Re: [patch 16/23] dynticks: core

On Sat, Sep 30, 2006 at 01:44:56AM -0700, Andrew Morton wrote:
On Fri, 29 Sep 2006 23:58:35 -0000
Thomas Gleixner <tglx@xxxxxxxxxxxxx> wrote:

From: Ingo Molnar <mingo@xxxxxxx>

dynticks core code.

Add idling-stats to the cpu base (to be used to optimize power
management decisions), add the scheduler tick and its stop/restart
functions, and the jiffies-update function to be called when an irq
context hits the idle context.


I worry that we're making this feature optional.
+ /*
+ * RCU normally depends on the timer IRQ kicking completion
+ * in every tick. We have to do this here now:
+ */
+ if (rcu_pending(cpu)) {
+ /*
+ * We are in quiescent state, so advance callbacks:
+ */
+ rcu_advance_callbacks(cpu, 1);
+ local_irq_enable(); <----------------- Here
+ local_bh_disable();
+ rcu_process_callbacks(0);
+ local_bh_enable();
+ }
+
+ local_irq_restore(flags);
+
+ return need_resched();
+}

Are the RCU guys OK with this?

What prevents more RCU callbacks getting queued up by an
irq after irqs are enabled (marked Here) ? This seems racy.
The s390 implementation is correct - there we back out
if RCU is pending. Also, one call
to rcu_process_callbacks() doesn't guarantee that all
the RCUs are processed. They can be rate limited.

Thanks
Dipankar
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