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Mon, 9 Nov 2026 05:50:58 +0000 Message-ID: Date: Mon, 9 Nov 2026 13:50:48 +0800 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v2 0/6] timekeeping: Reduce magnitude of ntp_error To: David Woodhouse , Thomas Gleixner , John Stultz CC: Stephen Boyd , Miroslav Lichvar , Rodolfo Giometti , Richard Cochran , Jie Wang , Ryan Luu , Julien Ridoux , , References: <20261106030856.2538039-1-dwmw2@infradead.org> Content-Language: en-US From: "Wang, Yuan1" In-Reply-To: <20261106030856.2538039-1-dwmw2@infradead.org> Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: 8bit X-ClientProxiedBy: SI3PR02CA0003.apcprd02.prod.outlook.com (2603:1096:4:295::15) To SJ5PPFC295640A5.namprd11.prod.outlook.com (2603:10b6:a0f:fc02::852) X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Post: List-Help: List-Subscribe: List-Unsubscribe: List-Owner: Precedence: list MIME-Version: 1.0 X-MS-PublicTrafficType: Email X-MS-TrafficTypeDiagnostic: SJ5PPFC295640A5:EE_|PH7PR11MB5914:EE_ X-MS-Office365-Filtering-Correlation-Id: d799241d-40f8-47ab-c14b-08df3e256d4b X-MS-Exchange-SenderADCheck: 1 X-MS-Exchange-AntiSpam-Relay: 0 X-Microsoft-Antispam: BCL:0;ARA:13230040|366016|23010399003|376014|7416014|1800799024|22082099003|10067099003|18002099003|56012099006|11063799006|5023799004|261026121527099003|261026140227099003|261028144727099003|261022105027099003|261021135927099003|261021121427099003|261102123227099003; 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Patch 1 of this series is the fix for that: > Yuan Wang has measured it restoring their gPTP settling times (back to > 32s from 200-400s or more) and withdrawn the RFC posted in that thread > in its favour. I tested v2 on top of v7.3 (Intel mainline-tracking v7.3; kernel/time is identical to upstream v7.3), both the whole series and patch 1 on its own. Setup: two Intel i226 NICs back to back with gPTP (ptp4l + phc2sys on each end), PREEMPT_RT, NO_HZ_FULL, HZ=1000, TSC. phc2sys reads the PHC with PTP_SYS_OFFSET_PRECISE, so patch 6 is in the path. The grandmaster's PHC is stepped by +1s three times, 400s apart. The numbers are the time until the offset stays below 100ns:                                   GM phc2sys               slave phc2sys    slave ptp4l   v7.3                        207/>361/>413s       114/79/293s     34-35s   v7.3 + v2 1/6         32/32/32s                  40/41/41s         34-35s   v7.3 + v2 1-6/6     32/32/32s                  41/41/40s          34-35s ">" means it had not settled before the next step. With either kernel, the steady-state phc2sys lock is unchanged: 7-9ns rms and below 35ns peak on both ends, before the steps and in the second half of each 400s window. There were no warnings in dmesg and no ioctl errors from phc2sys. I also ran adjtime(+5ms) with nothing else adjusting the clock and measured the phase error left once the slew has finished. With patch 1 alone it was +1.5 to +8.4us over four runs. With the whole series it was +0.47 and +0.61us over two runs, so patches 2-3 visibly help there too. For the whole series: Tested-by: Yuan Wang Thanks, Yuan