Re: [PATCH RFC 2/2] [x86] Optimize copy_page by re-arranging instruction sequence and saving register

[Borislav Petkov <bp@alien8.de>]

On Fri, Oct 12, 2012 at 09:07:43AM +0000, Ma, Ling wrote:
> > > > So is that also true for AMD CPUs?
> > > Although Bulldozer put 32byte instruction into decoupled 16byte entry
> > > buffers, it still decode 4 instructions per cycle, so 4 instructions
> > > will be fed into execution unit and
> > > 2 loads ,1 write will be issued per cycle.
> > 
> > I'd be very interested with what benchmarks are you seeing that perf
> > improvement on Atom and who knows, maybe I could find time to run them
> > on Bulldozer and see how your patch behaves there :-).M
> I use another benchmark from gcc, there are many code, and extract
> one simple benchmark, you may use it to test (cc -o copy_page
> copy_page.c), my initial result shows new copy page version is still
> better on bulldozer machine, because the machine is first release,
> please verify result. And CC to Ian.

Right, so benchmark shows around 20% speedup on Bulldozer but this is a
microbenchmark and before pursue this further, we need to verify whether
this brings any palpable speedup with a real benchmark, I don't know,
kernbench, netbench, whatever. Even something as boring as kernel build.
And probably check for perf regressions on the rest of the uarches.

Thanks.

-- 
Regards/Gruss,
    Boris.