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Date:	Mon, 21 Apr 2014 12:55:12 -0700
From:	Florian Fainelli <>
To:	David Miller <>
Cc:	netdev <>
Subject: Re: [PATCH net-next 2/4] net: bcmgenet: add support for ethtool tx-frames

2014-04-21 12:17 GMT-07:00 David Miller <>:
> From: Florian Fainelli <>
> Date: Mon, 21 Apr 2014 08:45:22 -0700
>> Configuring the ethtool tx-frames property, which translates into N
>> packets before a TX interrupt is the simplest configuration scheme
>> because it requires no locking neither at the softare nor hardware
>> level, and is completely indepedent from the link speed. Since ethtool
>> does not allow per-tx queue coalescing parameters, we apply the same
>> setting to any transmit queue.
>> We can no longer enable the BDONE/PDONE interrupts as those would fire
>> for each packet/buffer received, which would defeat the MBDONE interrupt
>> purpose. The MBDONE interrupt is guaranteed to correspond to a
>> PDONE/BDONE interrupt when the threshold is set to 1.
>> Signed-off-by: Florian Fainelli <>
> Does the MBDONE scheme have a timeout?
> For example if you ask for a MBDONE setting where N=4, if only 2 packets
> arrive will you get an interrupt or will it wait for 2 more to arrive
> no matter what?

There is no configurable timeout for the transmit DMA engine (receive
does have one), but we do get a ring empty interrupt as soon as the
transmit path has completed the packets, so the MBDONE interrupt cause
always makes us run the TX reclaim logic.

> If a timeout doesn't exist, you cannot use this.
> I'm very pessimistic because I see no inspection of the timeout
> parameter passed into the ethtool commands.  And in fact if the
> timeout does exist, and is fixed, you should error on non-zero
> values specified in the timeout field(s).
> So no matter what the situation is wrt. timeouts, this series needs
> either change or be completely tossed.

I will rework it, thanks for your feedback.
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