netdev - Re: [PATCH net-next 2/2] net: enetc: count the tc-taprio window drops

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Message-ID: <20210602101920.3c09686a@kicinski-fedora-PC1C0HJN.hsd1.ca.comcast.net>
Date:   Wed, 2 Jun 2021 10:19:20 -0700
From:   Jakub Kicinski <kuba@...nel.org>
To:     Vladimir Oltean <olteanv@...il.com>
Cc:     "David S. Miller" <davem@...emloft.net>, netdev@...r.kernel.org,
        Claudiu Manoil <claudiu.manoil@....com>,
        Michael Walle <michael@...le.cc>, Po Liu <po.liu@....com>,
        Vinicius Costa Gomes <vinicius.gomes@...el.com>,
        Vladimir Oltean <vladimir.oltean@....com>
Subject: Re: [PATCH net-next 2/2] net: enetc: count the tc-taprio window
 drops

On Wed,  2 Jun 2021 15:21:14 +0300 Vladimir Oltean wrote:
> From: Po Liu <Po.Liu@....com>
> 
> The enetc scheduler for IEEE 802.1Qbv has 2 options (depending on
> PTGCR[TG_DROP_DISABLE]) when we attempt to send an oversized packet
> which will never fit in its allotted time slot for its traffic class:
> either block the entire port due to head-of-line blocking, or drop the

the entire port or the entire queue?

> packet and set a bit in the writeback format of the transmit buffer
> descriptor, allowing other packets to be sent.
> 
> We obviously choose the second option in the driver, but we do not
> detect the drop condition, so from the perspective of the network stack,
> the packet is sent and no error counter is incremented.
> 
> This change checks the writeback of the TX BD when tc-taprio is enabled,
> and increments a specific ethtool statistics counter and a generic
> "tx_dropped" counter in ndo_get_stats64.

Any chance we should also report that back to the qdisc to have 
a standard way of querying from user space? Qdisc offload supports
stats in general, it shouldn't be an issue, and the stat seems generic
enough, no?