Compile with -fno-omit-frame-pointer on x86_64?

[Jakub Jelinek]

On Wed, Nov 03, 2010 at 03:20:59PM -0400, Owen Taylor wrote:
> On Wed, 2010-11-03 at 19:58 +0100, Jakub Jelinek wrote:
> > On Wed, Nov 03, 2010 at 02:48:12PM -0400, Owen Taylor wrote:

> > Instead of this, which really is a big performance penalty. 
> 
> Do you have a sense of the quantification of "big" here? I know in
> compiler terms, 1% is big, but we're no where close to wringing the last
> 1% out of overall Fedora performance. If you create a sufficiently
> complex system, there's lots of "stupid" stuff going on. And you can't
> find the stupid stuff without appropriate tools.

The last numbers I was pointed at for x86_64 were 4% slowdown, which
really is a lot and it takes several years to achieve that improvement on the
compiler side.

> It seems like if it was that easy, it would have happened and we'd have
> a solution in the upstream kernel...

I think we had one in the upstream kernel for some time, then Linus just
didn't like to see it needing too many bugfixes needed for it and nuked it.

> (One thing that definitely makes things tricky is paging in debuginfo. I
> think I saw a discussion somewhere that systemtap preemptively was
> paging in all debuginfo for traced modules. That's tricky in systemwide

Yeah, systemtap does that (and has that in kernel unwinder for userspace).

	Jakub