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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=coWda/k9IouttF7c2IlLgWtAZ4QLMG93DOX9yngDXj0=; b=qhI4gHXWxCUhJllbLpJ1WvI0RaiPpfHWpmgCmMemEUxSurSyMHi73DvlprJ76WCi5J4PYzhOv2AokVnbI5sELJqNaSMubQCx10Rye5FUUyzEtO/KdllpCG9ARhuGywAGty2OSH4sh4U+TTZ8udXe7wlgefceZWF29q8rA3eSr9Y= Subject: Re: [PATCH v1] domctl: hold domctl lock while domain is destroyed To: Julien Grall , Jan Beulich CC: George Dunlap , Ian Jackson , Stefano Stabellini , Wei Liu , , Dmitry Isaikin , , , Paul Durrant References: <2e7044de3cd8a6768a20250e61fe262f3a018724.1631790362.git.isaikin-dmitry@yandex.ru> <22a4b3c7-7faa-607b-244a-0ab99d7ccfa9@suse.com> <16d43ba8-d45f-021c-0e19-e233cb967938@citrix.com> <01ec71a5-a1f1-b7db-d467-bc4c734db096@xen.org> From: Andrew Cooper Message-ID: <0fa0d369-c67c-1cdd-0ff8-1542487ffb8a@citrix.com> Date: Fri, 17 Sep 2021 10:41:30 +0100 User-Agent: Mozilla/5.0 (X11; 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X-MS-Exchange-AntiSpam-MessageData-ChunkCount: 1 X-MS-Exchange-AntiSpam-MessageData-0: =?utf-8?B?RnBEbXlLK0tZZDhLWE1ncU14a0JNOERUejV1UjZGOWd1d3l1MW9kZmdlWjhs?= =?utf-8?B?OVpOUWs0YWFybS9PYURDU2xuUUR3Y3luSVBHdUpZQW0raElUTjI4MW9nZ0hJ?= =?utf-8?B?bE9MUW5wMEt3OVFDMG02bjFKVG4waXpMOGEzWXpRVkljNEVNNDN2WCtiRnEw?= =?utf-8?B?VmVmSjBwcHNvL2NjT21oV0EyZWovZEdydXp0aXJDNVlBUWJWUVR5WXdCT01Q?= =?utf-8?B?cmx4b3dLb2kyNUpna1ZDaS9oTnVWMy9pNlhTZEJ5a0VnZkRmcTBEWDROTTJ1?= =?utf-8?B?SEpleHBKS2orWE54RC9ySEEwSzNkNWN5TGprQUpaMmVycDFnckFXeGhRTjlB?= =?utf-8?B?cWcrMzNPZGJDbGJDbnpIS0JiTFNWMERwdGp1REdxN3Q4L0lUbUQ1ZTJrdUNp?= =?utf-8?B?NEtMZ2tNeTA4SGI2NnlveEdmODYyQlBkRFc3S3J1d0tjNGtnb3FKc2pRTlRF?= =?utf-8?B?cVFRK1o3eWExVGs0T05ROXYzS0N5bFN5NjhMaHl5cGZvdHVxN0pPYzJaUXE5?= =?utf-8?B?ampDY1Zjd0V0dTYzL2pIZUlIR25jQzJURlR1TC9ROG9MSGxOOFR1bm9YSHFl?= =?utf-8?B?c2tSTXFxeEdsdTgzK21JMTh3Mnd5aWs2S3RUNUxtNCtrcEZXbVJNdFg3T3NP?= =?utf-8?B?ZVYyS0RUVE5zdHpPM3dTbjdwT0xxemRQcXVhQWJ5M2ViSmhFQ1hROXRFeVFj?= =?utf-8?B?M29zMU9mQ21rbXk1eDdHMDBnYi92bDZDMUVLc2ZxZEViVk5sK3diSk1mcURX?= =?utf-8?B?K25iM0pzMDFJODFQUDBUWWhFSm1MamxnS2NTem9jS1ZUSDJ4bVRkMjFxY216?= =?utf-8?B?YTkvbmEycHRUc2JaVjJuV2VUZ1RuUWR3L3F5V29YbFZsdzg4ZWNTZ0dVb1pj?= =?utf-8?B?V1BBQjlsR0tLRUk1NkU3ZFJxdEtHd1JWSnlZSEtFSXBZQlpFN3JNRXp6M0hF?= =?utf-8?B?VDdVeWxPTTIzMTdNY1pmakl6YmlEQjI2aFl4RzZUNzB4L0c4VmNBenVDK0FE?= =?utf-8?B?YW5GMnB2UG90UGtTaDIxTWQySnRWenNhL0ZQVEU0Y29qcExTTXdpVW81M083?= =?utf-8?B?VTZyREpVM3RKK2lzMjRMZ3kwVjlSVno4UDFzZ29JWHZTS3JCK0hydFJSVEw3?= =?utf-8?B?YitBNHhJSXJZWFhuNUsvRThkdmdzNXA3Y2dlWFg5QVZ4RkpRNHNoaVQwbVBa?= =?utf-8?B?bEE2K3VQZmxqY211cVpMZjBNbExIdHh6STdOVDByR29TTzFRRW5xSU8yRlJa?= =?utf-8?B?eDl3bGxVVEVNNWJXUUc4V3VlMVBsbXhrNUZVOWdQZ2R1QXNyN0tINXdPNHVS?= =?utf-8?B?dVQ5Ti9pbm1kTXBTNGJQQkhTZ1c3aHAyM0Q5OGtkT1hwYktkWmkrdUs0TWM2?= =?utf-8?B?VER1K1FmWlRLMzdBTXIzUW54NjRhcWE4YWdhR3cxbTJkbDNwOWY3Rno0cmRq?= =?utf-8?B?Mnp6b0x2QTRhSVk2clU2YU8rc3JTUjlUUFB3VldHN1BiZ1NpZmtWSVg0M1p4?= =?utf-8?B?cHg3V2NlcStEREZyVW1FWE56Tlc4V3M3TmMwR2hzVmJvdE9HRFNHQ3BRMHZG?= =?utf-8?B?LzFUMmd0bTA1ZU5abEl6WWpCQWhVOHpMVDdKeDd4V0pZU2hTNnkxcnRXK0tL?= =?utf-8?B?ZmxjeStzSWpXa0I1U0dLUngwcnpYQXVTZ09VUWFIU1FNcGZ5TlE1bDExOS95?= =?utf-8?B?SytURk9ZTi9mUVZweDVRYUo2ZFFESS85anJiRkI0V0g0a1RPYm51alR1djhi?= =?utf-8?Q?INWZVtmYs0EToh5HI8sdZn9ifLxNe0ktKpHdNsG?= X-MS-Exchange-CrossTenant-Network-Message-Id: 020039dc-925d-45f8-e1d0-08d979bf5865 X-MS-Exchange-CrossTenant-AuthSource: BYAPR03MB3623.namprd03.prod.outlook.com X-MS-Exchange-CrossTenant-AuthAs: Internal X-MS-Exchange-CrossTenant-OriginalArrivalTime: 17 Sep 2021 09:41:38.1120 (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: fzBb2cPpCTP98bKSgqo5yAKJW4QCM0sXZllFf87gatzk8JLZaYBA2PH8cprbHg9KGt+tH6aAPInrZpqpreD/lIeOx+jCIlf+bMprdZkD5e4= X-MS-Exchange-Transport-CrossTenantHeadersStamped: BY5PR03MB5045 X-OriginatorOrg: citrix.com On 17/09/2021 10:27, Julien Grall wrote: > Hi, > > (+ some AWS folks) > > On 17/09/2021 11:17, Jan Beulich wrote: >> On 16.09.2021 19:52, Andrew Cooper wrote: >>> On 16/09/2021 13:30, Jan Beulich wrote: >>>> On 16.09.2021 13:10, Dmitry Isaikin wrote: >>>>> From: Dmitry Isaykin >>>>> >>>>> This significantly speeds up concurrent destruction of multiple >>>>> domains on x86. >>>> This effectively is a simplistic revert of 228ab9992ffb ("domctl: >>>> improve locking during domain destruction"). There it was found to >>>> actually improve things; >>> >>> Was it?  I recall that it was simply an expectation that performance >>> would be better... >> >> My recollection is that it was, for one of our customers. >> >>> Amazon previously identified 228ab9992ffb as a massive perf hit, too. >> >> Interesting. I don't recall any mail to that effect. > > Here we go: > > https://nam04.safelinks.protection.outlook.com/?url=https%3A%2F%2Flore.kernel.org%2Fxen-devel%2Fde46590ad566d9be55b26eaca0bc4dc7fbbada59.1585063311.git.hongyxia%40amazon.com%2F&data=04%7C01%7CAndrew.Cooper3%40citrix.com%7C8cf65b3fb3324abe7cf108d979bd7171%7C335836de42ef43a2b145348c2ee9ca5b%7C0%7C0%7C637674676843910175%7CUnknown%7CTWFpbGZsb3d8eyJWIjoiMC4wLjAwMDAiLCJQIjoiV2luMzIiLCJBTiI6Ik1haWwiLCJXVCI6Mn0%3D%7C1000&sdata=si7eYIxSqsJY77sWuwsad5MzJDMzGF%2F8L0JxGrWTmtI%3D&reserved=0 > > > We have been using the revert for quite a while in production and didn't > notice any regression. > >> >>> Clearly some of the reasoning behind 228ab9992ffb was flawed and/or >>> incomplete, and it appears as if it wasn't necessarily a wise move in >>> hindsight. >> >> Possible; I continue to think though that the present observation wants >> properly understanding instead of more or less blindly undoing that >> change. > > To be honest, I think this is the other way around. You wrote and merged > a patch with the following justification: > > " >     There is no need to hold the global domctl lock across domain_kill() - >     the domain lock is fully sufficient here, and parallel cleanup after >     multiple domains performs quite a bit better this way. > " > > Clearly, the original commit message is lacking details on the exact > setups and numbers. But we now have two stakeholders with proof that > your patch is harmful to the setup you claim perform better with your > patch. > > To me this is enough justification to revert the original patch. Anyone > against the revert, should provide clear details of why the patch should > not be reverted. I second a revert. I was concerned at the time that the claim was unsubstantiated, and now there is plenty of evidence to counter the claim. ~Andrew