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Peter Anvin" , Arnd Bergmann , , , Qiuxu Zhuo , "Prem Nath Dey" , Xiaoping Zhou Subject: Re: [PATCH v2] x86/paravirt: Disable virt spinlock on bare metal Message-ID: References: <20240526015847.14142-1-yu.c.chen@intel.com> Content-Type: text/plain; charset="us-ascii" Content-Disposition: inline In-Reply-To: <20240526015847.14142-1-yu.c.chen@intel.com> X-ClientProxiedBy: SI2PR02CA0047.apcprd02.prod.outlook.com (2603:1096:4:196::14) To DM4PR11MB6020.namprd11.prod.outlook.com (2603:10b6:8:61::19) Precedence: bulk X-Mailing-List: virtualization@lists.linux.dev List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 X-MS-PublicTrafficType: Email X-MS-TrafficTypeDiagnostic: DM4PR11MB6020:EE_|CY8PR11MB7337:EE_ X-MS-Office365-Filtering-Correlation-Id: 0d1958f8-eeb0-48ff-9108-08dc8f389194 X-MS-Exchange-SenderADCheck: 1 X-MS-Exchange-AntiSpam-Relay: 0 X-Microsoft-Antispam: BCL:0;ARA:13230037|1800799021|366013|376011|7416011; X-Microsoft-Antispam-Message-Info: =?us-ascii?Q?+aLuPdnNO8M8xcimLHFEK1s3FG8JJBQNgLrHxEY35YybjkDP77CgJO8Bw19U?= =?us-ascii?Q?7y0W7NquMZYiPrmGhjbrBgXoHToXr/6oCZZc5rxu2QqjM3LG3xq9LSb24tfT?= =?us-ascii?Q?Wjvq6rVBqBDq0wDawo4sPwzeU+nJPAmMWMzsXTawUYxceTD1RkuAG7JApvDr?= =?us-ascii?Q?FdDKcD68wyCNSfiXtxJKvSIIkc8xTRYPEgui0Eeza0XZGVg3HD/J+Rjyr9HF?= =?us-ascii?Q?t2nl3dW9m0SzjOBriu2Nqg3NNjFryDjyJBuk6h1oEUK03+YabmzpqUG3lLtA?= =?us-ascii?Q?Mc+XlqwMEVV0k6cYLABa/Y9ARuRsauNIZDffvdKixDCoy3Fef/dP2XtzaOWR?= =?us-ascii?Q?c5yOx0xZJTAkcuHqO1gEg2rK7E6l9Ry+0LMg3KLlOuFB0vagJV55jRq6GstV?= =?us-ascii?Q?xwzRNfrXZlzAGOeTeB7RdgDk5oPejN3MW3eyMoHkmKhWwLT8YTfl8qVNdoQR?= =?us-ascii?Q?6NWfPtOiZg8Lj/4u0HFgSjWbFjtx8CFhMKrY1H5oTe95zKNEfeqVdWuoauah?= =?us-ascii?Q?pdePtn6HY/7php6km+kZIQme7SJ1sebEjNcQ2tqc8dVEgeTLdqulgqBHvsEq?= =?us-ascii?Q?xjVub8AJjiAXrf4SexMDE4QQ7LtP3nCxS8YxMDrrADwFDIqA7kb2b1ktrQRE?= =?us-ascii?Q?KtF1pRGsAN16lSd53ZOf/QtJuRTWoyqPgLWvPJ9TfFkbhA4CQoiKtlw5zA9L?= =?us-ascii?Q?1OwBneqXIb+d6/6Pf5NwwcB/To/PMikklQ/UXBfMcjSYQyRTpmtDmm+3tOTj?= =?us-ascii?Q?Ws3ba47m6vlfUqBt/gqR6BWAjoJsWlK1PS4lciHAE3TUmPxUC2HkiaxaKoKc?= =?us-ascii?Q?Y9UwUfFgzrszGKhjleME9UIRIQlzzd+6Vl49ezKpt7RdVZO9OzCSGQAnx92j?= =?us-ascii?Q?y6dK141d4XNzN3+I6Yx8uYsx0PCAPY0C9pUG614OM7tz2WrlgDWfz98ObjDv?= =?us-ascii?Q?WZAVwsprCLa0809DlL2VczOV65FbTfELDM2t5KPvucyOrI3MeQ4l8f7ve5FI?= =?us-ascii?Q?IUD2HJxXnXBjdWgB23FPWM0HrYw9JRCiSpsyO1UB05d8I0Iy7Lfa50qLAdzj?= =?us-ascii?Q?vyPV2sUQUp0DCcGHI5hjOarnRtrmY5XxCjLUi1hAkCw4yh4hC/5aeBg5Vdlo?= =?us-ascii?Q?KtrAdTumrdYgndTZNUuiAnj1HwgtEJ/HSnm5vLGmIaGW2VAfdFQRgQp3xx/n?= =?us-ascii?Q?PFt+dXvwThFWRIncB3DfMLNSqzGNpw7vp81SU9BhHEVxyb+RAN5rT1JBZ0yP?= =?us-ascii?Q?WC0RHyWOI4UewlNL72+NyJvxW/jOP2MBgjuC51v5Q9DsPg0YIXu/m285AYvW?= =?us-ascii?Q?4hI=3D?= X-Forefront-Antispam-Report: CIP:255.255.255.255;CTRY:;LANG:en;SCL:1;SRV:;IPV:NLI;SFV:NSPM;H:DM4PR11MB6020.namprd11.prod.outlook.com;PTR:;CAT:NONE;SFS:(13230037)(1800799021)(366013)(376011)(7416011);DIR:OUT;SFP:1101; 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But > this guest-friendly behavior causes performance problems on bare metal. > So there's a 'virt_spin_lock_key' static key to switch between the two > modes. > > The static key is always enabled by default (run in guest mode) and > should be disabled for bare metal (and in some guests that want native > behavior). > > Performance drop is reported when running encode/decode workload and > BenchSEE cache sub-workload. > Bisect points to commit ce0a1b608bfc ("x86/paravirt: Silence unused > native_pv_lock_init() function warning"). When CONFIG_PARAVIRT_SPINLOCKS > is disabled the virt_spin_lock_key is incorrectly set to true on bare > metal. The qspinlock degenerates to test-and-set spinlock, which > decrease the performance on bare metal. > > Fix this by disabling virt_spin_lock_key if it is on bare metal, > regardless of CONFIG_PARAVIRT_SPINLOCKS. > > Fixes: ce0a1b608bfc ("x86/paravirt: Silence unused native_pv_lock_init() function warning") > Suggested-by: Dave Hansen > Suggested-by: Qiuxu Zhuo > Reported-by: Prem Nath Dey > Reported-by: Xiaoping Zhou > Reviewed-by: Juergen Gross > Signed-off-by: Chen Yu A gentle ping on this patch :) thanks, Chenyu