Messages in this thread | | | Date | Mon, 1 Sep 2008 18:05:44 -0700 | From | "Paul E. McKenney" <> | Subject | Re: [PATCH, RFC, tip/core/rcu] v3 scalable classic RCU implementation |
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On Mon, Sep 01, 2008 at 11:38:29AM +0200, Andi Kleen wrote: > "Paul E. McKenney" <paulmck@linux.vnet.ibm.com> writes: > > > > -#if defined(CONFIG_PREEMPT_RCU) && defined(CONFIG_NO_HZ) > > +#if defined(CONFIG_NO_HZ) > > extern void rcu_irq_enter(void); > > extern void rcu_irq_exit(void); > > #else > > # define rcu_irq_enter() do { } while (0) > > # define rcu_irq_exit() do { } while (0) > > -#endif /* CONFIG_PREEMPT_RCU */ > > +#endif /* #if defined(CONFIG_NO_HZ) */ > > It would be better if you hung rcu_irq_enter in the irq_enter() if > statement that checks if the task was idle or not. This way it would > be zero overhead for interruptions of non busy CPUs, keeping > it out of many fast paths. > > Haven't read everything, sorry.
So that I lose the #else above, and so that irq_enter() and irq_exit() look something like the following (with additional adjustments to suit)? Makes a lot of sense to me...
And it has the very nice side effect of allowing me to have a separate rcu_irq_enter() and rcu_nmi_enter(), trivializing the RCU-dynticks interface!!! Very cool, thank you very much!!!
Thanx, Paul
void irq_enter(void) { #ifdef CONFIG_NO_HZ int cpu = smp_processor_id(); if (idle_cpu(cpu) && !in_interrupt()) tick_nohz_stop_idle(cpu); #endif __irq_enter(); #ifdef CONFIG_NO_HZ if (idle_cpu(cpu)) { rcu_irq_enter(); tick_nohz_update_jiffies(); } #endif }
void irq_exit(void) { account_system_vtime(current); trace_hardirq_exit(); sub_preempt_count(IRQ_EXIT_OFFSET); if (!in_interrupt() && local_softirq_pending()) invoke_softirq();
#ifdef CONFIG_NO_HZ /* Make sure that timer wheel updates are propagated */ if (idle_cpu(smp_processor_id())) { if (!in_interrupt() && !need_resched()) tick_nohz_stop_sched_tick(0); rcu_irq_exit(); } #endif preempt_enable_no_resched(); }
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