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Thu, 24 Jun 2021 14:38:46 +0000 From: Min Li To: Richard Cochran CC: "netdev@vger.kernel.org" , "linux-kernel@vger.kernel.org" Subject: RE: [PATCH net 1/2] ptp: idt82p33: optimize idt82p33_adjtime Thread-Topic: [PATCH net 1/2] ptp: idt82p33: optimize idt82p33_adjtime Thread-Index: AQHXaD6QH3kS+d8DxUyFpooG2wAFo6sihNkAgAC1sPA= Date: Thu, 24 Jun 2021 14:38:46 +0000 Message-ID: References: <1624459585-31233-1-git-send-email-min.li.xe@renesas.com> <20210624034026.GA6853@hoboy.vegasvil.org> In-Reply-To: <20210624034026.GA6853@hoboy.vegasvil.org> Accept-Language: en-CA, en-US Content-Language: en-US X-MS-Has-Attach: X-MS-TNEF-Correlator: authentication-results: gmail.com; dkim=none (message not signed) header.d=none;gmail.com; dmarc=none action=none header.from=renesas.com; x-originating-ip: [72.140.114.230] x-ms-publictraffictype: Email x-ms-office365-filtering-correlation-id: e92db02c-57fd-4b85-d672-08d9371dc61d x-ms-traffictypediagnostic: OSBPR01MB3142: x-microsoft-antispam-prvs: x-ms-oob-tlc-oobclassifiers: OLM:8273; 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charset="us-ascii" Content-Transfer-Encoding: quoted-printable MIME-Version: 1.0 X-OriginatorOrg: renesas.com X-MS-Exchange-CrossTenant-AuthAs: Internal X-MS-Exchange-CrossTenant-AuthSource: OS3PR01MB6593.jpnprd01.prod.outlook.com X-MS-Exchange-CrossTenant-Network-Message-Id: e92db02c-57fd-4b85-d672-08d9371dc61d X-MS-Exchange-CrossTenant-originalarrivaltime: 24 Jun 2021 14:38:46.5824 (UTC) X-MS-Exchange-CrossTenant-fromentityheader: Hosted X-MS-Exchange-CrossTenant-id: 53d82571-da19-47e4-9cb4-625a166a4a2a X-MS-Exchange-CrossTenant-mailboxtype: HOSTED X-MS-Exchange-CrossTenant-userprincipalname: FadfH2YSjM0I/E90Qwul4Dr5Vb51jpQVIzFGG/ZedWyoRMKfi7lSnEDX/M4ML81VRdb8tLeSUHKy80q3RRJJkw== X-MS-Exchange-Transport-CrossTenantHeadersStamped: OSBPR01MB3142 Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org > -----Original Message----- > From: Richard Cochran > Sent: June 23, 2021 11:40 PM > To: Min Li > Cc: netdev@vger.kernel.org; linux-kernel@vger.kernel.org > Subject: Re: [PATCH net 1/2] ptp: idt82p33: optimize idt82p33_adjtime >=20 > On Wed, Jun 23, 2021 at 10:46:24AM -0400, min.li.xe@renesas.com wrote: > > From: Min Li > > > > The current adjtime implementation is read-modify-write and > > immediately triggered, which is not accurate due to slow i2c bus > > access. Therefore, we will use internally generated 1 PPS pulse as > > trigger, which will improve adjtime accuracy significantly. On the > > other hand, the new trigger will not change TOD immediately but delay i= t > to the next 1 PPS pulse. >=20 > Delaying the adjustment by one second (in the worst case) will cause > problems. User space expects the adjustment to happen before the call to > adjtimex() returns. >=20 > In the case of PTP, if new Sync messages arrive before the delayed > adjustment completes, there will be a HUGE offset error, and that will hu= rt > the PI servo. >=20 > So it is better to accept a less accurate jump then to delay the adjustme= nt. >=20 > Thanks, > Richard Hi Richard Thanks for the review For linuxptp/ptp4l, we can use step_window to adapt to the slow adjtime. I have tested this change with ptp4l for by setting step_window to 48 (assu= ming 16 packets per second) for both 8265.2/8275.1 and they performed well. Min