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

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Message-ID: <20121012180411.GA26245@liondog.tnic>
Date:	Fri, 12 Oct 2012 20:04:11 +0200
From:	Borislav Petkov <bp@...en8.de>
To:	"Ma, Ling" <ling.ma@...el.com>
Cc:	Konrad Rzeszutek Wilk <konrad@...nel.org>,
	"mingo@...e.hu" <mingo@...e.hu>, "hpa@...or.com" <hpa@...or.com>,
	"tglx@...utronix.de" <tglx@...utronix.de>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"iant@...gle.com" <iant@...gle.com>
Subject: Re: [PATCH RFC 2/2] [x86] Optimize copy_page by re-arranging
 instruction sequence and saving register

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.
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