On Mon, Jun 13, 2016 at 08:41:00AM -0000, Thomas Gleixner wrote:
> + * HZ 1000
> + * Level Offset Granularity Range
> + * 0 0 1 ms 0 ms - 63 ms
> + * 1 64 8 ms 64 ms - 511 ms
> + * 2 128 64 ms 512 ms - 4095 ms (512ms - ~4s)
> + * 3 192 512 ms 4096 ms - 32767 ms (~4s - ~32s)
> + * 4 256 4096 ms (~4s) 32768 ms - 262143 ms (~32s - ~4m)
> + * 5 320 32768 ms (~32s) 262144 ms - 2097151 ms (~4m - ~34m)
> +static int collect_expired_timers(struct timer_base *base,
> + struct hlist_head *heads)
> +{
> + unsigned long clock = base->clk;
> + struct hlist_head tmp, *vec;
> + int i, levels = 0;
> + unsigned int idx;
> +
> + /* Expire the regular buckets */
> + for (i = 0; i < LVL_DEPTH - 1; i++) {
> + idx = (clock & LVL_MASK) + i * LVL_SIZE;
> +
> + if (__test_and_clear_bit(idx, base->pending_map)) {
> + vec = base->vectors + idx;
> + hlist_move_list(vec, heads++);
> + levels++;
> + }
> + /* Is it time to look at the next level? */
> + if (clock & LVL_CLK_MASK)
> + return levels;
> + /* Shift clock for the next level granularity */
> + clock >>= LVL_CLK_SHIFT;
> + }
> +
> + /* Cascading, sigh... */
So given that userspace has no influence on timer period; can't we
simply fail to support timers longer than 30 minutes?
In anything really arming timers _that_ long?
> + idx = (clock & LVL_MASK) + i * LVL_SIZE;
> +
> + if (__test_and_clear_bit(idx, base->pending_map)) {
> + vec = base->vectors + idx;
> + hlist_move_list(vec, &tmp);
> + /* Make sure we queue them in the future */
> + base->clk++;
> + while (!hlist_empty(&tmp)) {
> + struct timer_list *timer;
> +
> + timer = hlist_entry(tmp.first, struct timer_list,
> entry);
> + trace_timer_cascade(timer);
> + __hlist_del(&timer->entry);
> + __internal_add_timer(base, timer);
> + }
> + base->clk--;
> + }
> + return levels;
> +}
