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

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Date:   Mon, 11 Apr 2022 16:36:42 -0700
From:   Vinicius Costa Gomes <vinicius.gomes@...el.com>
To:     Vladimir Oltean <vladimir.oltean@....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

Vladimir Oltean <vladimir.oltean@....com> writes:

> 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? :)

Good question. My tests were much less accurate than what you were
doing, I was basically flooding the link with preemptable packets, and
sending some number of express packets, and counting them using some
debug counters on the receiving side.


Cheers,
-- 
Vinicius