Messages in this thread Patch in this message | | | Date | Tue, 17 Jan 2006 18:49:48 -0800 | From | "Paul E. McKenney" <> | Subject | Re: [Lse-tech] Re: [ckrm-tech] Re: [PATCH 00/01] Move Exit Connectors |
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On Wed, Jan 18, 2006 at 10:57:47AM +1100, Keith Owens wrote: > "Paul E. McKenney" (on Tue, 17 Jan 2006 09:26:17 -0800) wrote: [ . . .] > >One other thing -- given that you are requiring that the read side > >have preemption disabled, another update-side option would be to > >use synchronize_sched() to wait for all preemption-disabled code > >segments to complete. This would allow you to remove the per-CPU > >reference counters from the read side, but would require that the > >update side either (1) be able to block or (2) be able to defer > >the cleanup to process context. > > Originally I looked at that code but the comment scared me off. > synchronize_sched() maps to synchronize_rcu() and the comment says that > this only protects against rcu_read_lock(), not against preempt_disable().
Good point -- in mainline kernels (but not in some realtime variants), the two guarantees happen to be one and the same. But the comment certainly does not make this clear.
> /** > * synchronize_sched - block until all CPUs have exited any non-preemptive > * kernel code sequences. > * > * This means that all preempt_disable code sequences, including NMI and > * hardware-interrupt handlers, in progress on entry will have completed > * before this primitive returns. However, this does not guarantee that > * softirq handlers will have completed, since in some kernels > * > * This primitive provides the guarantees made by the (deprecated) > * synchronize_kernel() API. In contrast, synchronize_rcu() only > * guarantees that rcu_read_lock() sections will have completed. > */ > #define synchronize_sched() synchronize_rcu()
Does the following change help?
Thanx, Paul
diff -urpNa -X dontdiff linux-2.6.15/include/linux/rcupdate.h linux-2.6.15-RCUcomment/include/linux/rcupdate.h --- linux-2.6.15/include/linux/rcupdate.h 2006-01-02 19:21:10.000000000 -0800 +++ linux-2.6.15-RCUcomment/include/linux/rcupdate.h 2006-01-17 18:48:33.000000000 -0800 @@ -265,11 +265,14 @@ static inline int rcu_pending(int cpu) * This means that all preempt_disable code sequences, including NMI and * hardware-interrupt handlers, in progress on entry will have completed * before this primitive returns. However, this does not guarantee that - * softirq handlers will have completed, since in some kernels + * softirq handlers will have completed, since in some kernels, these + * handlers can run in process context, and can block. * * This primitive provides the guarantees made by the (deprecated) * synchronize_kernel() API. In contrast, synchronize_rcu() only * guarantees that rcu_read_lock() sections will have completed. + * In "classic RCU", these two guarantees happen to be one and + * the same, but can differ in realtime RCU implementations. */ #define synchronize_sched() synchronize_rcu() - 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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