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    Subject[PATCH 05/15] lib: percpu_count_sum_signed()
    Provide an accurate version of percpu_counter_read.

    Should we go and replace the current use of percpu_counter_sum()
    with percpu_counter_sum_positive(), and call this new primitive
    percpu_counter_sum() instead?

    Signed-off-by: Peter Zijlstra <a.p.zijlstra@chello.nl>
    ---
    include/linux/percpu_counter.h | 18 +++++++++++++++++-
    lib/percpu_counter.c | 6 +++---
    2 files changed, 20 insertions(+), 4 deletions(-)

    Index: linux-2.6/include/linux/percpu_counter.h
    ===================================================================
    --- linux-2.6.orig/include/linux/percpu_counter.h 2007-05-02 19:43:34.000000000 +0200
    +++ linux-2.6/include/linux/percpu_counter.h 2007-05-04 09:42:47.000000000 +0200
    @@ -41,7 +41,18 @@ static inline void percpu_counter_destro
    void percpu_counter_set(struct percpu_counter *fbc, s64 amount);
    void __percpu_counter_mod(struct percpu_counter *fbc, s32 amount, s32 batch);
    void __percpu_counter_mod64(struct percpu_counter *fbc, s64 amount, s32 batch);
    -s64 percpu_counter_sum(struct percpu_counter *fbc);
    +s64 __percpu_counter_sum(struct percpu_counter *fbc);
    +
    +static inline s64 percpu_counter_sum(struct percpu_counter *fbc)
    +{
    + s64 ret = __percpu_counter_sum(fbc);
    + return ret < 0 ? 0 : ret;
    +}
    +
    +static inline s64 percpu_counter_sum_signed(struct percpu_counter *fbc)
    +{
    + return __percpu_counter_sum(fbc);
    +}

    static inline void percpu_counter_mod(struct percpu_counter *fbc, s32 amount)
    {
    @@ -130,6 +141,11 @@ static inline s64 percpu_counter_sum(str
    return percpu_counter_read_positive(fbc);
    }

    +static inline s64 percpu_counter_sum_signed(struct percpu_counter *fbc)
    +{
    + return fbc->count;
    +}
    +
    #endif /* CONFIG_SMP */

    static inline void percpu_counter_inc(struct percpu_counter *fbc)
    Index: linux-2.6/lib/percpu_counter.c
    ===================================================================
    --- linux-2.6.orig/lib/percpu_counter.c 2007-05-02 19:43:34.000000000 +0200
    +++ linux-2.6/lib/percpu_counter.c 2007-05-04 09:38:36.000000000 +0200
    @@ -62,7 +62,7 @@ EXPORT_SYMBOL(__percpu_counter_mod64);
    * Add up all the per-cpu counts, return the result. This is a more accurate
    * but much slower version of percpu_counter_read_positive()
    */
    -s64 percpu_counter_sum(struct percpu_counter *fbc)
    +s64 __percpu_counter_sum(struct percpu_counter *fbc)
    {
    s64 ret;
    int cpu;
    @@ -74,6 +74,6 @@ s64 percpu_counter_sum(struct percpu_cou
    ret += *pcount;
    }
    spin_unlock(&fbc->lock);
    - return ret < 0 ? 0 : ret;
    + return ret;
    }
    -EXPORT_SYMBOL(percpu_counter_sum);
    +EXPORT_SYMBOL(__percpu_counter_sum);
    --

    -
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