netdev - Re: [PATCH 2.6.19] AT91RM9200 Ethernet update 3

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Message-Id: <1165303792.12510.55.camel@fuzzie.sanpeople.com>
Date:	05 Dec 2006 09:29:52 +0200
From:	Andrew Victor <andrew@...people.com>
To:	Stephen Hemminger <shemminger@...l.org>
Cc:	netdev@...r.kernel.org, jgarzik@...ox.com
Subject: Re: [PATCH 2.6.19] AT91RM9200 Ethernet update 3

hi Stephen,

> Use netdev_alloc_skb instead. It sets skb->dev so you don't have to.

netdev_alloc_skb() seems to cause 2 function calls [__netdev_alloc_skb()
and __alloc_skb()], instead of just 1 for the dev_alloc_skb() case.
It might be more efficient if the driver manually sets skb->dev.

> Setting skb->len is redundant since that is what skb_put() does.

That's why that line is being removed.

> It would be best if you didn't have to copy data at all and could
> receive directly into the skb.

Probably, but then we'd need to worry about DMA and cache-aligned
skb's.  We'd also need to always allocate maximum-sized skb's;  and that
might be an issue since the AT91RM9200 is mainly used in embedded
devices where the amount of RAM can be limited.

> The existing code will cause poor realtime
> performance since the driver is copying received data with IRQ's disabled.

Only lower-priority interrupts should be disabled.

Regards,
  Andrew Victor

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