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    SubjectRe: [PATCH 2/8] Basic zcache functionality
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    Date
    Le vendredi 16 juillet 2010 à 18:07 +0530, Nitin Gupta a écrit :

    > This particular patch implemets basic functionality only:
    > +static u64 zcache_get_stat(struct zcache_pool *zpool,
    > + enum zcache_pool_stats_index idx)
    > +{
    > + int cpu;
    > + s64 val = 0;
    > +
    > + for_each_possible_cpu(cpu) {
    > + unsigned int start;
    > + struct zcache_pool_stats_cpu *stats;
    > +
    > + stats = per_cpu_ptr(zpool->stats, cpu);
    > + do {
    > + start = u64_stats_fetch_begin(&stats->syncp);
    > + val += stats->count[idx];
    > + } while (u64_stats_fetch_retry(&stats->syncp, start));
    > + }
    > +
    > + BUG_ON(val < 0);
    > + return val;
    > +}

    Sorry this is wrong.

    Inside the fetch/retry block you should not do the addition to val, only
    a read of value to a temporary variable, since this might be done
    several times.

    You want something like :

    static u64 zcache_get_stat(struct zcache_pool *zpool,
    enum zcache_pool_stats_index idx)
    {
    int cpu;
    s64 temp, val = 0;

    for_each_possible_cpu(cpu) {
    unsigned int start;
    struct zcache_pool_stats_cpu *stats;

    stats = per_cpu_ptr(zpool->stats, cpu);
    do {
    start = u64_stats_fetch_begin(&stats->syncp);
    temp = stats->count[idx];
    } while (u64_stats_fetch_retry(&stats->syncp, start));
    val += temp;
    }

    ...
    }



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