lkml.org 
[lkml]   [2000]   [Sep]   [2]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
/
Date
From
SubjectRe: zero-copy TCP
On Sat, Sep 02, 2000 at 04:28:18PM -0600, Jeff V. Merkey wrote:
>
>
> Alan Cox wrote:
> >
> > We dont copy for checksumming. We fold the single user space copy and the
> > checksum operation into one path, because on any modern CPU it costs precisely
> > the same to copy as to copy/checksum.
>
> You stated in an earlier message you copied the data when you caclulated
> the TCPIP checksum? No you say you don't. Perhaps I misunderstood.

Linux always does a single copy for TCP, and the checksum is folded into
that. Doing just the checksum alone wouldn't be much less costly.

[Note this is only true for 2.4 in the fast path, 2.2 RX usually does
checksum and copy-to-user separated, unless you have hardware RX checksumming

For TX we always do a single copy checksum out of user space or out of the
page cache when you use sendfile or mmap]


-Andi
-
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@vger.kernel.org
Please read the FAQ at http://www.tux.org/lkml/

\
 
 \ /
  Last update: 2005-03-22 12:38    [from the cache]
©2003-2011 Jasper Spaans