Hi Jesse,
Thanks for your reply. I still have two questions about packet splittng:
Question one: when e1000 does packet splitting, it seems packet data buffer
is splitted into three parts, but how does e1000 decide how many parts
needed to be splitted?
Question two: It seems e1000 does not split those parts into equal size, why
not choose equal size for each splitted part?
Regards,
John
From: Jesse Brandeburg <[EMAIL PROTECTED]>
To: John Smith <[EMAIL PROTECTED]>
CC: netdev@vger.kernel.org
Subject: Re: What is packet split? Same as copybreak?
Date: Sat, 21 Jan 2006 23:49:04 -0800
On 1/20/06, John Smith <[EMAIL PROTECTED]> wrote:
> Hi,
>
> I just have some questions about the packet splitting which is supported
by
> some PCI-express platforms. It seems the packet data buffer part (header
and
> payload) is splitted into several parts and stored into different
buffers
> while PCI-X NIC use 2K data buffer for every packet.
sounds like you're talking about e1000, so I'll answer.
> My question is: what is the purpose of this packet splitting? It seems
each
> splitted part has different size, why not choose a uniform size for each
> part?
the major purpose is to have the data aligned to a 4k boundary, and to
have a seperate allocation for the network header. It really seems to
help most for decreasing cpu utilization, AFAICT.
> It seems it serve the same purpose as copybreak. Can anyone please me
give
> some more hints.
I believe it does serve much the same purpose, but copybreak optimizes
receive socket buffer utilization (thanks to davem for pointing that
out) esp if a dma device allocates a large amount of space (say for
jumbo frame reception) and dev_alloc_skb forces an increase in
allocation size to the next power of 2.
conceiveably it could give you some efficiency due to multiple TCP/IP
header buffers in the same page.
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