Re: [UPDATE] Fresh zerocopy patch on

From: Malcolm Beattie (
Date: Thu Feb 01 2001 - 06:20:15 EST

David S. Miller writes:
> Malcolm Beattie writes:
> > David S. Miller writes:
> > >
> > > At the usual place:
> > >
> > >
> >
> > Hmm, disappointing results here; maybe I've missed something.
> As discussed elsewhere there is a %10 to %15 performance hit for
> normal write()'s done with the new code.
> If you do your testing using sendfile() as the data source, you'll
> results ought to be wildly different and more encouraging.

I did say that the ftp test used sendfile() as the data source and
it dropped from 86 MB/s to 62 MB/s. Alexey has mailed me suggesting
the problem may be that netfilter is turned on. It is indeed turned
on in both the 2.4.1 config and the 2.4.1+zc config but maybe it has
a far higher detrimental effect in the zerocopy case. I'm currently
building new non-netfilter kernels and I'll go through the exercise
again. I'm confident I'll end up being impressed with the numbers
even if it takes some tweaking to get there :-)


Malcolm Beattie <>
Unix Systems Programmer
Oxford University Computing Services
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