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: <0ec93276-e97a-0a66-fe86-4f355cf1d411@amd.com>
Date:   Wed, 19 Jul 2023 13:07:59 +0530
User-Agent: Mozilla Thunderbird
Subject: Re: [PATCH 3/6] x86/cpuid: Add smp helper
Content-Language: en-US
To:     Peter Zijlstra <peterz@infradead.org>
Cc:     linux-kernel@vger.kernel.org, linux-perf-users@vger.kernel.org,
        x86@kernel.org, mingo@redhat.com, acme@kernel.org,
        mark.rutland@arm.com, alexander.shishkin@linux.intel.com,
        jolsa@kernel.org, namhyung@kernel.org, irogers@google.com,
        adrian.hunter@intel.com, tglx@linutronix.de, bp@alien8.de,
        dave.hansen@linux.intel.com, hpa@zytor.com, eranian@google.com,
        ananth.narayan@amd.com, ravi.bangoria@amd.com,
        santosh.shukla@amd.com
References: <cover.1689748843.git.sandipan.das@amd.com>
 <827723d8f506411700c68bccc5072ec8d918d2de.1689748843.git.sandipan.das@amd.com>
 <20230719072850.GA3529734@hirez.programming.kicks-ass.net>
From:   Sandipan Das <sandipan.das@amd.com>
In-Reply-To: <20230719072850.GA3529734@hirez.programming.kicks-ass.net>
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?bXpDYWNORXZBK2pxWG4ycGw0K2xWQk50RENBS1RtcnZNSEtEKzdTbk1CenZC?=
 =?utf-8?B?QUgxQUh2ZGNyQm13YlpWWTN3a2FQS21LTkpoblRRTGhJOUFkWVJoVHZOckla?=
 =?utf-8?B?WDJYRDdPaFc5V3RtV3ZYUllneXlnVDYwaU5jM0o1L0RDYjNiMkZaLzZQQjFs?=
 =?utf-8?B?ZnkzNk1Wc3pKYUNjRzZrZ0xhZElucjBjWVIzb21RcDRxenJsaTNFcHJHbmx4?=
 =?utf-8?B?SVdrOEJSWm9tNkpZYlNFTFJETzdKbDlYK2NtR3d5WG5XbDJlVlFQbnpTakVv?=
 =?utf-8?B?NCtzbDNzL1VtTDBKNDlqYjhJMXlTRG5tdDR4UU56V2luenFQZmZ0UU5XRGtM?=
 =?utf-8?B?eGdiZlkvelMyTTlidy9KbmRWYll1Zm1kYUNTMGZaMVJoYXFkTFhQSGZLd0s0?=
 =?utf-8?B?SmlDQWRENkRmVWRnQlorZUp5RHBTZXVYTTRqWDNQd1h5cmRKZldvdzVxUlBx?=
 =?utf-8?B?RXA4ZS8yWXkzS0pTdURnN3EvdEhvN1VPbW5ocm9OY3p5Q1M0VERLNW1KYWdm?=
 =?utf-8?B?WU1aUjhCTjJlODZ6YlVscUZoQ1hZNFNLaWpCeUY3aU9KditFckZHNFU5azBV?=
 =?utf-8?B?MXJ1U3dORy90T0VPanViNDRxOEFNbUZ6Q2xzSVFlMDNickFIZGgwcDMxd3Y2?=
 =?utf-8?B?ZFVaVkV5bzBJNnB2YWJWaThMS3lKUjBhVTRJM243TFlEd284K1RJRHdqanFP?=
 =?utf-8?B?YWNmNHIyU0I5SENGNGVQQUx4eVlqa2VUZEQ0bEl5V0VTeGcxM2tsRUxnN2FF?=
 =?utf-8?B?NEY1Rzg4bUxnL1R2a20zSFFsdkV2K2w5NCtuVk5XWEQ4RHhjSmswM21pVnVa?=
 =?utf-8?B?b2dHYU4wanF6eXV4TFRoMWY2OTFnc3R2Mm1ENnd3QlhUZmVBaVFrd0ZVL25q?=
 =?utf-8?B?a2FRNXRFUHdrbGcyVGwzNXF2azlkN1FpZU9lT2Y0MzVmdnVKcmoxNEpLZ1lD?=
 =?utf-8?B?dVh0TXNJcExrejRtQjhSMWJHcXVQWkhnaEtsWEtaL2JtbDljVEVHeW14Zy9l?=
 =?utf-8?B?NVM1bi81ckc2MXIzMGNiN2hna3U5NGVMaTFzSExURG9QWVJ3Wm12VDVOc3dk?=
 =?utf-8?B?V29ENnBNT1N1dUdoWUh3TXJHaWoremFVYzRqQmNiaWU3NHVtYlE0SjR0Z2cv?=
 =?utf-8?B?WmE1OXI3NWh5SVlsQnhhbzNmRXdheGtoTW5GSjNPWk94TWVzbVI3b1JBMmZk?=
 =?utf-8?B?cjBJRjdlWHFZcWZvTUFMMFltN3l3bHl4WkQwYVQxZWhDd3g1VExMbDg4aG0y?=
 =?utf-8?B?K0k5WXhCWkk3WHF0R2FHY1hHRGlndW9pTlpTNlpFMUFWZWRFSEtEN1B0SGNv?=
 =?utf-8?B?S3lCZUJZMVE4TmlsekFXOTRxeVp1NkZFOTBXQ3dkS2xMcFdmVTMyZDJLSXZ3?=
 =?utf-8?B?cVhjaS9ERUZQeVI1bW5pRkIwWlNueWxja3NkK2ZEVkExcjF3NXpuYjhTQ3dB?=
 =?utf-8?B?dnhTNXJYc09iZ1Q1alNrdXVNWFZDdUVIcnBEVHY1Rk9PSzBoVW1IWmJ5a0hu?=
 =?utf-8?B?SXJlS3pnTUZiTzVDemZpN1BJanY2ZzBPbkFsT3Z1elg2dXJlOTU5aENPT2s0?=
 =?utf-8?B?MXRtSStBczROcW5NSGN5Y2k1L0dIdnVNdjZYeDhGR2J0YXJ2MysrSlduQXF1?=
 =?utf-8?B?RExJMGQ5YWRxTTJlYWVvaDU3dG5rWlRKclVZWEF5VEpYZ0lFUmtWUzlmSEFL?=
 =?utf-8?B?NFRTTTEvQ2lXNHVQL2RiVUZ5TGh5NUs4ZkVnMVZLcU5hUTBhWm9jdDdzckUx?=
 =?utf-8?B?NWg0QzRSaXRZZUJ0TWd3SU5aZnhxTVRpbkxkV1JWd3doRTk0bDAyZFdVUUh1?=
 =?utf-8?B?NzhEb1ViQjlKa2JFZU1zL1JiNTBoREJPdGYwYzFjeFoweDdoSzlVRS9RMGtv?=
 =?utf-8?B?U2h1Z2NiL2ZsamtnZ2R0dGFWV2M3bmJGSFk2cjhUZDlGVTlJd3pDemcvaVl0?=
 =?utf-8?B?SWt4Wllsb2pwZ2tOVGhBMy93VFRQdDdOUUtSYXRobjVOeE9uYVlmUkJUZ2Fv?=
 =?utf-8?B?dG03YUdoeDlrbDIxUjNGV3ZlZi8zbng2d05jcXF1dkkwbkF6c2JoTW9iK1FE?=
 =?utf-8?B?UnYxOUt0QmhockxlTzhYNnJEZ2MrNCszOERMY2tZRU5vK2w3dm5ldEg2K3Bt?=
 =?utf-8?Q?DWdvU26GHmP4RhWk11f+T+nxg?=
X-OriginatorOrg: amd.com
X-MS-Exchange-CrossTenant-Network-Message-Id: 0e719ed0-c505-4498-d054-08db882b17a8
X-MS-Exchange-CrossTenant-AuthSource: PH7PR12MB5712.namprd12.prod.outlook.com
X-MS-Exchange-CrossTenant-AuthAs: Internal
X-MS-Exchange-CrossTenant-OriginalArrivalTime: 19 Jul 2023 07:38:26.0459
 (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: IQK11iDOL+MFDXLhRfdsP+FaQzOpSTSgfgUepvbl7Ah2dMSArbBM9NQdRItcigb/x9Ncyh5SXAw1z7753KhVCg==
X-MS-Exchange-Transport-CrossTenantHeadersStamped: PH7PR12MB7018
X-Spam-Status: No, score=-1.1 required=5.0 tests=BAYES_00,DKIM_SIGNED,
        DKIM_VALID,DKIM_VALID_AU,DKIM_VALID_EF,FORGED_SPF_HELO,
        RCVD_IN_DNSWL_BLOCKED,RCVD_IN_MSPIKE_H2,SPF_HELO_PASS,SPF_NONE,
        T_SCC_BODY_TEXT_LINE,URIBL_BLOCKED autolearn=no 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 7/19/2023 12:58 PM, Peter Zijlstra wrote:
> On Wed, Jul 19, 2023 at 12:25:38PM +0530, Sandipan Das wrote:
>> Depending on which CPU the CPUID instruction is executed, some leaves
>> can report different values. There are cases where it may be required
>> to know all possible values.
>>
>> E.g. for AMD Zen 4 processors, the ActiveUmcMask field from leaf
>> 0x80000022 ECX, which provides a way to determine the active memory
>> controllers, can have different masks on CPUs belonging to different
>> sockets as each socket can follow a different DIMM population scheme.
>> Each memory channel is assigned a memory controller (UMC) and if no
>> DIMMs are attached to a channel, the corresponding memory controller
>> is inactive. There are performance monitoring counters exclusive to
>> each memory controller which need to be represented under separate
>> PMUs. So, it will be necessary to know the active memory controllers
>> on each socket during the initialization of the UMC PMUs irrespective
>> of where the uncore driver's module init runs.
>>
>> Add a new helper that executes CPUID on a particular CPU and returns
>> the EAX, EBX, ECX and EDX values.
>>
> 
> So I hate all this for multiple reasons:
> 
>  - the wohle foo_on_cpu() model generally leads to atrocious code that
>    does multiple IPIs, I've seen rdmsr_on_cpu() followed by
>    wrmsr_on_cpu() and worse things, just don't do this.
> 
>  - The whole CPUID thing is insane; we should read CPUID -- all of it --
>    *ONCE* at bringup and thereafter never touch the instruction ever
>    again. It could be people are already working on patches to this
>    effect.
> 
>  - Different CPUID values for different CPUs is a pain :/

Thanks for the clarification. Will remove this.

- Sandipan