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Shenoy" , Perry Yuan Cc: "open list:X86 ARCHITECTURE (32-BIT AND 64-BIT)" , "open list:CPU FREQUENCY SCALING FRAMEWORK" , Mario Limonciello References: <20250206215659.3350066-1-superm1@kernel.org> <20250206215659.3350066-4-superm1@kernel.org> <5577e2ad-6cd0-4fe8-a8e8-28199491ca3a@amd.com> <9b38a679-875c-436a-9383-8b0d8a1b67af@kernel.org> Content-Language: en-US From: Dhananjay Ugwekar In-Reply-To: <9b38a679-875c-436a-9383-8b0d8a1b67af@kernel.org> Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit X-ClientProxiedBy: PN3PR01CA0013.INDPRD01.PROD.OUTLOOK.COM (2603:1096:c01:95::9) To LV8PR12MB9207.namprd12.prod.outlook.com (2603:10b6:408:187::15) Precedence: bulk X-Mailing-List: linux-pm@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 X-MS-PublicTrafficType: Email X-MS-TrafficTypeDiagnostic: LV8PR12MB9207:EE_|IA0PR12MB8840:EE_ X-MS-Office365-Filtering-Correlation-Id: efc803ff-838c-4571-287a-08dd4b2ee23a X-MS-Exchange-SenderADCheck: 1 X-MS-Exchange-AntiSpam-Relay: 0 X-Microsoft-Antispam: BCL:0;ARA:13230040|1800799024|376014|366016; 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>>> -    struct amd_cpudata *cpudata = policy->driver_data; >>> +    struct amd_cpudata *cpudata; >>> +    union perf_cached perf; >>>       u8 des_perf; >>>         amd_pstate_update_min_max_limit(policy); >>>   +    cpudata = policy->driver_data; >> >> Any specific reason why we moved this dereferencing after amd_pstate_update_min_max_limit() ? > > Closer to the first use. > >> >>> +    perf = READ_ONCE(cpudata->perf); >>> + >>>       freqs.old = policy->cur; >>>       freqs.new = target_freq; >>>   -    des_perf = freq_to_perf(cpudata, target_freq); >>> +    des_perf = freq_to_perf(perf, cpudata->nominal_freq, target_freq); >> >> Personally I preferred the earlier 2 argument format for the helper functions, as the helper >> function handled the common dereferencing part, (i.e. cpudata->perf and cpudata->nominal_freq) > > Something like this? > > static inline u8 freq_to_perf(struct amd_cpudata *cpudata, unsigned int freq_val) > { >     union perf_cached perf = READ_ONCE(cpudata->perf); >     u8 perf_val = DIV_ROUND_UP_ULL((u64)freq_val * perf.nominal_perf, cpudata->nominal_freq); > >     return clamp_t(u8, perf_val, perf.lowest_perf, perf.highest_perf); > } > > As an example in practice of what that turns into with inline code it should be: > > static void amd_pstate_update_min_max_limit(struct cpufreq_policy *policy) > { >     struct amd_cpudata *cpudata = policy->driver_data; >     union perf_cached perf = READ_ONCE(cpudata->perf); >     union perf_cached perf2 = READ_ONCE(cpudata->perf); >     union perf_cached perf3 = READ_ONCE(cpudata->perf); >     u8 val1 = DIV_ROUND_UP_ULL((u64)policy->max * perf2.nominal_perf, cpudata->nominal_freq); >     u8 val2 = DIV_ROUND_UP_ULL((u64)policy->min * perf2.nominal_perf, cpudata->nominal_freq); > >     perf.max_limit_perf = clamp_t(u8, val1, perf2.lowest_perf, perf2.highest_perf); >     perf.min_limit_perf = clamp_t(u8, val2, perf3.lowest_perf, perf3.highest_perf); > . > . > . > > So now that's 3 reads for cpudata->perf in every use. Yea, right, its a tradeoff, in clean looking code vs less computations. I'll leave it upto you, I'm okay either way.