Zerocopy implementation issues

From: Russell King (
Date: Sat Apr 28 2001 - 18:52:06 EST


Can someone please explain to me the rationale behind the zerocopy
implementation that has appeared in 2.4.4 please?

The reason I ask is that even on x86, it seems to me to be extremely
silly to have the expense of doing unaligned checksumming for the gain
of zerocopy.

Just think - if you did checksumming on aligned word boundaries you
could be far faster!

(Yes, you guessed it, its broken on ARM, and is going to make the
networking layer pig slow if we keep the current implementation as
it stands due to the phenominal amount of exceptions it _will_
generate - 1 exception per word in a packet).

I'm still investigating the source of the networking corruptions I'm
seeing, but its looking like the above is the reason (data is being
corrupted on TCP send).

Russell King (                The developer of ARM Linux

- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to More majordomo info at Please read the FAQ at

This archive was generated by hypermail 2b29 : Mon Apr 30 2001 - 21:00:21 EST