netdev - Re: [PATCH net-next v2] net: stmmac: Caclucate CDC error only once

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Message-ID: <CAFnufp2U8Dv3yJiw+uPGOiYXxdNspmvsJ0rWKicvXTi4R32tdQ@mail.gmail.com>
Date:   Mon, 22 Nov 2021 12:29:29 +0100
From:   Matteo Croce <mcroce@...ux.microsoft.com>
To:     Kurt Kanzenbach <kurt@...utronix.de>
Cc:     "David S. Miller" <davem@...emloft.net>,
        Jakub Kicinski <kuba@...nel.org>,
        Giuseppe Cavallaro <peppe.cavallaro@...com>,
        Alexandre Torgue <alexandre.torgue@...s.st.com>,
        Jose Abreu <joabreu@...opsys.com>,
        Maxime Coquelin <mcoquelin.stm32@...il.com>,
        Voon Weifeng <weifeng.voon@...el.com>,
        Ong Boon Leong <boon.leong.ong@...el.com>,
        Wong Vee Khee <vee.khee.wong@...ux.intel.com>,
        Tan Tee Min <tee.min.tan@...el.com>,
        "Wong, Vee Khee" <vee.khee.wong@...el.com>,
        Xiaoliang Yang <xiaoliang.yang_1@....com>,
        netdev@...r.kernel.org, linux-stm32@...md-mailman.stormreply.com,
        linux-arm-kernel@...ts.infradead.org,
        Benedikt Spranger <b.spranger@...utronix.de>,
        Thomas Gleixner <tglx@...utronix.de>
Subject: Re: [PATCH net-next v2] net: stmmac: Caclucate CDC error only once

On Mon, Nov 22, 2021 at 12:19 PM Kurt Kanzenbach <kurt@...utronix.de> wrote:
>
> The clock domain crossing error (CDC) is calculated at every fetch of Tx or Rx
> timestamps. It includes a division. Especially on arm32 based systems it is
> expensive. It also requires two conditionals in the hotpath.
>
> Add a compensation value cache to struct plat_stmmacenet_data and subtract it
> unconditionally in the RX/TX functions which spares the conditionals.
>
> The value is initialized to 0 and if supported calculated in the PTP
> initialization code.
>
> Suggested-by: Thomas Gleixner <tglx@...utronix.de>
> Signed-off-by: Kurt Kanzenbach <kurt@...utronix.de>
> ---

Nit: "Caclucate" in the subject

-- 
per aspera ad upstream