Hello, Christoph.
> void __percpu_counter_add(struct percpu_counter *fbc, s64 amount, s32 batch)
> {
> - s64 count;
> + s64 count, new, overflow;
>
> - preempt_disable();
> - count = __this_cpu_read(*fbc->counters) + amount;
> - if (count >= batch || count <= -batch) {
> + do {
> + overflow = 0;
> + count = this_cpu_read(*fbc->counters);
> +
> + new = count + amount;
> + /* In case of overflow fold it into the global counter instead */
> + if (new >= batch || new <= -batch) {
> + overflow = new;
> + new = 0;
> + }
> +#ifdef CONFIG_PREEMPT
> + } while (this_cpu_cmpxchg(*fbc->counters, count, new) != count);
> +#else
> + } while (0);
> + this_cpu_write(*fbc->counters, new);
> +#endif
Eeeek, no. If you want to do the above, please put it in a separate
inline function with sufficient comment.
> + if (unlikely(overflow)) {
> spin_lock(&fbc->lock);
> - fbc->count += count;
> - __this_cpu_write(*fbc->counters, 0);
> + fbc->count += overflow;
> spin_unlock(&fbc->lock);
Why put this outside and use yet another branch?
Thanks.
--
tejun
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