* Nick Piggin <[email protected]> wrote:
> >+#ifdef __HAVE_ARCH_CMPXCHG
> >+ if (likely(atomic_cmpxchg(count, 1, 0)) == 1)
> >+ return 1;
> >+ return 0;
> >+#else
> >+ return fail_fn(count);
> >+#endif
> >+}
>
> asm-i386 version I think really should just use atomic_cmpxchg
> unconditionally, because otherwise an i386 compatible kernel will not
> use cmpxchg even when running on 486+ (not sure how important that is
> these days, but still...).
yeah. This code predates the generic-atomic-cmpxchg code. (Feel free to
review all __HAVE_ARCH_CMPXCHG users after this goes in, and remove
__HAVE_ARCH_CMPXCHG altogether with a CONFIG_ flag.)
but ... the spinlock based variant is quite likely faster (on i386) than
generic-cmpxchg. Couldnt we introduce a new API, something along the
lines of:
atomic_cmpxchg_lock(&count, &lock->wait_lock);
and if the cmpxchg fails, it would hold the spinlock? The cmpxchg
semantics could be guaranteed by the spinlock. (because it is 'global'
for that particular critical section)
Ingo
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