netdev - Re: [PATCH 09/12] net: mediatek: increase watchdog

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Date:	Mon, 6 Jun 2016 14:21:32 +0200
From:	Andrew Lunn <andrew@...n.ch>
To:	John Crispin <john@...ozen.org>
Cc:	Sean Wang <keyhaede@...il.com>, netdev@...r.kernel.org,
	linux-kernel@...r.kernel.org, linux-mediatek@...ts.infradead.org,
	"David S. Miller" <davem@...emloft.net>,
	Felix Fietkau <nbd@....name>
Subject: Re: [PATCH 09/12] net: mediatek: increase watchdog_timeo

> Hi Andrew,
> 
> it is waiting for the watchdog to trigger :-) TBH the 1s seems to be too
> short to for the dma ring length to be flushed and i had to pick some
> value and 5 is used most places.
> 
> it really depends on the amount of packets in the queue, their length
> and the mac setting. the timeout needs to be large enough that it would
> not trigger incorrectly even if the mac is on 10mbit half duplex and all
> frames in the queue were maximum size.

So you are saying there is 5 seconds worth of traffic in the transmit ring.

As a general point, not specific to this driver, is that wise? Isn't
that really bad buffer bloat?

I just wondered what happened to cause it to have 5 seconds worth of
traffic in the transmit ring. Did downstream signal a pause?  But i
thought the byte queue limit was designed to prevent a big backlog in
the transmit queue? At 10/Half, is it not reacting fast enough?  Since
it is half duplex, do you have a lot of traffic coming the other way
and something is not being fair at distributing up and down traffic?

I'm just wondering if by increasing the watchdog to 5 seconds, you are
just hiding a problem.

    Andrew