[lttng-dev] [RFC] re-document rculfstack and even rename it

Mathieu Desnoyers mathieu.desnoyers at efficios.com
Thu Oct 11 14:22:55 EDT 2012

* Lai Jiangshan (laijs at cn.fujitsu.com) wrote:
> rculfstack is not really require RCU-only.
> 1) cds_lfs_push_rcu() don't need any lock, don't need RCU nor other locks.

Good point ! I even documented this peculiarness in the
comment at the top of _cds_lfs_push_rcu().

> 2) cds_lfs_pop_rcu() don't only one of the following synchronization(not only RCU):
> 	A) use rcu_read_lock() to protect cds_lfs_pop_rcu() and use synchronize_rcu()
>            or call_rcu() to free the popped node. (current comments said we need this
>            synchronization, and thus we named this struct with rcu prefix. But actually,
> 	   the followings are OK, and are more popular/friendly)
> 	B) use mutexs/locks to protect cds_lfs_pop_rcu(), we can free to free/modify the
> 	   popped node any time, we don't need any synchronization when free them.
> 	C) only ONE thread can call cds_lfs_pop_rcu(). (multi-providers-single customer)
> 	D) others, like read-write locks.
> I consider B) and C) are more popular. In linux kernel,
> kernel/task_work.c uses a hybird ways of B) and C).
> I suggest to rename it, Or document B) and C) at least.

Yes, agreed! Do you suggest we introduce a "lfstack", and slowly
deprecate rculfstack ?

We could then document the various ways to protect "pop", and also
implement a "splice" operation while we are there.

Thoughts ?



> Thanks,
> Lai
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Mathieu Desnoyers
Operating System Efficiency R&D Consultant
EfficiOS Inc.

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