2008-08-04 15:47:50

by TAKADA Yoshihito

Subject: How does RCU work?

Hi.
I cannot understand mechanism. Somebody tell me it please.

In x86 kernel, CONFIG_PREEMPT_RCU=n (CONFIG_CLASSIC_RCU=y). rcu_read_lock() makes
just preempt_disable().
call_cru()/synchronize_rcu() running as a soft-IRQ.
It's current CPU does not refer to protected data that when call_rcu() run.
Because soft-IRQ handler ran, it means current CPU is preempive. That is the CPU
called rcu_read_unlock().

Well, current CPU is unlocked, but How does kernel know it other CPUs unlocked?

call_ruc() calls force_quiescent_state() to reschedule other CPUs.
force_quiescent_state() calls smp_send_reschedule() to sends request to reshecule.
It's just require to reschedule via inter Processor Interrupt. But call_rcu() does
not wait for target CPUs handle IPI. Or, Do CPUs have it handled IPI request when
return from smp_send_reschedule()?

2008-08-04 18:18:43

by Bert Wesarg

Subject: Re: How does RCU work?

On Mon, Aug 4, 2008 at 17:09, TAKADA Yoshihito <[email protected]> wrote:
> Hi.
> I cannot understand mechanism. Somebody tell me it please.
There are plenty of resources on the net. Try:

http://www.rdrop.com/users/paulmck/RCU/
http://en.wikipedia.org/wiki/RCU

Regards
Bert