[vortex] Question about linux 3com driver

[Donald Becker]

On Wed, 10 Jul 2002, Raymond Jennings wrote:

> I have a question about your driver for 3Com for 905c & 905cx cards.  I
> have been using these cards because the driver supports the NETIF_F_SG
> option as well as checksum offloading.
> 
> I found through testing that this card/driver does not support zero-copy
> for highmem pages.

It's not clear that there is a performance advantage to doing so:
locking and remapping pages is a very expensive operation on SMPs, and
can easily cost more than just the copying into always-PCI-accessable
skbuff.

> I'm curious about this comment.  Isn't it the case that zero-copy could
> still work with CONFIG_HIGHMEM?  The only catch would be for skbuff's that
> contain highmem pages the skbuff would have to be "linearized" which the
> network stack does automatically (at least as of 2.4.16 possibly earlier.)


-- 
Donald Becker				becker@scyld.com
Scyld Computing Corporation		http://www.scyld.com
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