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Wed, 12 Feb 2025 21:19:53 +0000 Message-ID: <90eb900b-0b75-4c0d-be65-a4357729e5cd@intel.com> Date: Wed, 12 Feb 2025 13:19:51 -0800 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v2 05/17] x86/cpu/intel: Fix page copy performance for extended Families To: Andrew Cooper , Dave Hansen , , Dave Hansen , Tony Luck CC: Peter Zijlstra , Ingo Molnar , Arnaldo Carvalho de Melo , Namhyung Kim , Mark Rutland , "Alexander Shishkin" , Jiri Olsa , Ian Rogers , Adrian Hunter , "Kan Liang" , Thomas Gleixner , Borislav Petkov , "H . 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X-MS-Exchange-AntiSpam-MessageData-ChunkCount: 1 X-MS-Exchange-AntiSpam-MessageData-0: =?utf-8?B?dVlFM0FXYTJpZjR5WVZ3blVwRWlXdWtnTENIZGVxTytOQ052K2VuYVJxK0cv?= =?utf-8?B?MTZCekNUclZjaGFSWi9KZkR2NlRZaWorVUROckVRREtpdEx3bTRjenhqeUVn?= =?utf-8?B?blQ0eC9zOHY0V1dYbnI0R243c29PKzM1QU44QkxFVGdCNlJVaGdZcGl6QkVN?= =?utf-8?B?VjlWTTdpWU9SMGNDWWwvdG1VMW1OR1dhZldYSHlqanFRVG9kQkkxUWFFVXc5?= =?utf-8?B?ZFM0ek1GM3NybzJiN0pZaDloeDZHTkYvUjlGRFFsbFB5a3c2STg1b2pFRk5l?= =?utf-8?B?d1VXRGtRVlhFYVpzOXFDODR0MFBjeUlQQmZiSUpnOXc4SEJxa0pnSVA3UUls?= =?utf-8?B?N0RqNzdmOUpPSHVrRTlVRjFrR0l5cE15UnZldy9FUmhNNEVMNjRnMmt2RUw0?= =?utf-8?B?WHZ0ci8yWWYzRDhTS05uSk1LN0xpL3hyZ2NPY2FGdzhtTkFyNW5QVlByNy9y?= =?utf-8?B?NjYvazdaZlVpeTU4a045QzBIL1NPaTJIbU1CaGNxdXhPcE9qZmtUc1pPaWdz?= =?utf-8?B?WFU0YkhYQ2pDREZ0dmh1M3F2dUYybTExNXpwcmVOZUF1WURiR2p6Rjc1RnhQ?= =?utf-8?B?QzNaTXh6RFdkUDcvVkEraDY3cnhpQ1BJczMzM0pDOEw1bEEyWmlzVHBPREVj?= =?utf-8?B?c2pnT1l3UjlrZHN1dURQMkhIbk4yZlRRK2xYcW91L29tSGZLR21iM1FHYzFn?= =?utf-8?B?a1B2THZqSnAvYWtqRG12YzY5SkQzZkZrRmtKbS81RFpUTTNjL285TEV5amtV?= =?utf-8?B?dUgyeXI0Q0dUemppT3Bmc05QZU13a1RpeDY4VHBYeEFCaTh4OG96ZHM3Qysr?= =?utf-8?B?Y1o0T2pzZDM5NWhCSTFZWXJ1T2ErY2JFRzRwbTk0WmNSSWNZYUpubDFRR3dM?= =?utf-8?B?OTBYWHg0WmJFL0JycFhzdWF4TUlVVzdWYUh2SkdKRjNXbDhMQlV0dXdYay9B?= =?utf-8?B?L2paSmJxbXlHbWJlRVVETVJkTWY3eFJCellqVTBoaDZNT09KbkxSODVYcFI3?= =?utf-8?B?UmFzMFFVOW9IOWg1NklmeCtKdFBqUHFvT1hKcWRmQk5SeFoxNWNadXJLS0dJ?= =?utf-8?B?MnUrWGh1ZWR0a3UvYzVMTmlTOTREUGRkblpyR1FkOXFYSldUQzg2ZmlwTUVU?= =?utf-8?B?d2NJMlJDUTlMUEdDdjZ4Q1h5SGg4ejU1b0c5R1hocXBzTjdsQUVrNVhWMXh0?= =?utf-8?B?MW80OWY1aGZmVEdtRHI5VTZNVDBqNndydm42K2VlQUFlb1RrU1ptam1LTXIz?= =?utf-8?B?RUYwNzVDUWc2aFhsSkZDME1ua0pWVzRLN20yWEs5SE9XaVdvNThMd1U5bWx2?= =?utf-8?B?MS9sR0Y2WEFRVDJvV2U2cnZ2bWZxTFRPa0VhYTAxMU5SUU5ORDBLQlNTdHov?= =?utf-8?B?c2l3V2FhSnBENlJKSmRpYXJxc3ZjSUcyUWo3NGJEWHVXVWZFS1N6WXNSQTRH?= =?utf-8?B?c2M2KzMzK2J1c2lJSzNOOGVaYWl6NDU5WmhzV2l5bHdRY2NzNHVpVk9HWlpp?= =?utf-8?B?N2VmVzRta1FwMWFiVEVoVlBGRWsxK3FyUStKREI1UGlEeGdnVURCSXhrc0tl?= =?utf-8?B?VUVHVlA0OUtOa0ZyNkZjbm1KOVBVRko2a3JuUEVyODNOTTN0TWxMZDQ3T2o2?= =?utf-8?B?bkV2YytoaTMya251NlZhbitBRnlxbmV6NVR0VEpCWUZGZ3J6TVIrTm1xb0JS?= =?utf-8?B?MzJ5ckxyWjkrODBxTnhuSkNWVGNJSUs5VmowRWZCaVBpbEVuRnF5SmlIMGVC?= =?utf-8?B?WVNsbWp5RGZyeU5STk16UHI3M3NGS0F4VWF2MFJlVGdtSjdPK2FkNzkzczU0?= =?utf-8?B?UFNJdy9zajcwbjczZnJUZkw4R016SU9qc0VnK3I0ejJGcGl5eXVNYTdXZFpw?= =?utf-8?B?Q2ZMOFVidG8wN2tOTkdwcTAvN2svTmZlVnFKT0hZc0lKTWhGZlAxbkFuck9m?= =?utf-8?B?WXJlK0NiWmtwWS9UMGdMMVdTMW01RzlRMkUzN0xBaVh5UjduRWFySHJreXYw?= =?utf-8?B?QjFKeUNGMDUwNEx6ZW5tZ200SE1QYUc2TWtUYmF0QTkzSzhOaGxZdG5pRmY4?= =?utf-8?B?ejRobzBmaGlSOUN0Um8vT3loR0sxZVJLTXdYWWJuM1BtNkRQRDFqWUxkVklQ?= =?utf-8?Q?LoYYmAy0wHy6FQmCt8M/zTe+O?= X-MS-Exchange-CrossTenant-Network-Message-Id: 1cafc9ce-5f84-4a1e-9b13-08dd4baafda6 X-MS-Exchange-CrossTenant-AuthSource: BYAPR11MB3320.namprd11.prod.outlook.com X-MS-Exchange-CrossTenant-AuthAs: Internal X-MS-Exchange-CrossTenant-OriginalArrivalTime: 12 Feb 2025 21:19:53.0079 (UTC) X-MS-Exchange-CrossTenant-FromEntityHeader: Hosted X-MS-Exchange-CrossTenant-Id: 46c98d88-e344-4ed4-8496-4ed7712e255d X-MS-Exchange-CrossTenant-MailboxType: HOSTED X-MS-Exchange-CrossTenant-UserPrincipalName: mhv0C7OO8bRJafBdFAsDcYqd+sI3AQmwEeS7n0YY/Tufq6f6nP0mdh1nhxg+ni0QdHR7nxCSPSLMKZTeVA/e5Q== X-MS-Exchange-Transport-CrossTenantHeadersStamped: PH0PR11MB4903 X-OriginatorOrg: intel.com On 2/11/2025 4:54 PM, Andrew Cooper wrote: > If you're going to override the BIOS setting, then you need to > explicitly set MSR_MISC_ENABLE.FAST_STRINGS. > > Otherwise you're claiming to Linux that REP is good even when hardware > is prohibited from using optimisations. > I think the current checks have unnecessary overlap which makes them confusing. We should be fine if we only rely on the architectural MSR_MISC_ENABLE.FAST_STRINGS bit and rely just on the BIOS setting. My justification is below. The simplified version of the current checks is as follows: Check 1 (Based on Family Model numbers): > /* > * Unconditionally set REP_GOOD on early Family 6 processors > */ > if (IS_ENABLED(CONFIG_X86_64) && > (c->x86_vfm >= INTEL_PENTIUM_PRO && c->x86_vfm < INTEL_PENTIUM_M_DOTHAN)) > set_cpu_cap(c, X86_FEATURE_REP_GOOD); This check is mostly redundant since it is targeted for 64 bit and very few if any of those CPUs support 64 bit processing. I suggest that we get rid of this check completely. The risk here is fairly limited as well. Check 2 (Based on MISC_ENABLE.FAST_STRING): > /* > * If fast string is not enabled in IA32_MISC_ENABLE for any reason, > * clear the fast string and enhanced fast string CPU capabilities. > */ > if (c->x86_vfm >= INTEL_PENTIUM_M_DOTHAN) { > rdmsrl(MSR_IA32_MISC_ENABLE, misc_enable); > if (misc_enable & MSR_IA32_MISC_ENABLE_FAST_STRING) { > /* X86_FEATURE_ERMS will be automatically set based on CPUID */ > set_cpu_cap(c, X86_FEATURE_REP_GOOD); > } else { > pr_info("Disabled fast string operations\n"); > setup_clear_cpu_cap(X86_FEATURE_REP_GOOD); > setup_clear_cpu_cap(X86_FEATURE_ERMS); > } > } This is the only real check that is needed and should likely suffice in all meaningful scenarios. Comments?