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mx.microsoft.com 1; spf=pass smtp.mailfrom=citrix.com; dmarc=pass action=none header.from=citrix.com; dkim=pass header.d=citrix.com; arc=none DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=citrix.onmicrosoft.com; s=selector2-citrix-onmicrosoft-com; h=From:Date:Subject:Message-ID:Content-Type:MIME-Version:X-MS-Exchange-SenderADCheck; bh=MS1C3GDXefObJ0bo182MCU8ca10mlA45jZClpTpeywY=; b=jfCLwlxXeltHba5BqYizOEHHd7jMdXzUFzE0ne7p0Gd9fcbHd5sQHj4IA3E4CKf5JitYS46LDILAZllvglV6zgZkR0j9AAofKgx+wmDjwZvEttJbrGf0K39lE2U5UjYPq7Zc1ekclwP4/GObIIxvrP/w4z/1C7MOmbhCR5mV1c0= Date: Tue, 20 Apr 2021 17:44:53 +0200 From: Roger Pau =?utf-8?B?TW9ubsOp?= To: Jan Beulich CC: "xen-devel@lists.xenproject.org" , Andrew Cooper , Wei Liu Subject: Re: [PATCH v4 1/3] x86/time: latch to-be-written TSC value early in rendezvous loop Message-ID: References: <35bbad56-d0f0-a37d-674c-e635eaf9c94c@suse.com> Content-Type: text/plain; charset=utf-8 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: <35bbad56-d0f0-a37d-674c-e635eaf9c94c@suse.com> X-ClientProxiedBy: MR1P264CA0033.FRAP264.PROD.OUTLOOK.COM (2603:10a6:501:2f::20) To DS7PR03MB5608.namprd03.prod.outlook.com (2603:10b6:5:2c9::18) MIME-Version: 1.0 X-MS-Exchange-MessageSentRepresentingType: 1 X-MS-PublicTrafficType: Email X-MS-Office365-Filtering-Correlation-Id: 472bb0ab-30f3-42bd-b1f3-08d904134139 X-MS-TrafficTypeDiagnostic: DM6PR03MB3482: X-MS-Exchange-Transport-Forked: True X-Microsoft-Antispam-PRVS: X-MS-Oob-TLC-OOBClassifiers: OLM:5516; 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X-MS-Exchange-AntiSpam-MessageData: =?utf-8?B?N2svOHYxRHVjcmVieDV2eW5sbW1HNitwNGoyVE9NVmJFbThlaXJqaWZORXQ0?= =?utf-8?B?TjdNSVkzV1ZwdGpFWU5aU0ZhSDZPK1JGamJPVUJsZ1FDZnNlTU50ZXgzQnFW?= =?utf-8?B?Q1ZSWHNwSFNHN2x6dzR1emQxV3pxQzhuSFpUN0VmS2s5aEQ3RzRoQXQ4cVQx?= =?utf-8?B?bkZ0dVhpcC82VU8wV0JoSGw5a3k2bUJaejcyNUtKWTVVZGtDZmVKc1BNN1dn?= =?utf-8?B?SUNoUktYTVdEb2w5RmJySHBEOFFNb1BreTI4Y3lpaVZjSkZmcmVXV01YTGFE?= =?utf-8?B?V3c5bytqYzVFQmtsd1czU3kzems0aHJrRHFOR3I5THpYK0FrdjJpb3A3dkkz?= =?utf-8?B?QmwxSEluVmt4dWZab3dBQWxVVEhJVy95VC9vS2JQUFNZQU1zbVdxY1BaQ1RM?= =?utf-8?B?b2Njdk9LVkVDeXh4TjR4UmpSN1FReTRna3E3dVNnR0xLYVBHblhwTFpPZ0RQ?= =?utf-8?B?R1I4ems0QnF4c21tRXdtbnNxNnovbDRUKzNDanowa1VUQ29hZ24wVzI3a2sy?= =?utf-8?B?N21aNmJxNjlyVFBUVGhld1NQcGFWdGxxb1M3YkNBaVdicGNxYlFJdWM2Nm1O?= =?utf-8?B?TlJLTEFNR21zWXI4dWVzZGZTS1dieG8zTC9HbWNYZEJ1T3hjRTB0MUQzSFBI?= =?utf-8?B?UjdDeHpqT3RqZGtNQ1FBRWtsYmd3b2szY29sWlJ6MWpEdm5mdEliYXhYWWc0?= =?utf-8?B?eWdHZGp2a2Z2RVNDM3NjZUFQdlpUY2M1M04veGE3Y3hsZHFwcTRiRm5aeTVI?= =?utf-8?B?amlPUXhuVTVmYnptcVZDRVo1NnZvTDEwWkl0QmZsOVVqWVRKOWw2M0xYYW1E?= =?utf-8?B?bXFEbUl6Tjg4V2RPK0NFNUZzOWxWcmpmZUVGTkFpb3lBNTAzREMvaDAyQlcr?= =?utf-8?B?dkVSeEdENEZKNDlsRnhsZG5RK3EranNSb1BUOWs0azdNNlg5M21YWnVWTXRW?= =?utf-8?B?c3FCUFJabTVQZ21URXVLVnc2QXE4Tm9lWXJEc3ZGU3FSQytCdkFxV3RIM2Fk?= =?utf-8?B?VXAzS2dIZ3BwMHJoSEFUdFppR1lGNFJKSDA2c0VxM0V1NE1FZnhuS1ZvRmNy?= =?utf-8?B?MFhTKzdDNmQ0QWQ1bzhjWjhWSEg4U0ozTE8rVWpJREtmZ0o2Qzhtdk1iK1do?= =?utf-8?B?emJubjlIMW1MK2hMWUpGTDAwVG1DeHl4MHlyWnNxUlpYN0NZaXQ5T1VlMzlH?= =?utf-8?B?VWdjaXFMNXduajRtM3BURTNYMWxHSXdPb2lTUThMellYcWtVU08zZ3pPYmhH?= =?utf-8?B?UlA0MVQzb2gxVzRoYmFPUGRGeHNTRCszSndRTFV6UW93ZUdiL2J3K2U0THgw?= =?utf-8?B?N3JERklZU09HblFhZlFXNnA3VnhNNUt0Qm5ZYkc3aFI0bnFrUFlkQ0JEazMx?= =?utf-8?B?TDNkYjhyV0huQUVmcmREMlRuQ1VVc2Z4a3E1U3hTQ01TOTlmUytQZ2szVlNO?= =?utf-8?B?a25GSUJZNzVOK0hPZnE4WlNXblNwRnc2NklOMEl0NXo4MjBrdHdCYUp3SlN5?= =?utf-8?B?UEYxTHliZmJTVjFKSWlmMC9MVThObzFUcU82Ull3WHZPN1FFT3UyL0xKb2ox?= =?utf-8?B?N25RdFIrbWNPQktheUZBUmNrNllobmRXRW1SQzAzOVlwUE5kZE5jWTc5RW5G?= =?utf-8?B?eDB6Tnd6ZWl1Q2FVTzMvR283akg2dWhmTWk2THdNaDFWRWRTTkwrOUd1Tjdt?= =?utf-8?B?WVRRYmRnVkVmblI4UmlPV0NCKzRNMWlNVWMzcHFqU3FRTWdjR2hNMTEvQmRo?= =?utf-8?Q?HvIm23nxO/SEalxdF1UaDy/lf73O+Gp927uBi+t?= X-MS-Exchange-CrossTenant-Network-Message-Id: 472bb0ab-30f3-42bd-b1f3-08d904134139 X-MS-Exchange-CrossTenant-AuthSource: DS7PR03MB5608.namprd03.prod.outlook.com X-MS-Exchange-CrossTenant-AuthAs: Internal X-MS-Exchange-CrossTenant-OriginalArrivalTime: 20 Apr 2021 15:44:59.5891 (UTC) X-MS-Exchange-CrossTenant-FromEntityHeader: Hosted X-MS-Exchange-CrossTenant-Id: 335836de-42ef-43a2-b145-348c2ee9ca5b X-MS-Exchange-CrossTenant-MailboxType: HOSTED X-MS-Exchange-CrossTenant-UserPrincipalName: KbEYHBdEBYgoDL62YC7m/kJV6iVAMzZ419x1ebpvSZk+RRe/TWs3wXrl1XMDJSoVEAAbpNvhZEHsQ4Buzjf13A== X-MS-Exchange-Transport-CrossTenantHeadersStamped: DM6PR03MB3482 X-OriginatorOrg: citrix.com On Thu, Apr 01, 2021 at 11:54:05AM +0200, Jan Beulich wrote: > To reduce latency on time_calibration_tsc_rendezvous()'s last loop > iteration, read the value to be written on the last iteration at the end > of the loop body (i.e. in particular at the end of the second to last > iteration). > > On my single-socket 18-core Skylake system this reduces the average loop > exit time on CPU0 (from the TSC write on the last iteration to until > after the main loop) from around 32k cycles to around 29k (albeit the > values measured on separate runs vary quite significantly). > > Signed-off-by: Jan Beulich Reviewed-by: Roger Pau Monné Thanks, Roger.