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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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