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SubjectRe: The Kommunity vs. Dick Johnson
Marc Lehmann <pcg@goof.com> wrote:
> Actually, I get:

> Change : 1.86 times faster

> with -O6 (pgcc), and

> Change : 0.54 times faster

Marc P-II 333 pgcc -O2 1.86 times faster
Marc P-II 333 pgcc -O6 -funroll-all-loops 0.54 times faster
Erik PPro 180 gcc-2.7.2.3 -O2 13149 2.5 times faster
Erik PPro 180 gcc-2.7.2.3 -O6 13261 2.5 times faster
Erik PPro 180 gcc-2.7.2.3 -O6 -funroll-all-loops 14125 1.45 times faster

Using the i386 checksum code from 2.0.34/2.1.107 instead of the
C code:

Erik PPro 180 gcc-2.7.2.3 -O2 13354 1.29 times faster
Erik PPro 180 gcc-2.7.2.3 -O6 -funroll-all-loops 14778 0.08 times faster

(You can get the code for this from
http://www.image.dk/~ehcorry/linux/chksum.c It slots into
the files Richard distributed.)

I conclude that -funroll-all-loops is ruining the test,
probably optimising the timing loop out of existence.
Either that, or it is unrolling a loop inside an inline
asm statement, which I don't believe.

Also, on a PPro, Richard's code is probably 1.29 times
faster than what we already have.

This whole discussion has been a little unfocused.
Richard seems to think he is up against people who don't
like assembler, but the real kernel developers have
nothing against assembler in places where it is useful.
The proof is that the routine he chose as an example
is already written in assembler on most architectures.
This seems to have been missed by most of the people who
have attacked Richard.

Now that Richard has proven that he is a good assembler
hacker, it would be nice if he (or someone else) made
a patch, so we all got more out of it than a warm glow
by proxy. Of course one will have to adapt his code so
it does partial checksums of fragments and also does the
copy-and-checksum tricks, and it remains to be seen whether
the benefits are still visible in real usage (or at least
in lmbench) and on x86 processors that are non-Intel

--
"It's not so much an afterlife, more a sort of apres-vie." --DNA
--
Erik Corry erik@arbat.com Ceterum censeo, Microsoftem esse delendam!

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