netdev - Re: [PATCH net-next v4 11/12] igc: Check incompatible configs for Frame Preemption

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Date:   Mon, 28 Jun 2021 09:20:03 +0000
From:   Vladimir Oltean <vladimir.oltean@....com>
To:     Vinicius Costa Gomes <vinicius.gomes@...el.com>
CC:     "netdev@...r.kernel.org" <netdev@...r.kernel.org>,
        "jhs@...atatu.com" <jhs@...atatu.com>,
        "xiyou.wangcong@...il.com" <xiyou.wangcong@...il.com>,
        "jiri@...nulli.us" <jiri@...nulli.us>,
        "kuba@...nel.org" <kuba@...nel.org>, Po Liu <po.liu@....com>,
        "intel-wired-lan@...ts.osuosl.org" <intel-wired-lan@...ts.osuosl.org>,
        "anthony.l.nguyen@...el.com" <anthony.l.nguyen@...el.com>,
        "mkubecek@...e.cz" <mkubecek@...e.cz>
Subject: Re: [PATCH net-next v4 11/12] igc: Check incompatible configs for
 Frame Preemption

On Fri, Jun 25, 2021 at 05:33:13PM -0700, Vinicius Costa Gomes wrote:
> Frame Preemption and LaunchTime cannot be enabled on the same queue.
> If that situation happens, emit an error to the user, and log the
> error.
> 
> Signed-off-by: Vinicius Costa Gomes <vinicius.gomes@...el.com>
> ---

This is a very interesting limitation, considering the fact that much of
the frame preemption validation that I did was in conjunction with
tc-etf and SO_TXTIME (send packets on 2 queues, one preemptible and one
express, and compare the TX timestamps of the express packets with their
scheduled TX times). The base-time offset between the ET and the PT
packets is varied in small increments in the order of 20 ns or so.
If this is not possible with hardware driven by igc, how do you know it
works properly? :)