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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> <20250206215659.3350066-5-superm1@kernel.org> Content-Language: en-US From: Dhananjay Ugwekar In-Reply-To: Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit X-ClientProxiedBy: PN3PR01CA0083.INDPRD01.PROD.OUTLOOK.COM (2603:1096:c01:9a::14) 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_|PH0PR12MB7959:EE_ X-MS-Office365-Filtering-Correlation-Id: 799e4e1a-4f2d-43e7-8406-08dd4b243da3 X-MS-Exchange-SenderADCheck: 1 X-MS-Exchange-AntiSpam-Relay: 0 X-Microsoft-Antispam: BCL:0;ARA:13230040|376014|1800799024|366016; X-Microsoft-Antispam-Message-Info: =?utf-8?B?UnhZNm5YVGxTNkJmaXdZNU9RSVprVmVFNzVDYXhBZ0oyZTU1Q1VGVHVOUDVE?= =?utf-8?B?NEtiMHhVNEh3akZMdEFlWmY0UmovdkVnNzVIczBhK1lHVXBCazZVSXB4aGtR?= =?utf-8?B?WVQzRWVXTkg5RGZKeVpUTEN3R0o2WURYQko3Vm1UY3dKN0RsL05BaitEY2FD?= =?utf-8?B?bmNyZVpwSG1zN3dSbm40SVB3QUJxZGZMZGRhUWp1dGdjU3hrVktVYzRURlhF?= =?utf-8?B?NERHZys3MndiK1V2ZnBQNlhhTENzeGpVNUJpMHU5L1lwVnNmZ3NzQVVTaDB4?= =?utf-8?B?aS9UWlJNS3Jic1JWbmNuNzN1MHI5Q1drZktsNDR2b2wxQWE5dkhsQmVnZ0tq?= =?utf-8?B?c3NCM0NXYm5KOE5RNC9DOWpVRUNQYnZkVTRGRFFpT2NwbVZqWWhNUXNER1JE?= =?utf-8?B?c3BBTWM2SnJrQUpqUmtVbGdjVGJNZWlNdXZDY2RoT0F5eGcyNkpHcFFxeWlF?= =?utf-8?B?K3RzOUV2blkrNjkvdFVraUpHL3UxZ3RpdU9OUWUvSlBFNVJzWTNmdEhnS0xo?= =?utf-8?B?c1FwWEpTQ2YzK1ZJc0lQSmMyRTlTZk55cXZyMTFIUnNXRy91YUFvVlFnendY?= =?utf-8?B?RkpkbGVweEgyamFZNDhvanFscTdQOUxvVWlIZlZZQ0xkMWdGcU9LLzgvcnYr?= =?utf-8?B?aGZnUHQwTkhONklCcGo0djR3d1laM2plYlg2Nit3MkpwYWJraW15Z1M5RkxO?= =?utf-8?B?Q2lGK0NueWlzOVc5VnVPWW52TlNoZnlrR096UzJuaGlEWmJReEFGallCMHNN?= =?utf-8?B?eTRMZWFIMEZiMTNKZVRaWFhKY0VYRVphWkNLL3lMeXBSYnFNcEJwQWQxeHkr?= =?utf-8?B?U1FkNk9Ucm9zaE54SkdCM2dPMmE4QnZwd29ZdDdQaWxxTCtTMFAwaTFsOExu?= =?utf-8?B?VEZPWTZsUHhaYXFodTUvaDlLNjRUaFUra2Y1K0FYaGtyZXRMSVYwcTZVeHlJ?= =?utf-8?B?Y0ZrWDdodmlqa2pxc0N2OVRIVERYVjZBWlVtNUR0R3Q5VUZMRENmQnhqaEFt?= =?utf-8?B?czBNcnJrdjlXakN4K0U3VFozRFpqRE55dDVaeWhlalQ4TUJSdmc0NkwrdklK?= =?utf-8?B?NUJUY1duMHFoN1Y1Nm0yc1lxRnVRRmVzZ2l2M3d2VVV4cXdmc1lBK1RzalE1?= =?utf-8?B?cW15dFVYMnl0dE9ia1huUGd3cnA1TjhMcFNjZkhqSW9CQXNtSy9QNVQzaVQw?= =?utf-8?B?YkZVekNNa3JrcTUyZEdvcE9YUy85RmVXRThxU0p6QTN0cjJoMVB0NDdEdld1?= =?utf-8?B?RUZxbjltVjBpTGl4Z2VWalpSSWY4S3ZWWFNkcSthSWtMWG5LaWJtR3hOdm1F?= =?utf-8?B?d253T1BVUkVPSjN3YTYzR2tBeDVzTy94bEQzQzRVbzUralk4OVlhYXBhVG16?= =?utf-8?B?V3JtcHhFcDhWcnUvWnNvSUF0bXpFVkFPTW00RW1YQ3d3WEVrSlQ0SVV3ZFRq?= =?utf-8?B?b1IzUE8wUE5jdXltRk5aU2RjdG1OOWQ5UUhQaHAzMkNLYzFYeTd3a0p1MjJv?= =?utf-8?B?TU9xcHlDTU95NHc2Um1welN1cDl0WTVlSHFZM0htaE5FZGE0SS9OblJCWksr?= =?utf-8?B?UUwzZ2YzU1RsT3czRUVJQ09YaEhQZzI3MWVLQkVlRjVJampaVy9HU1VUWU1u?= =?utf-8?B?bjd1QnMvUnFqb2haSDB5cTN0ZHZ5S3hkeGw0TUdidnlCaVV0ZjBMU0NkL2Jh?= =?utf-8?B?b1l6bUcwYUxSeXBUcUdhbmpJdmhXT0ppQk1jQyswb1VIVTVBekFnaWNERVFw?= =?utf-8?B?c2JGRDc4a0cyLzU1Z2FVWkpHeVViTmNhWDczakFad0xMYWg3Q0xwRXVXSlFB?= =?utf-8?B?bk5DenRvM1drRkI1WGNTMENpNUFmd0JzMUpEWW9jbmVwcTVCTSs3bUc3RVpG?= =?utf-8?Q?asTwUpQv7CLjp?= X-Forefront-Antispam-Report: CIP:255.255.255.255;CTRY:;LANG:en;SCL:1;SRV:;IPV:NLI;SFV:NSPM;H:LV8PR12MB9207.namprd12.prod.outlook.com;PTR:;CAT:NONE;SFS:(13230040)(376014)(1800799024)(366016);DIR:OUT;SFP:1101; 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>>>   } >>>   -static DEFINE_MUTEX(amd_pstate_limits_lock); >>>   static DEFINE_MUTEX(amd_pstate_driver_lock); >>>     static u8 msr_get_epp(struct amd_cpudata *cpudata) >>> @@ -283,6 +282,8 @@ static int msr_set_epp(struct amd_cpudata *cpudata, u8 epp) >>>       u64 value, prev; >>>       int ret; >>>   +    lockdep_assert_held(&cpudata->lock); >> >> After making the perf_cached variable writes atomic, do we still need a cpudata->lock ? > > My concern was specifically that userspace could interact with multiple sysfs files that influence the atomic perf variable (and the HW) at the same time.  So you would not have a deterministic behavior if they raced.  But if you take the mutex on all the paths that this could happen it will be a FIFO. I guess, the lock still wont guarantee the ordering right? It will just ensure that one thread executes that code path for a specific CPU at a time. And do we even care about the ordering ? I'm having a hard time thinking of a scenario where we'll need the lock. Can you or Gautham think of any such scenario? > >> >> Regards, >> Dhananjay >> >>> + >>>       value = prev = READ_ONCE(cpudata->cppc_req_cached); >>>       value &= ~AMD_CPPC_EPP_PERF_MASK; >>>       value |= FIELD_PREP(AMD_CPPC_EPP_PERF_MASK, epp); >>> @@ -315,6 +316,8 @@ static int shmem_set_epp(struct amd_cpudata *cpudata, u8 epp) >>>       int ret; >>>       struct cppc_perf_ctrls perf_ctrls; >>>   +    lockdep_assert_held(&cpudata->lock); >>> + >>>       if (epp == cpudata->epp_cached) >>>           return 0; >>>   @@ -335,6 +338,8 @@ static int amd_pstate_set_energy_pref_index(struct cpufreq_policy *policy, >>>       struct amd_cpudata *cpudata = policy->driver_data; >>>       u8 epp; >>>   +    guard(mutex)(&cpudata->lock); >>> + >>>       if (!pref_index) >>>           epp = cpudata->epp_default; >>>       else >>> @@ -750,7 +755,6 @@ static int amd_pstate_set_boost(struct cpufreq_policy *policy, int state) >>>           pr_err("Boost mode is not supported by this processor or SBIOS\n"); >>>           return -EOPNOTSUPP; >>>       } >>> -    guard(mutex)(&amd_pstate_driver_lock); >>>         ret = amd_pstate_cpu_boost_update(policy, state); >>>       refresh_frequency_limits(policy); >>> @@ -973,6 +977,9 @@ static int amd_pstate_cpu_init(struct cpufreq_policy *policy) >>>         cpudata->cpu = policy->cpu; >>>   +    mutex_init(&cpudata->lock); >>> +    guard(mutex)(&cpudata->lock); >>> + >>>       ret = amd_pstate_init_perf(cpudata); >>>       if (ret) >>>           goto free_cpudata1; >>> @@ -1179,8 +1186,6 @@ static ssize_t store_energy_performance_preference( >>>       if (ret < 0) >>>           return -EINVAL; >>>   -    guard(mutex)(&amd_pstate_limits_lock); >>> - >>>       ret = amd_pstate_set_energy_pref_index(policy, ret); >>>         return ret ? ret : count; >>> @@ -1353,8 +1358,10 @@ int amd_pstate_update_status(const char *buf, size_t size) >>>       if (mode_idx < 0 || mode_idx >= AMD_PSTATE_MAX) >>>           return -EINVAL; >>>   -    if (mode_state_machine[cppc_state][mode_idx]) >>> +    if (mode_state_machine[cppc_state][mode_idx]) { >>> +        guard(mutex)(&amd_pstate_driver_lock); >>>           return mode_state_machine[cppc_state][mode_idx](mode_idx); >>> +    } >>>         return 0; >>>   } >>> @@ -1375,7 +1382,6 @@ static ssize_t status_store(struct device *a, struct device_attribute *b, >>>       char *p = memchr(buf, '\n', count); >>>       int ret; >>>   -    guard(mutex)(&amd_pstate_driver_lock); >>>       ret = amd_pstate_update_status(buf, p ? p - buf : count); >>>         return ret < 0 ? ret : count; >>> @@ -1472,6 +1478,9 @@ static int amd_pstate_epp_cpu_init(struct cpufreq_policy *policy) >>>         cpudata->cpu = policy->cpu; >>>   +    mutex_init(&cpudata->lock); >>> +    guard(mutex)(&cpudata->lock); >>> + >>>       ret = amd_pstate_init_perf(cpudata); >>>       if (ret) >>>           goto free_cpudata1; >>> @@ -1558,6 +1567,8 @@ static int amd_pstate_epp_update_limit(struct cpufreq_policy *policy) >>>       union perf_cached perf; >>>       u8 epp; >>>   +    guard(mutex)(&cpudata->lock); >>> + >>>       amd_pstate_update_min_max_limit(policy); >>>         if (cpudata->policy == CPUFREQ_POLICY_PERFORMANCE) >>> @@ -1646,8 +1657,6 @@ static int amd_pstate_epp_cpu_offline(struct cpufreq_policy *policy) >>>       if (cpudata->suspended) >>>           return 0; >>>   -    guard(mutex)(&amd_pstate_limits_lock); >>> - >>>       if (trace_amd_pstate_epp_perf_enabled()) { >>>           trace_amd_pstate_epp_perf(cpudata->cpu, perf.highest_perf, >>>                         AMD_CPPC_EPP_BALANCE_POWERSAVE, >>> @@ -1684,8 +1693,6 @@ static int amd_pstate_epp_resume(struct cpufreq_policy *policy) >>>       struct amd_cpudata *cpudata = policy->driver_data; >>>         if (cpudata->suspended) { >>> -        guard(mutex)(&amd_pstate_limits_lock); >>> - >>>           /* enable amd pstate from suspend state*/ >>>           amd_pstate_epp_reenable(policy); >>>   diff --git a/drivers/cpufreq/amd-pstate.h b/drivers/cpufreq/amd-pstate.h >>> index a140704b97430..6d776c3e5712a 100644 >>> --- a/drivers/cpufreq/amd-pstate.h >>> +++ b/drivers/cpufreq/amd-pstate.h >>> @@ -96,6 +96,8 @@ struct amd_cpudata { >>>       bool    boost_supported; >>>       bool    hw_prefcore; >>>   +    struct mutex    lock; >>> + >>>       /* EPP feature related attributes*/ >>>       u8    epp_cached; >>>       u32    policy; >> >