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Tsirkin" , Jason Wang , Xuan Zhuo , Richard Cochran , netdev@vger.kernel.org, Marc Zyngier , Mark Rutland , Daniel Lezcano , Thomas Gleixner , linux-arm-kernel@lists.infradead.org References: <20231218073849.35294-1-peter.hilber@opensynergy.com> <20231218073849.35294-6-peter.hilber@opensynergy.com> Content-Language: en-US In-Reply-To: Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit X-ClientProxiedBy: BE0P281CA0007.DEUP281.PROD.OUTLOOK.COM (2603:10a6:b10:a::17) To BE1P281MB1906.DEUP281.PROD.OUTLOOK.COM (2603:10a6:b10:3d::8) 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: BE1P281MB1906:EE_|FR3P281MB2798:EE_ X-MS-Office365-Filtering-Correlation-Id: 76d02d69-742c-43c7-b28f-08dc9120a81b X-MS-Exchange-SenderADCheck: 1 X-MS-Exchange-AntiSpam-Relay: 0 X-Microsoft-Antispam: BCL:0;ARA:13230037|366013|376011|7416011|1800799021; X-Microsoft-Antispam-Message-Info: =?utf-8?B?eVZpK2wwZFJVVlVwYU9TaW5ITHBETUZ1aHhQVnFYQ0dsWktGTllBc2Z5RG9N?= =?utf-8?B?K0t0cVZhVk8xTkZPZUdqT1VjQlQ2Z2NZYkhZNGhsc0JLVkVUcVNjVlFYcXlt?= =?utf-8?B?dkRwZWZ5WUdoTnhmSVVoNDlUKzZ3UWVZWUx5bjBwempCdkhQTnorclpzblhh?= =?utf-8?B?d1p1MnMyN1Q3cFdzclRLVTJKaE92U2phTUtlNTFiUytMbU5MQ01NNHZQUTJS?= =?utf-8?B?eVR6RGJiWFFxZ1hFdlJqNTlwaGExR0VRdnZOYkpOQkRIejRnMUh1K1N5Nnli?= =?utf-8?B?RW51T2d6UmVSVmxJMjJ4d05SWU1GeTVSQ2FMS0tRa2duZURVcXIyeVRKZ3Rn?= =?utf-8?B?amQzcUl5bEVoRnVNeGZjbjBtZTcrbHUydmJZY3FZbWx6a21FOVJSbjhIczlD?= =?utf-8?B?cUJNcUFVSjU2MjlYMzdGN3VjemFWVmFKenJaQ3NyL3FEa0pyQ3dCdER1d1Iz?= =?utf-8?B?ZjJOSW9HYlBjc1pmS3ZuR0lMODZtTitJdFdMdjkrbHBPM0VvOEtoRXNTOC9F?= =?utf-8?B?dndIWEhWVW5GL0hvZ09XZ2tVbyt2dk5COWswekdQdEV3TWtaT2ZxQ0R6VUt3?= =?utf-8?B?enRFQkx4MlQrNVV6YlhPWUtzYzVqV3VsK3NjM21lbG9jWGd0UWxZelZhUXMy?= =?utf-8?B?dWhFN0hNN2JJdkQrNjdVOU5SejhFaU9BU3N5S2xlL3lyY3YyNUdPL1lVQTRF?= =?utf-8?B?R0hWOWhPYmxBWE94bUlYeHFOK2p6cVhrQUhiTDVHT3FLYTlaUi9YWHNIanpP?= =?utf-8?B?amJxN0FvNjVEb053c3dYS0FlVEtORk95OEhkOUdYZkd3K1B5YlhSTUZIWkNH?= =?utf-8?B?d05uYmtqQTdyY21LNFZvbGJRbTNORnY4eHROaHpkdmtNYWJ2QXFhN083MlFx?= =?utf-8?B?L1pYSG9EVW1jTmo4MTFCa2FMVENGQmxVcHF3bkozN09ZK0hEaWc0ZU5pMDA0?= =?utf-8?B?NnNwM1ErbWIwTXhjN0pTU2taamtVaWhUM3FseENXNXB6d2FLd3duckNVbnBt?= =?utf-8?B?UE0wcGpoSnNXNzN0MFBvZG94TU1idkw0YlhVZkZldkVKUldXdzBHeXROY2NU?= =?utf-8?B?enhLSEVqclZ0OFZKRGJBVUxkdzQ5eFlWYWJiVlRhdXB5aFIyVmFIUDZxb0ty?= =?utf-8?B?RVhCMEdydWgrVjhEbXMwNDJ3cFVLNWlwS2Eza2Fzd2JIMUs0QmdXV00vVWUr?= =?utf-8?B?dGZTRzFoU2tFbFEyVnBIWDJRaUtLcllkVndFNXVJYTU5bHl1b2dFa2ZKeFc3?= =?utf-8?B?YzA3c3d6bWJ0Kzlvc3J5NkdBS2VPdUFzc04wN2Z1Z2FOSkJoaUZRTkxiU0F3?= =?utf-8?B?bllUNldwQThtTHRPWmVHQlY1Zms5d3FwVVVLK3R0emM3YjF3UlZXT3cvQno1?= =?utf-8?B?UVhBZ05DanNVS0VHdWUyYkNhYTVsaWkwQlp0Qi81Wk1HNTFRbzUrYUxuMjRW?= =?utf-8?B?NzZ2WWkwVHk5VGVOZUh1K2hMa0pYc3ljQm5DK1pVL1czSHllbFdCYmV3bWJN?= =?utf-8?B?MGhPM0F5ZDRqSVNkRWRkdHdxZ3lMeHAxQk5jS21XelFHOGRmcGEzQW85elJt?= =?utf-8?B?WjlKTzdaUFQ0cTNwTTI1VzJ5M0tFVjB1eGk2RHkzUTEwUDBPejRNNVc4U084?= =?utf-8?B?MTkzcEtpT3ZvNm9rQXJmMDNveDZvTTJuK3FhQjVOMjNIOWc4Umowaml4dDhz?= =?utf-8?Q?ovNZXu8Z1FkIN4IrzPCi?= X-Forefront-Antispam-Report: CIP:255.255.255.255;CTRY:;LANG:en;SCL:1;SRV:;IPV:NLI;SFV:NSPM;H:BE1P281MB1906.DEUP281.PROD.OUTLOOK.COM;PTR:;CAT:NONE;SFS:(13230037)(366013)(376011)(7416011)(1800799021);DIR:OUT;SFP:1102; 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a=rsa-sha256; c=simple/simple; d=opensynergy.com; s=TM-DKIM-20210503141657; t=1718884865; bh=dYQ8c40brY8P1cnuVvGfvMzzVVZR8lVQzDZOZTE2mDI=; l=2040; h=Date:From:To; b=LdNdEYPh6ket7UodAG5jrQ2KtlgYq8TqI8SfoJwl2ZGnBitd1MPCJNveLIkyb3yLg LhQgo7PZtXHZLfTjg9TO+zumgk11tN8I06tXZF4IR6x+37AGTR3uB3KoeegG0xBZYI 7Rp1f9Ij9RaOnZqsqXTuZA2+/myv90epHyn6FZUpsPVtcBTeSYBa4A0ZxbnLduTCTo NYxATFFBEuYXsfPlH04fpzYOPMzyY94dHwQzq/rB5c0XD/bQO/Ol2L517V4fzQuhxo 1mo0ILUL1QMWaWasOQ800yGjLMX19UBUott+9pfbi2oUIHb2JOswQENHpg2O5vHJXe EcxRLdqPLkjoQ== On 15.06.24 10:01, David Woodhouse wrote: > On Mon, 2023-12-18 at 08:38 +0100, Peter Hilber wrote: >> >> + ret = viortc_hw_xtstamp_params(&hw_counter, &cs_id); >> + if (ret) >> + return ret; >> + >> + ktime_get_snapshot(&history_begin); >> + if (history_begin.cs_id != cs_id) >> + return -EOPNOTSUPP; > > I think you have to call ktime_get_snapshot() anyway to get a snapshot > from before your crosststamp? But I still don't much like the fact that > you need to use it to work out which cs_id is being used. The actual cs_id check is in get_device_system_crosststamp(), where it was added recently [1]. So this additional check is just verifying that the history_begin is usable. > > Shouldn't get_device_system_crosststamp() pass that to its get_time_fn > as a hint? This is unneeded in this case, since get_device_system_crosststamp() does the check already (but the driver is free to pass it through the get_time_fn parameter ctx). > > On x86, you are likely to find that history_begin.cs_id is the KVM > clock, so this will return -EOPNOTSUPP and userspace will have to fall > back to PTP_SYS_OFFSET. I note the KVM PTP clock actually *converts* a > TSC-based crosststamp to kvmclock µs for itself, so that it can report > *cs_id = CSID_X86_KVM_CLK. Not sure how I feel about that though. I'm > inclined to suggest that it shouldn't, as anyone who wants accurate > timekeeping shouldn't be using the KVM clock anyway. > > But we should at least be relatively consistent about it. ATM, the driver does indeed not have TSC support (for cross-timestamping) enabled at all, so would always use fallback. If *not* using the KVM clock, I think TSC can just be enabled by adding architecture-specific code similar to virtio_rtc_arm.c. I am not familiar with the KVM clock, but maybe it would be sufficient to allow CSID_X86_KVM_CLK as well? Thanks for the comments, Peter [1] https://git.kernel.org/torvalds/c/4b7f521229ef