Re: TCP Checksum offload in 2.4.19

From: Nivedita Singhvi (niv@us.ibm.com)
Date: Thu Sep 05 2002 - 11:58:48 EST


> Instead of making changes to my application to use
> sendfile(..), is it possible for me to enable zerocopy
> in 2.4.19 kernel (using a patch or something) so that
> tx checksum can be offloaded to the h/w for every TCP
> packet?

tx checksum offload and zerocopy are two different things.
checksum offload doesnt require zerocopy enabled. It can
be done for both sendmsg() and sendfile() code paths, but
provides significant gain only in the sendfile() code path
which has eliminated the expensive user->kernel copy. In
the sendmsg() case, the checksum is computed while doing
the copy operation.

Doing zerocopy on the sendmsg() code path is nontrivial
and the end result is really sendfile().

thanks,
Nivedita

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