Received-SPF: pass (google.com: domain of linux-kernel-owner@vger.kernel.org designates 2620:137:e000::1:20 as permitted sender) client-ip=2620:137:e000::1:20;
Message-ID: <dfc687f8-3c3f-f866-7e6c-8fcb68e0cd89@amd.com>
Date:   Fri, 23 Sep 2022 17:17:35 +0530
User-Agent: Mozilla/5.0 (Windows NT 10.0; Win64; x64; rv:91.0) Gecko/20100101
 Thunderbird/91.11.0
From:   Ananth Narayan <ananth.narayan@amd.com>
Subject: Re: [PATCH] ACPI: processor_idle: Skip dummy wait for processors
 based on the Zen microarchitecture
To:     "Limonciello, Mario" <Mario.Limonciello@amd.com>,
        Dave Hansen <dave.hansen@intel.com>,
        "Nayak, K Prateek" <KPrateek.Nayak@amd.com>,
        "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>
Cc:     "rafael@kernel.org" <rafael@kernel.org>,
        "lenb@kernel.org" <lenb@kernel.org>,
        "linux-acpi@vger.kernel.org" <linux-acpi@vger.kernel.org>,
        "linux-pm@vger.kernel.org" <linux-pm@vger.kernel.org>,
        "dave.hansen@linux.intel.com" <dave.hansen@linux.intel.com>,
        "bp@alien8.de" <bp@alien8.de>,
        "tglx@linutronix.de" <tglx@linutronix.de>,
        "andi@lisas.de" <andi@lisas.de>, "puwen@hygon.cn" <puwen@hygon.cn>,
        "peterz@infradead.org" <peterz@infradead.org>,
        "rui.zhang@intel.com" <rui.zhang@intel.com>,
        "gpiccoli@igalia.com" <gpiccoli@igalia.com>,
        "daniel.lezcano@linaro.org" <daniel.lezcano@linaro.org>,
        "Shenoy, Gautham Ranjal" <gautham.shenoy@amd.com>,
        "Ong, Calvin" <Calvin.Ong@amd.com>,
        "stable@vger.kernel.org" <stable@vger.kernel.org>,
        "regressions@lists.linux.dev" <regressions@lists.linux.dev>
References: <20220921063638.2489-1-kprateek.nayak@amd.com>
 <20e78a49-25df-c83d-842e-1d624655cfd7@intel.com>
 <0885eecb-042f-3b74-2965-7d657de59953@amd.com>
 <88c17568-8694-940a-0f1f-9d345e8dcbdb@intel.com>
 <MN0PR12MB610110D90985366A4B952CCCE24E9@MN0PR12MB6101.namprd12.prod.outlook.com>
 <9d3d3424-a6d4-4076-87ff-a1c216de79c6@intel.com>
 <MN0PR12MB6101D3B6F6FF4C5BC2208FB2E24E9@MN0PR12MB6101.namprd12.prod.outlook.com>
Content-Language: en-US
In-Reply-To: <MN0PR12MB6101D3B6F6FF4C5BC2208FB2E24E9@MN0PR12MB6101.namprd12.prod.outlook.com>
Content-Type: text/plain; charset=UTF-8
Content-Transfer-Encoding: 7bit
MIME-Version: 1.0
X-MS-Exchange-AntiSpam-MessageData-ChunkCount: 1
X-MS-Exchange-AntiSpam-MessageData-0: =?utf-8?B?NmtmVFY1R0MrbFVtNENIK1Z2TFI5Z2JZd2E0d2tHY3dRVWIrcFF1UStlRS9p?=
 =?utf-8?B?MUZ2dmt4MGxqOHNUMnM2eW8wdVltdUJNZmVXQ0dYQUlYQjlJdzczT09iRDRK?=
 =?utf-8?B?THRlM250SmQ4Y0ZLdUJJN0pLcThQZzhyUlRhWE9IajAzOGg5dUVFanQ2Q0wy?=
 =?utf-8?B?V3VHTGY5RWhibzRLdUp5YWUyUk1DZjdhcVd0dG1VV0J2RlY2WVZqc0Z4RzVj?=
 =?utf-8?B?REp2OHJHaWhxdVRPR2FOTVJXWjQrOHFQQTAvT1RsQ2k5dm5PUUJUbGJnN0xm?=
 =?utf-8?B?L29UTHNmV2hqS05KN3VHdElOWHBuanZYbXhjdm1wYUpxeWJ4Q1E4SWo0bFhQ?=
 =?utf-8?B?OUdRZzZoWXNxYmtPS0paMWlxVER5Ui9QM1Q0bHdtamdKSDdpaXR3akc4QVc3?=
 =?utf-8?B?bGIrQzM5YjJkZFl6TVVlek1BSkZWeDRYVzk3ZGdndzdvcW50bFJ6VXUrREZF?=
 =?utf-8?B?Y2FGczJWeVhDVklUUXk0MFJBeGlVbHBKUlVjY21FaFlMT3VZTEJHL1N3UEJP?=
 =?utf-8?B?cnVQc1NXZkJVRGxXYVRkb1p3V2VJU2RvV1hiUS9Tdm5qV3MwRXN4dlRuY3I5?=
 =?utf-8?B?ajFlbzhHalF1a2srb2NPRlVSeitLd2N1eTlkbFRCdXZ3eE8yMkdMYWdoQS9a?=
 =?utf-8?B?dXlscVVaMDd2ZE9QUlU3VU5ZVEVibUpSYlVzT2tmSCtQUmo3dFo4V1gyS25r?=
 =?utf-8?B?RkkxV2w2bHZ6MjdZUGkxanZHMDA2M1RIejE2VGVIWXRDcjZiQzhLVDBSVUYz?=
 =?utf-8?B?SzE4eHVDOEdHR013ZEhIdjZTQVNWWUVzcTFLZGp6cGpqdVRvSTBvTklXTlNm?=
 =?utf-8?B?RDQxSmljRW9zU0Nvb2dQbmtEV3lPLzJBeFZGWU4xNVJaMlM1U0Q2S1JJQ0Z1?=
 =?utf-8?B?dDdJZUpMakNEQWVrVHp2MDRlQ1N2WEt0RUI3N0R4WDd1YmEvUkJvTWR6UHd0?=
 =?utf-8?B?RWhlNkdxWHNMdFBEamZSaHZvOGFtYnNDR1JYOUprTGgvVFBYWHB4L0Y3RW14?=
 =?utf-8?B?dWhDTXdEVW1Fb3h0bHZOZTNEdVRvTndHVTE3MFNKZStMdkt3ZnpsMjFCeWI4?=
 =?utf-8?B?UnpodWZhUWtzaTZLbUdXaVRvM0RFaHcxZ2lpNlo5UjljYkppd1MvZ0ZTYmtJ?=
 =?utf-8?B?eXRadVkzMGZhNDNXejk0YzYxamEvZEg2L2MyRm02ZXp2MXNoZm5MNWdiYlZ3?=
 =?utf-8?B?WTNYSUpGdldRSkpQS2oyQVFKeDhGenhpd0FrbDdtWWdUUTdsSVZRL1RYR2Vm?=
 =?utf-8?B?bzhHSzVQeGdpWllqRnJFYmVCS2gxVEw4VTA5ejZvckFpaHZEUEdsVDQrcG53?=
 =?utf-8?B?SkdOcUdidTlQSE82dTRkRFUxWGExazVxTzgyQkN3N2NoOUhFdHd1eUVjRnd2?=
 =?utf-8?B?SDZ4UXZ1QUJDYW9KaTl6SjBhVUdCTUhST0lLVktpVlhzVlA0M01LSkd0aHVC?=
 =?utf-8?B?dWhJNVZ5Q1lPZmNieDRmQUVlc1plQVdWWmVENkVzOFBoZjJicmtuQXd4S0wz?=
 =?utf-8?B?c2tYQVFPTGNMNFFEbVVsenVNaE1mbGw5L0dJYmczTDZUUUd0QkVXdUVLcVhx?=
 =?utf-8?B?Mzd0TjlKUWNESUtOUEhKdHJheVVvVHdDdTFJYllwaFRkZVNxNFBSMmpMeXo1?=
 =?utf-8?B?Ymk5U0Mrc25ucDFuWFY3QmJMTHgrVnJJZzBROUpNaGtQNTdIWjJLM3BMUlhr?=
 =?utf-8?B?NElzVmtCUStVTzVzNTI4U3pIdzJaMjArclplZUxzSi9CYVVuOS8vdnhteTMw?=
 =?utf-8?B?Z0JzR2tyVUJUbXNZTWRFRGhoUi84Y2M1dGV4RkFYckdWOEtZMm5JdVRMdjdP?=
 =?utf-8?B?Y0xVSXhBSXVRRFR5aTE0MThNMnUrQjNFV0ZFOUNxMmdQZUcxUmc4eE1hRzQy?=
 =?utf-8?B?UVJzZWUrMEhhUFFWM090OERFdHY3ZGFnTHZ4OWltQ1NwbGtCN0JDVDJLVVVF?=
 =?utf-8?B?dTNER0VYcGJ5WVNrdDhxaUNCY1VoVVk2U2FNMkZzQ0VkaGd3aUM5c2trZENZ?=
 =?utf-8?B?VHllNHc2a0w4RkY0eU5UTUVvWmxRK1BIZnJoWmY2QXdHUVVWVnJ0QnZQQTFr?=
 =?utf-8?B?U2NQMTQwd1pSOEpUVE51K3h0aXNuUkVpYUZkYUZuTERaejhEdm0rOVQxQW03?=
 =?utf-8?Q?YmmFdb3FWrod3bSZuk069mndX?=
X-OriginatorOrg: amd.com
X-MS-Exchange-CrossTenant-Network-Message-Id: 5c1db8ad-7996-4897-2e44-08da9d59715a
X-MS-Exchange-CrossTenant-AuthSource: CY5PR12MB6204.namprd12.prod.outlook.com
X-MS-Exchange-CrossTenant-AuthAs: Internal
X-MS-Exchange-CrossTenant-OriginalArrivalTime: 23 Sep 2022 11:47:50.9793
 (UTC)
X-MS-Exchange-CrossTenant-FromEntityHeader: Hosted
X-MS-Exchange-CrossTenant-Id: 3dd8961f-e488-4e60-8e11-a82d994e183d
X-MS-Exchange-CrossTenant-MailboxType: HOSTED
X-MS-Exchange-CrossTenant-UserPrincipalName: c1omTvrZYGof39N6Xop2S1nlg0mnKgB119fp0HiAZqk7axkH4cPqN40W89cN4RAECfnTMgsfleifyEvu9Rm1kw==
X-MS-Exchange-Transport-CrossTenantHeadersStamped: CH2PR12MB5515
X-Spam-Status: No, score=-2.1 required=5.0 tests=BAYES_00,DKIM_SIGNED,
        DKIM_VALID,DKIM_VALID_AU,DKIM_VALID_EF,NICE_REPLY_A,RCVD_IN_DNSWL_NONE,
        RCVD_IN_MSPIKE_H2,SPF_HELO_PASS,SPF_PASS autolearn=ham
        autolearn_force=no version=3.4.6
X-Spam-Checker-Version: SpamAssassin 3.4.6 (2021-04-09) on
        lindbergh.monkeyblade.net
Precedence: bulk
List-ID: <linux-kernel.vger.kernel.org>
X-Mailing-List: linux-kernel@vger.kernel.org

On 22-09-2022 11:58 pm, Limonciello, Mario wrote:
>> BTW, is there seriously a strong technical reason that AMD systems are
>> still using this code?  Or is it pure inertia?
> 
> Maybe a better question for Ananth and Prateek to comment on.

We have evaluated using MWAIT for C2 entry and feel that there are good micro
architectural reasons to stick to IOPORT based transitions for now.

Regards,
Ananth