* valdis.kletni...@vt.edu <valdis.kletni...@vt.edu> wrote:
> On Fri, 25 Jan 2013 09:11:01 -0500, ling.ma.prog...@gmail.com said:
>
> > Based on above reasons, we compiled linux kernel 3.6.9 with O2 and Os
> > respectively. The results show Os improve performance netperf 4.8%,
> > 2.7% for volano as below
>
> Am I allowed to NAK this? What the numbers given so far
> *actually* show is 4.8% more instructions executed, *not* 4.8%
> better performance.
cycles and elapsed time is down in both tests - the speedup
seems statistically a wash in the first test and significant for
the second workload.
the instruction count might be an artifact of byte wise versus
word wise REP; MOV.
> I'm having a *very* hard time convincing myself that what
> we're seeing isn't simply the expected behavior of loops *not*
> being unrolled and similar non-optimizations done by -Os, so
> more instructions get executed to do the same amount of work.
>
> Rather than "run for 10 seconds and count instructions", can
> we "run for 50,000 syscalls and count clock time" or similar
> that shows an *actual* improvement?
Look at the numbers, it counts a whole lot of other things as
well beyond instructions - elapsed time being the most important
one.
But more numbers never hurt.
Thanks,
Ingo
--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majord...@vger.kernel.org
More majordomo info at http://vger.kernel.org/majordomo-info.html
Please read the FAQ at http://www.tux.org/lkml/
