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    SubjectRe: [RFC local_t removal V1 0/4] Remove local_t
    * Christoph Lameter (cl@linux-foundation.org) wrote:
    > On Tue, 5 Jan 2010, Mathieu Desnoyers wrote:
    >
    > > Yes, removing the local_t type could make sense. However, local_t maps
    > > to a volatile long, not just "long". Secondly, I am concerned about the
    > > fact that the patch you propose:
    >
    > Volatile is discouraged as far as I can tell.

    If you want to ensure that a simple variable assignment or read
    (local_set, local_read) are not performed piecewise by the compiler
    which can cause odd effects when shared with interrupt handlers, this
    will however be necessary.


    >
    > > - does not create the primitives I use in lttng
    > > - only deals with x8
    >
    > As I said its an RFC. This provides all the functionality you need
    > through. The rest is sugar coating.

    OK

    >
    > > In lttng (which is out of tree, but widely used), I need the equivalent
    > > of:
    > >
    > > local_read
    > > local_set
    > > local_add
    > > local_cmpxchg
    > > local_add_return
    > > local_inc
    >
    > Please read the patch! This is all provided. add_local_return in the RFC
    > provides what is needed to replace local_add, local_inc. We can add these
    > explicitly.
    >
    > local_cmpxchg replacement is already in there in the form of
    > cmpxchg_local().
    >
    > > The approach of just doing the x86 implementation and leaving all the
    > > other architectures "for later" with a slow/non atomic generic fallback
    > > is, imho, a no-go, given that some people (myself, actually) already
    > > took the time to go through all the kernel architectures to create the
    > > optimized local.h headers. Basically, you are destroying all that work,
    > > asking for it to be done all over again.
    >
    > AS I said this is an RFC. I can easily generate all these things from the
    > existing local.hs for the architectures.
    >
    > > I therefore argue that we should keep local.h as-is as long as the
    > > replacement lacks the wide architecture support and primitive variety
    > > found in local.h.
    >
    > Cool down and please review the patch.

    OK :)

    Mathieu
    >
    >

    --
    Mathieu Desnoyers
    OpenPGP key fingerprint: 8CD5 52C3 8E3C 4140 715F BA06 3F25 A8FE 3BAE 9A68


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