Re: [patch 0/9] mutex subsystem, -V4

[Christoph Hellwig <hch@infradead.org>]

On Thu, Dec 22, 2005 at 12:41:47PM +0100, Ingo Molnar wrote:
> this is the -V4 of the mutex subsystem patch-queue. It consists of the 
> following patches:
> 
>   add-atomic-xchg.patch
>   add-atomic-call-func-i386.patch
>   add-atomic-call-func-x86_64.patch
>   add-atomic-call-wrappers-rest.patch
>   mutex-core.patch
>   mutex-switch-arm-to-xchg.patch
>   mutex-debug.patch
>   mutex-debug-more.patch
>   xfs-mutex-namespace-collision-fix.patch
> 
> the patches are against Linus' latest GIT tree, and they should work 
> fine on every Linux architecture.
> 
> Changes since -V3:
> 
> - imlemented an atomic_xchg() based mutex implementation. It integrated
>   pretty nicely into the generic code, and most of the code is still
>   shared.
> 
> - added __ARCH_WANT_XCHG_BASED_ATOMICS: if an architecture defines 
>   this then the generic mutex code will switch to the atomic_xchg() 
>   implementation.
> 
>   This should be conceptually equivalent to the variant Nicolas Pitre 
>   posted - Nicolas, could you check out this one? It's much easier to 
>   provide this in the generic implementation, and the code ends up 
>   looking cleaner.
> 
> - eliminated ARCH_IMPLEMENTS_MUTEX_FASTPATH: there's no need for 
>   architectures to override the generic code anymore, with the 
>   introduction of __ARCH_WANT_XCHG_BASED_ATOMICS.
> 
> - ARM: enable __ARCH_WANT_XCHG_BASED_ATOMICS.

I must admit I really really hat __ARCH_ stuff if we can avoid it.
An <asm/mutex.h> that usually includes two asm-generic variants is probably
a much better choice.

Actually just havign asm/mutex.h implement the faspath per-arch and get
rid of all the oddball atomic.h additions would be even better.  While
this means we need per-arch code it also means the code is a lot easier
understandable, and we don't add odd public APIs.