Messages in this thread | | | From | Herbert Xu <> | Subject | Re: [patch] Real-Time Preemption, -RT-2.6.12-rc1-V0.7.41-07 | Date | Wed, 23 Mar 2005 20:38:11 +1100 |
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Ingo Molnar <mingo@elte.hu> wrote: > > * Paul E. McKenney <paulmck@us.ibm.com> wrote: > >> +#ifdef CONFIG_PREEMPT_RCU >> + >> +void rcu_read_lock(void) >> +{ >> + if (current->rcu_read_lock_nesting++ == 0) { >> + current->rcu_data = &get_cpu_var(rcu_data); >> + atomic_inc(¤t->rcu_data->active_readers); >> + put_cpu_var(rcu_data); >> >> Need an smp_mb() here for non-x86 CPUs. Otherwise, the CPU can >> re-order parts of the critical section to precede the rcu_read_lock(). >> Could precede the put_cpu_var(), but why increase latency? > > ok. It's enough to put a barrier into the else branch here, because the > atomic op in the main brain is a barrier by itself.
Since the else branch is only taken when rcu_read_lock_nesting > 0, do we need the barrier at all?
Cheers, -- Visit Openswan at http://www.openswan.org/ Email: Herbert Xu ~{PmV>HI~} <herbert@gondor.apana.org.au> Home Page: http://gondor.apana.org.au/~herbert/ PGP Key: http://gondor.apana.org.au/~herbert/pubkey.txt - To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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