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    SubjectRe: [patch] cpufreq: mark cpufreq_tsc() as core_initcall_sync
    Ok, synchronize_xxx() passed 1 hour rcutorture test on dual P-III.

    It behaves the same as srcu but optimized for writers. The fast path
    for synchronize_xxx() is mutex_lock() + atomic_read() + mutex_unlock().
    The slow path is __wait_event(), no polling. However, the reader does
    atomic inc/dec on lock/unlock, and the counters are not per-cpu.

    Jens, is it ok for you? Alan, Paul, what is your opinion?

    Oleg.

    --- 19-rc6/kernel/__rcutorture.c 2006-11-17 19:42:31.000000000 +0300
    +++ 19-rc6/kernel/rcutorture.c 2006-11-24 21:00:00.000000000 +0300
    @@ -464,6 +464,120 @@ static struct rcu_torture_ops srcu_ops =
    .name = "srcu"
    };

    +//-----------------------------------------------------------------------------
    +struct xxx_struct {
    + int completed;
    + atomic_t ctr[2];
    + struct mutex mutex;
    + wait_queue_head_t wq;
    +};
    +
    +void init_xxx_struct(struct xxx_struct *sp)
    +{
    + sp->completed = 0;
    + atomic_set(sp->ctr + 0, 1);
    + atomic_set(sp->ctr + 1, 0);
    + mutex_init(&sp->mutex);
    + init_waitqueue_head(&sp->wq);
    +}
    +
    +int xxx_read_lock(struct xxx_struct *sp)
    +{
    + for (;;) {
    + int idx = sp->completed & 0x1;
    + if (likely(atomic_inc_not_zero(sp->ctr + idx)))
    + return idx;
    + }
    +}
    +
    +void xxx_read_unlock(struct xxx_struct *sp, int idx)
    +{
    + if (unlikely(atomic_dec_and_test(sp->ctr + idx)))
    + wake_up(&sp->wq);
    +}
    +
    +void synchronize_xxx(struct xxx_struct *sp)
    +{
    + int idx;
    +
    + mutex_lock(&sp->mutex);
    +
    + idx = sp->completed & 0x1;
    + if (!atomic_add_unless(sp->ctr + idx, -1, 1))
    + goto out;
    +
    + atomic_inc(sp->ctr + (idx ^ 0x1));
    + sp->completed++;
    +
    + __wait_event(sp->wq, !atomic_read(sp->ctr + idx));
    +out:
    + mutex_unlock(&sp->mutex);
    +}
    +
    +//-----------------------------------------------------------------------------
    +static struct xxx_struct xxx_ctl;
    +
    +static void xxx_torture_init(void)
    +{
    + init_xxx_struct(&xxx_ctl);
    + rcu_sync_torture_init();
    +}
    +
    +static void xxx_torture_cleanup(void)
    +{
    + synchronize_xxx(&xxx_ctl);
    +}
    +
    +static int xxx_torture_read_lock(void)
    +{
    + return xxx_read_lock(&xxx_ctl);
    +}
    +
    +static void xxx_torture_read_unlock(int idx)
    +{
    + xxx_read_unlock(&xxx_ctl, idx);
    +}
    +
    +static int xxx_torture_completed(void)
    +{
    + return xxx_ctl.completed;
    +}
    +
    +static void xxx_torture_synchronize(void)
    +{
    + synchronize_xxx(&xxx_ctl);
    +}
    +
    +static int xxx_torture_stats(char *page)
    +{
    + int cnt = 0;
    + int idx = xxx_ctl.completed & 0x1;
    +
    + cnt += sprintf(&page[cnt], "%s%s per-CPU(idx=%d):",
    + torture_type, TORTURE_FLAG, idx);
    +
    + cnt += sprintf(&page[cnt], " (%d,%d)",
    + atomic_read(xxx_ctl.ctr + 0),
    + atomic_read(xxx_ctl.ctr + 1));
    +
    + cnt += sprintf(&page[cnt], "\n");
    + return cnt;
    +}
    +
    +static struct rcu_torture_ops xxx_ops = {
    + .init = xxx_torture_init,
    + .cleanup = xxx_torture_cleanup,
    + .readlock = xxx_torture_read_lock,
    + .readdelay = srcu_read_delay,
    + .readunlock = xxx_torture_read_unlock,
    + .completed = xxx_torture_completed,
    + .deferredfree = rcu_sync_torture_deferred_free,
    + .sync = xxx_torture_synchronize,
    + .stats = xxx_torture_stats,
    + .name = "xxx"
    +};
    +//-----------------------------------------------------------------------------
    +
    /*
    * Definitions for sched torture testing.
    */
    @@ -503,8 +617,8 @@ static struct rcu_torture_ops sched_ops
    };

    static struct rcu_torture_ops *torture_ops[] =
    - { &rcu_ops, &rcu_sync_ops, &rcu_bh_ops, &rcu_bh_sync_ops, &srcu_ops,
    - &sched_ops, NULL };
    + { &rcu_ops, &rcu_sync_ops, &rcu_bh_ops, &rcu_bh_sync_ops,
    + &srcu_ops, &xxx_ops, &sched_ops, NULL };

    /*
    * RCU torture writer kthread. Repeatedly substitutes a new structure
    -
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