if (rcu_pending(cpu))
rcu_check_callbacks(cpu, user_tick);
．．．．．．
．．．．．．
}
在每一次时钟中断,都会检查是否有需要更新的RCU需要处理,如果有,就会为其调用rcu_check_callbacks().
Rcu_pending()的代码如下:
int rcu_pending(int cpu)
{
return __rcu_pending(&rcu_ctrlblk, &per_cpu(rcu_data, cpu)) ||
__rcu_pending(&rcu_bh_ctrlblk, &per_cpu(rcu_bh_data, cpu));
}
同上面一样,忽略bh的部份.
static int __rcu_pending(struct rcu_ctrlblk *rcp, struct rcu_data *rdp)
{
/* This cpu has pending rcu entries and the grace period
* for them has completed.
*/
if (rdp->curlist && !rcu_batch_before(rcp->completed, rdp->batch))
return 1;
/* This cpu has no pending entries, but there are new entries */
if (!rdp->curlist && rdp->nxtlist)
return 1;
/* This cpu has finished callbacks to invoke */
if (rdp->donelist)
return 1;
/* The rcu core waits for a quiescent state from the cpu */
if (rdp->quiescbatch != rcp->cur || rdp->qs_pending)
return 1;
/* nothing to do */
return 0;
}
上面有四种情况会返回1,分别对应:
1:该CPU上有等待处理的回调函数,且已经经过了一个batch(grace period).rdp->datch表示rdp在等待的batch序号
2:上一个等待已经处理完了,又有了新注册的回调函数.
3:等待已经完成,但尚末调用该次等待的回调函数.
4:在等待quiescent state.
关于rcp和rdp结构中成员的含义,我们等用到的时候再来分析.
/* Grace period already completed for this cpu?
* qs_pending is checked instead of the actual bitmap to avoid
* cacheline trashing.
*/
if (!rdp->qs_pending)
return;
/*
* Was there a quiescent state since the beginning of the grace
* period? If no, then exit and wait for the next call.
*/
if (!rdp->passed_quiesc)
return;
rdp->qs_pending = 0;
spin_lock(&rcp->lock);
/*
* rdp->quiescbatch/rcp->cur and the cpu bitmap can come out of sync
* during cpu startup. Ignore the quiescent state.
*/
if (likely(rdp->quiescbatch == rcp->cur))
cpu_quiet(rdp->cpu, rcp);
list = rdp->donelist;
while (list) {
next = list->next;
prefetch(next);
list->func(list);
list = next;
if (++count >= rdp->blimit)
break;
}
rdp->donelist = list;