Re: gcc 2.7.1

Henrik Olsen (henrik@iaeste.dk)
Thu, 6 Aug 1998 03:34:54 +0000 ( )

On Wed, 5 Aug 1998, Linus Torvalds wrote:
> On Wed, 5 Aug 1998, Etienne Lorrain wrote:
> >
> > Maybe it is time to upgrade to gcc-2.7.3, so that this patch could
> > be applied in the main stream :
>
> Do you have numbers for the effect of "-fno-strength-reduce"? Back when I
> added it I couldn't see any difference at all to any benchmarks, so I've
> had no real incentive to even try to remove it.
>
> Does anybody have any numbers that show that it actually matters for the
> kernel (I know it matters a lot for some other things, but I'm looking for
> something that really makes a difference in kernel-land)?
>
> Linus

Just tested the effect of -fno-strength-reduce on the standard Linux
benchmark, compiling the kernel, measuring with time:)

With -fno-strength-reduce:
just after reboot:
358.60user 20.50system 6:45.00elapsed 93%CPU

repeated immediately (all source in cache):
357.74user 20.97system 6:23.29elapsed 98%CPU

without -fno-strength-reduce:
just after reboot:
357.38user 21.35system 6:44.09elapsed 93%CPU

repeated immediately (all source in cache):
358.75user 19.57system 6:23.98elapsed 98%CPU

It looks like, for "normal" work, the difference is virtually nonexistent,
and totally overshadowed by the effects of usage patterns, resulting in
any actual effect being below the noise level of general measures.

HTH,

-- 
Henrik Olsen,   CNA, working on CNE.
URL=http://www.iaeste.dk/~henrik/
Get the rest there.




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