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Thu, 5 Mar 2020 04:47:29 +0000 Received: from sc2-cpbu2-b0737.eng.vmware.com (66.170.99.1) by DB6PR1001CA0022.EURPRD10.PROD.OUTLOOK.COM (2603:10a6:4:b7::32) with Microsoft SMTP Server (version=TLS1_2, cipher=TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384) id 15.20.2772.16 via Frontend Transport; Thu, 5 Mar 2020 04:47:25 +0000 From: Vivek Thampi To: David Miller CC: "richardcochran@gmail.com" , "linux-kernel@vger.kernel.org" , "netdev@vger.kernel.org" , Pv-drivers , "virtualization@lists.linux-foundation.org" , "x86@kernel.org" , Thomas Hellstrom , "jgross@suse.com" Subject: Re: [PATCH RESEND] ptp: add VMware virtual PTP clock driver Thread-Topic: [PATCH RESEND] ptp: add VMware virtual PTP clock driver Thread-Index: AQHV7fh9sGmTv3Q/nkCcjzOFcD8fwKg5BbgAgABwnYA= Date: Thu, 5 Mar 2020 04:47:28 +0000 Message-ID: <20200305044713.GA173879@sc2-cpbu2-b0737.eng.vmware.com> References: <20200228053230.GA457139@sc2-cpbu2-b0737.eng.vmware.com> <20200304.140410.731261448085906331.davem@davemloft.net> In-Reply-To: <20200304.140410.731261448085906331.davem@davemloft.net> Accept-Language: en-US Content-Language: en-US X-MS-Has-Attach: X-MS-TNEF-Correlator: x-originating-ip: [66.170.99.1] x-clientproxiedby: DB6PR1001CA0022.EURPRD10.PROD.OUTLOOK.COM (2603:10a6:4:b7::32) To SN6PR05MB5326.namprd05.prod.outlook.com (2603:10b6:805:b9::27) authentication-results: spf=none (sender IP is ) smtp.mailfrom=vithampi@vmware.com; 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x-microsoft-antispam-message-info: y06snQYR8TAAYGVjlaxyxi8N0S3mrJm66x93S8kqbGP1Sr9QFr6+Gw3irazbV2emA1ZfYgTDAmEwCM6RB67jR4Ts7xeNl9+CnayzdbRSrCrIsOvz6VjUN8wCmqv6THf7FGHHUWmcIuA5KE9NG9vLGTADRcYVUrVoPlSH20ecvaTb71CwaYc3QmrPx7pHodhTqR99/X91u/W3GvJnnTkb5kO3TKont1RvF+v5o9PcoO8e8wIgKrURNQ6yhwqSAAIbMz8g6FfkvKqyV+iZ4rbw6ymvXatf4YUQ3JUTafVMwPV8kwJWxGZuHetrMDdJO3OX6EI4ClL2gFyod8aWr/HzqL44X2KA/aalIozRXL6YNr99j9hcRMZ4lWGUAiBkBZffsx/JsznKAIItO5kAhfgOO5KiU+ck9Mig3BJmx+HfYkL1WHqLIVwDM6z8VrGP2jwo x-ms-exchange-antispam-messagedata: 6bJxoQttOsJGHSAHMcz37ZcEaBgwNLS53BxM/tBD1Js25QopnvtiYaQkqIJpmo+UWn5UaKqIYtPpWXcEYjOnKcEfG3eakd/9Q2nU7nfAq6W5b+TKZrFApbluQCdDdjjDLOy0zyb6+ilaIoJxjBTn0w== Content-Type: text/plain; charset="us-ascii" Content-ID: Content-Transfer-Encoding: quoted-printable MIME-Version: 1.0 X-OriginatorOrg: vmware.com X-MS-Exchange-CrossTenant-Network-Message-Id: 968b98a2-6bdf-478a-758e-08d7c0c04eb6 X-MS-Exchange-CrossTenant-originalarrivaltime: 05 Mar 2020 04:47:28.7876 (UTC) X-MS-Exchange-CrossTenant-fromentityheader: Hosted X-MS-Exchange-CrossTenant-id: b39138ca-3cee-4b4a-a4d6-cd83d9dd62f0 X-MS-Exchange-CrossTenant-mailboxtype: HOSTED X-MS-Exchange-CrossTenant-userprincipalname: xhm8nGB6qxeCvwwg8TB8v5CWVT6nWfn/KtYZoRCAETpUXttDHZqTZ8SEfC9zAANDN9Iz22czZVgfXGmAcZX07A== X-MS-Exchange-Transport-CrossTenantHeadersStamped: SN6PR05MB4992 Sender: netdev-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: netdev@vger.kernel.org Thanks for taking a look, David. On Wed, Mar 04, 2020 at 02:04:10PM -0800, David Miller wrote: > From: Vivek Thampi > Date: Fri, 28 Feb 2020 05:32:46 +0000 >=20 > > Add a PTP clock driver called ptp_vmw, for guests running on VMware ESX= i > > hypervisor. The driver attaches to a VMware virtual device called > > "precision clock" that provides a mechanism for querying host system ti= me. > > Similar to existing virtual PTP clock drivers (e.g. ptp_kvm), ptp_vmw > > utilizes the kernel's PTP hardware clock API to implement a clock devic= e > > that can be used as a reference in Chrony for synchronizing guest time = with > > host. > >=20 > > The driver is only applicable to x86 guests running in VMware virtual > > machines with precision clock virtual device present. It uses a VMware > > specific hypercall mechanism to read time from the device. > >=20 > > Reviewed-by: Thomas Hellstrom > > Signed-off-by: Vivek Thampi > > --- > > Based on feedback, resending patch to include a broader audience. >=20 > If it's just providing a read of an accurate timesource, I think it's kin= da > pointless to provide a full PTP driver for it. The point of a PTP driver for this timesource is to provide an interface that can be consumed by Chrony (and possibly other applications) as a reference clock for time sync. This is admittedly a very basic first step providing just PTP_SYS_OFFSET functionality (which gets us to <1us VM-host time sync). Down the line, I also intend to introduce cross-timestamping for more precise offsets. Using the PHC infrastructure seems like a good fit for this, but please let me know if I'm missing something or misinterpreting your comment. Thanks.