[lttng-dev] [RFC PATCH liburcu 0/2] Remove RCU requirements on hash table destroy

[Mathieu Desnoyers]

----- On Jun 5, 2017, at 6:56 PM, Paul E. McKenney paulmck at linux.vnet.ibm.com wrote:

> On Tue, May 30, 2017 at 05:10:18PM -0400, Mathieu Desnoyers wrote:
>> The RCU lock-free hash table currently requires that the destroy
>> function should not be called from within RCU read-side critical
>> sections. This is caused by the lazy resize, which uses the call_rcu
>> worker thread, even though all it really needs is a workqueue/worker
>> thread scheme.
>> 
>> Implement an internal workqueue API in liburcu, and use it instead of
>> call_rcu in rculfhash to overcome this limitation.
> 
> Took a quick look, and it appears plausible.
> 
> Some opportunity to share CPU-affinity code between this and the
> call_rcu() code, FWIW.

Given that I plan to reimplement the call_rcu code using this new
internal workqueue API, I don't think it is useful to try to lift
out the duplicated code between call_rcu and workqueue. When call_rcu
is reimplemented, the duplicated cpu affinity code will vanish.

>  Two of the system-call stubs look to be identical
> other than the system call (EINTR checks and soforth), but I am not sure
> that it is worth combining them.

Are you talking about the futex wait/wakeup ? If so, would the
attached patch that combine those work for you ? I noticed that
even the error handling is identical.

Thanks,

Mathieu


-- 
Mathieu Desnoyers
EfficiOS Inc.
http://www.efficios.com
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