Messages in this thread | | | Date | Wed, 4 Feb 2009 22:29:13 +0100 | From | Ingo Molnar <> | Subject | Re: mmotm 2009-02-02-17-12 uploaded (x86/nopmd etc.) |
| |
* Andrew Morton <akpm@linux-foundation.org> wrote:
> On Wed, 4 Feb 2009 21:08:46 +0100 > Ingo Molnar <mingo@elte.hu> wrote: > > > > > * Andrew Morton <akpm@linux-foundation.org> wrote: > > > > > > > This is getting painful. > > > > > > > > the include file spaghetti is ... interesting there, and it's historic. > > > > > > > > I could blame it on highmem, PAE or paravirt - but i'll only blame it on > > > > paravirt for now because those developers are still around! ;-) > > > > > > > > Jeremy, any ideas how to reduce the historic dependency mess in that area? > > > > I think we should go on three routes at once: > > > > > > > > - agressive splitup and separation of type definitions from method > > > > declaration (+ inline definitions). The spinlock_types.h / spinlock.h > > > > splitup was really nice in solving such dependency problems. > > > > > > I like this one. The mixing up of declare-something with use-something > > > is often the source of our woes. > > > > yes. I mapped this problem area once and this is how the include file > > spaghetti gets generated in practice: > > > > - type A gets declared > > - type A gets _used_ in the same file in an inline method, BUT, > > > > that usage also brings in instantiated use of type X1, X2 and X3. > > > > if all types are declared like that everywhere, it can be seen (and it's a > > mathematical certainty) that the only conflict-free way of doing this is to: > > > > - initially add random #include lines to bring in type X1, X2 and X3. > > Which brings in recursive dependencies from those X1 X2 and X3 files. > > > > - when the stuff hits the fan then folks are in a big mess already and > > only a deep restructuring could gets them out of it - which they rarely > > do in an iterative environment. So they work it around iteratively: > > instead of new nice inline methods [which we really prefer] they delay > > all the 'usage' instantiation to .c file via the use of CPP macros > > [which we hate because they hide bugs and cause bugs]. > > None of which would happen if we didn't also have an inlining fetish.
inlining is a nice and convenient tool that helps us do better code in many cases. It has this long-term dependency-deteriorating effect though.
Ingo
| |