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Mon, 23 Dec 2024 23:41:58 +0000 Message-ID: <369605f0-9d6c-4a5c-bfc0-f480b537f34d@intel.com> Date: Mon, 23 Dec 2024 15:41:54 -0800 User-Agent: Mozilla Thunderbird Subject: Re: [RFC PATCH 03/15] x86/cpu/intel: Fix init_intel() checks for extended family numbers To: 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 . Peter Anvin" , "Rafael J . Wysocki" , Len Brown , Andy Lutomirski , Viresh Kumar , Fenghua Yu , Jean Delvare , Guenter Roeck , Zhang Rui , , , , , References: <20241220213711.1892696-1-sohil.mehta@intel.com> <20241220213711.1892696-4-sohil.mehta@intel.com> <54df5b3f-8b98-42b8-b3ec-3860abd5ce67@intel.com> Content-Language: en-US From: Sohil Mehta In-Reply-To: <54df5b3f-8b98-42b8-b3ec-3860abd5ce67@intel.com> Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: 7bit X-ClientProxiedBy: MW4PR04CA0079.namprd04.prod.outlook.com (2603:10b6:303:6b::24) To BYAPR11MB3320.namprd11.prod.outlook.com (2603:10b6:a03:18::25) Precedence: bulk X-Mailing-List: linux-hwmon@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 X-MS-PublicTrafficType: Email X-MS-TrafficTypeDiagnostic: BYAPR11MB3320:EE_|MW3PR11MB4522:EE_ X-MS-Office365-Filtering-Correlation-Id: 04a394db-bdfe-42d6-f568-08dd23ab63dd X-LD-Processed: 46c98d88-e344-4ed4-8496-4ed7712e255d,ExtAddr X-MS-Exchange-SenderADCheck: 1 X-MS-Exchange-AntiSpam-Relay: 0 X-Microsoft-Antispam: BCL:0;ARA:13230040|7416014|376014|1800799024|366016; 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Extend the >> check to family numbers beyond 15. > > Could you explain why, please? > To answer this I was trying to understand where Fast string (X86_FEATURE_REP_GOOD) is used. It looks like copy_page() in lib/copy_page_64.S is the only place it really matters. clear_page() in include/asm/page_64.h would likely use Enhanced fast strings (ERMS) if available. Would it be correct to say that copy_page() and potentially clear_page() would be slower on Family 18/19 CPUs without the fix? >> It is uncertain whether the Pentium 4s (family 15) should set the >> feature flag as well. Commit 185f3b9da24c ("x86: make intel.c have >> 64-bit support code") that originally set X86_FEATURE_REP_GOOD also set >> the x86_cache_alignment preference for family 15 processors. The >> omission of the family 15 seems intentional. >> Analyzing more, it seems the below check in early_init_intel() is not really effective. /* * 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)) { pr_info("Disabled fast string operations\n"); setup_clear_cpu_cap(X86_FEATURE_REP_GOOD); setup_clear_cpu_cap(X86_FEATURE_ERMS); } } It gets overridden later in intel_init() with the below code: if (c->x86 == 6) set_cpu_cap(c, X86_FEATURE_REP_GOOD); Shouldn't the order of this be the other way around? >> Also, the 32-bit user copy alignment preference is only set for family 6 >> and 15 processors. Extend the preference to family numbers beyond 15. > > Can you please provide some more context so it's clear which hunk this > refers to? Alternatively, can you break this out into a separate patch? > This is referring to the below chunk. Separating it seems like a better idea to avoid ambiguity. > - > #ifdef CONFIG_X86_INTEL_USERCOPY > /* > * Set up the preferred alignment for movsl bulk memory moves > + * Family 4 - 486: untested > + * Family 5 - Pentium: untested > + * Family 6 - PII/PIII only like movsl with 8-byte alignment > + * Family 15 - P4 is OK down to 8-byte alignment > */ > - switch (c->x86) { > - case 4: /* 486: untested */ > - break; > - case 5: /* Old Pentia: untested */ > - break; > - case 6: /* PII/PIII only like movsl with 8-byte alignment */ > - movsl_mask.mask = 7; > - break; > - case 15: /* P4 is OK down to 8-byte alignment */ > + if (c->x86_vfm >= INTEL_PENTIUM_PRO) > movsl_mask.mask = 7; > - break; > - } > #endif