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    SubjectRe: [patch 3/3] mutex subsystem: move the core to the new atomic helpers
    On Thu, Dec 22, 2005 at 12:12:18AM +0100, Ingo Molnar wrote:
    > * Nicolas Pitre <> wrote:
    > > This patch moves the core mutex code over to the atomic helpers from
    > > previous patch. There is no change for i386 and x86_64, except for
    > > the forced unlock state that is now done outside the spinlock (doing
    > > so doesn't matter since another CPU could have locked the mutex right
    > > away even if it was unlocked inside the spinlock). This however
    > > brings great improvements on ARM for example.
    > i'm wondering how much difference it makes on ARM - could you show us
    > the before and after disassembly of the fastpath, to see the
    > improvement?
    > your patches look OK to me, only one small detail sticks out: i'd
    > suggest to rename the atomic_*_contended macros to be arch_mutex_*_...,
    > i dont think any other code can make use of it. Also, it would be nice
    > to see the actual ARM patches as well, which make use of the new
    > infrastructure.

    I'm personally a little worried about the recent proliferation of

    My take on atomic_* functions has always been: a "sensible" arch [1]
    implements the functionality in a single atomic instruction and this
    simply exposes that instruction at the C level which otherwise lacks
    appropriate semantics.

    So functions like atomic_dec_call_if_negative seem a) excessively
    special purpose b) not fundamental in the
    ought-to-be-a-single-instruction sense c) a bit out of place in the in
    the atomic_* set. These might even encourage people to roll their own
    special-purpose locking primitives and we have way too many of those

    [1] In Linus' famous sense of what an ideal architecture should look like

    Mathematics is the supreme nostalgia of our time.
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