Re: [ANNOUNCE] ktimers subsystem

Daniel Walker
2005-09-24T16:51:52Z

On Sat, 2005-09-24 at 15:56 +0200, Thomas Gleixner wrote:
> On Sat, 2005-09-24 at 12:35 +0200, Roman Zippel wrote:
> > Hi,
> >
> > On Sat, 24 Sep 2005, Ingo Molnar wrote:
> >
> > > > Anyway, the biggest cost is the conversion from/to the 64bit ns value
> > > > [...]
> > >
> > > Where do you get that notion from? Have you personally measured the
> > > performance and code size impact of it? If yes, would you mind to share
> > > the resulting data with us?
> > >
> > > Our data is that the use of 64-bit nsec_t significantly reduces the size
> > > of a representative piece of code (object size in bytes):
> > >
> > > AMD64 I386 ARM PPC32 M68K
> > > nsec_t_ops 226 284 252 428 206
> > > timespec_ops 412 324 448 640 342
> > >
> > > i.e. a ~40% size reduction when going to nsec_t on m68k, in that
> > > particular function. Even larger, ~45% code size reduction on a true
> > > 64-bit platform.
> >
> > Without any source these numbers are not verifiable. You don't even
> > mention here what that "representative piece of code" is...

These numbers are misleading .. Doing a total code comparison shows that
a 2.6.14-rc2+ktimers kernel is slightly bigger than a vanilla 2.6.14-rc2
kernel (gcc 4.0, defconfig) .. So your argument that "small is faster"
must mean ktimers is slower, or at least not faster ..

Making a speed argument based on code size doesn't make much sense to
me, if it's actually faster then show that it's faster.

Daniel