netdev - Re: arm: Optimization for ethernet MAC handling at91

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Message-ID: <4B4CCC7B.8040609@gmail.com>
Date:	Tue, 12 Jan 2010 20:24:43 +0100
From:	Eric Dumazet <eric.dumazet@...il.com>
To:	James Kosin <JKosin@...comgrp.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

Le 12/01/2010 20:03, James Kosin a écrit :
> 
> Scratch that.  The interrupt doesn't queue up or send another packet directly.  So, it wouldn't help on performance here.  But, may in other implementations that queue/transmit packets in the ISR.  At least in the case where the transmitter is limited to one.
> 

It could, at least on SMP. tx completion wakes a blocked sender, while
this cpu continue with RX handling (possibly expensive)

But even on UP, doing tx completion before rx handling allows
a better reuse of skb just freed (and partly present in cpu cache, if available).

Start of IRQ

1) tx completion
    -> free a skb

2) rx handling:
    -> allocate an skb, kmalloc() reuses previous one, still in cpu cache.

End of IRQ
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