320@noisy.programming.kicks-ass.net> (raw)
In-Reply-To: <20230905015116.2268926-6-li.meng@amd.com>

On Tue, Sep 05, 2023 at 09:51:14AM +0800, Meng Li wrote:

> +static void amd_pstate_update_highest_perf(unsigned int cpu)
> +{
> +	struct cpufreq_policy *policy;
> +	struct amd_cpudata *cpudata;
> +	u32 prev_high = 0, cur_high = 0;
> +	u64 highest_perf;
> +	int ret;
> +
> +	if (!prefcore)
> +		return;
> +
> +	ret = amd_pstate_get_highest_perf(cpu, &highest_perf);
> +	if (ret)
> +		return;
> +
> +	policy = cpufreq_cpu_get(cpu);
> +	cpudata = policy->driver_data;
> +	cur_high = highest_perf;
> +	prev_high = READ_ONCE(cpudata->cppc_highest_perf);
> +
> +	if (prev_high != cur_high) {
> +		WRITE_ONCE(cpudata->cppc_highest_perf, cur_high);
> +		sched_set_itmt_core_prio(cur_high, cpu);

I just noticed, your cur_high is explicitly 'u32', but
sched_set_itmt_core_prio() and the rest of the scheduler use 'int' (aka
s32). If you somehow get that top bit set things might not work out as
expected.

Please double check.

> +	}
> +
> +	cpufreq_cpu_put(policy);
> +}