Re: Performance of function calls of SH?(Fw: [RFC][selinux] Tuning SELinux permission check

[Yuichi N. <yn...@hi...>]

On Mon, 10 Sep 2007 18:35:28 +0900
Paul Mundt wrote:
> On Mon, Sep 10, 2007 at 06:19:12PM +0900, Yuichi Nakamura wrote:
> > 
> > On Mon, 10 Sep 2007 16:09:10 +0900
> > Paul Mundt wrote:
> > > What optimization levels are you using to compile the kernel? Try with
> > > and without -Os to see if there's a measurable impact. From the sounds of
> > > it you're still going to have to do the manual inlining work if there's
> > > no change in the common case, at least.
> > I was using -O2.
> > I now compiled with -Os and compared.
> > 
> > lmbench result for SH(SH4, SH7751R), kernel 2.6.22
> >                SELinux(gcc4.2.1 -O2)  SELinux(gcc 4.2.1 -Os)
> > Simple read     6.03                  4.24
> > Simple write    5.92                  3.88
> > Very strange. -Os is better.
> > # I tried twice to make sure.
> > 
> The inlining semantics for both of these are a bit different, but it's
> curious that -Os resulted in faster code given that it has a tendency to
> try and keep things that are referenced more than once out-of-line.
> 
> >                No SELinux(gcc4.2.1 -O2)  No SELinux(gcc 4.2.1 -Os)
> > Simple read    2.36                       2.45
> > Simple write   2.06                       2.08
> > Without SELinux, O2 is a little better.
> > 
> What about bumping this to -O3? It seems like the compiler is at least
> able to produce good code, the main issue is just the optimization level
> and inlining semantics at this point. 
Thanks for reply, again.

I tried -O3.
Kernel panic on gcc 3.4.5.
On 4.2.1 it booted.

SELinux(gcc 4.2.1 -O3)
Simple read     4.53
Simple write    4.23

Better than O2, but Os is better.

I tried manual inlining with -Os, 
SELinux(gcc 4.2.1 -Os) + manual inlining
Simple read     3.64
Simple write    3.34
It is still effective.

> On the other hand, with newer
> compilers we really should be using -Os as the default anyways (this is
> also the default for most ARM boards), it hasn't been a problem for some
> time.
Does it mean, "most people are using -Os now" ?

-- 
Yuichi Nakamura
Hitachi Software Engineering Co., Ltd.
Japan SELinux Users Group(JSELUG): http://www.selinux.gr.jp/
SELinux Policy Editor: http://seedit.sourceforge.net/