netdev - Re: [RFC v3 net-next 08/18] net: SO_TXTIME: Add clockid and drop_if

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Message-ID: <20180321145930.4hlmihghljpv2wrq@localhost>
Date:   Wed, 21 Mar 2018 07:59:30 -0700
From:   Richard Cochran <richardcochran@...il.com>
To:     Thomas Gleixner <tglx@...utronix.de>
Cc:     Eric Dumazet <eric.dumazet@...il.com>,
        Jesus Sanchez-Palencia <jesus.sanchez-palencia@...el.com>,
        netdev@...r.kernel.org, jhs@...atatu.com, xiyou.wangcong@...il.com,
        jiri@...nulli.us, vinicius.gomes@...el.com,
        intel-wired-lan@...ts.osuosl.org, anna-maria@...utronix.de,
        henrik@...tad.us, john.stultz@...aro.org, levi.pearson@...man.com,
        edumazet@...gle.com, willemb@...gle.com, mlichvar@...hat.com
Subject: Re: [RFC v3 net-next 08/18] net: SO_TXTIME: Add clockid and
 drop_if_late params

On Wed, Mar 21, 2018 at 01:58:51PM +0100, Thomas Gleixner wrote:
> Errm. No. There is no way to support fd based clocks or one of the CPU
> time/process time based clocks for this.

Why not?
 
If the we have HW offloading, then the transmit time had better be
expressed in terms of the MAC's internal clock.  Otherwise we would
need to translate between a kernel clock and the MAC clock, but that
is expensive (eg over PCIe) and silly (because in a typical use case
the MAC will already be synchronized to the network time).

Thanks,
Richard