netdev - igc: missing HW timestamps at TX

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Message-ID: <VI1PR07MB4080AED64AC8BFD3F9C1BE58E18D9@VI1PR07MB4080.eurprd07.prod.outlook.com>
Date:   Sun, 17 Jul 2022 14:42:09 +0000
From:   Ferenc Fejes <ferenc.fejes@...csson.com>
To:     "netdev@...r.kernel.org" <netdev@...r.kernel.org>
CC:     Vinicius Costa Gomes <vinicius.gomes@...el.com>,
        "jesse.brandeburg@...el.com" <jesse.brandeburg@...el.com>,
        "anthony.l.nguyen@...el.com" <anthony.l.nguyen@...el.com>
Subject: igc: missing HW timestamps at TX

Hello!

There is a short story how did I end up here: [0]. We did a few measuerements with isochron and noticed many  issing timestamps. Running the isochron on the same CPU core as the igc PTP worker, the situation gets much better, yet we still have missing timestamp. Then as ladimir Oltean pointed out the problem is actually documented, so at high TX packet rates the HW timestamps migh be skipped. There is also a couter for that, so that something expected.

[0] https://github.com/vladimiroltean/isochron/issues/13