linux-kernel - RE: arm: Optimization for ethernet MAC handling at91

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Date:	Tue, 12 Jan 2010 12:51:57 -0500
From:	"James Kosin" <JKosin@...comgrp.com>
To:	"Eric Dumazet" <eric.dumazet@...il.com>
Cc:	<linux-kernel@...r.kernel.org>,
	"Linux Netdev List" <netdev@...r.kernel.org>
Subject: RE: arm: Optimization for ethernet MAC handling at91_ether.c

On 1/12/2010 11:40 AM, Eric Dumazet wrote:
> CC to netdev
> 
> Le 12/01/2010 16:39, James Kosin a écrit :
>> Everyone,
>>
>> Since, a AT91_EMAC_TUND only happens when the transmitter is unable to
>> transfer the frame in time for a frame to be sent.  It makes sense to
>> RETRY the packet in this condition in the ISR.
>> Or would this overcomplicate a simple task?
>>                 ... see below ...
>>
> ...
> 
>>
>> ...
>> I do know there needs to be a bit more code then to handle the
>> successful case below this; but, this is enough to understand what I am
>> talking about.  The UNDERRUN error should happen infrequently and in
>> ideal circumstances not happen at all.
>>  
> 
> 
> If this happens once in a while, why do you want driver to retry the transmit ?

(a)  It would improve performance by allowing the ISR to handle the re-transmit in this case.
(b)  It would help in the case of small glitches that may happen from external SDRAM without taxing the polling required to handle the re-transmit of the packet... ie: overhead required to re-queue and initiate a packet delivery... since the packet is already scheduled for delivery now.

James
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