[lttng-dev] RCU consistency guarantees

[Mathieu Desnoyers]

----- On Dec 6, 2019, at 3:51 PM, Yuxin Ren <ryx at gwmail.gwu.edu> wrote: 

> On Fri, Dec 6, 2019 at 5:49 AM Mathieu Desnoyers < [
> mailto:mathieu.desnoyers at efficios.com | mathieu.desnoyers at efficios.com ] >
> wrote:

>> ----- On Dec 5, 2019, at 8:17 PM, Yuxin Ren < [ mailto:ryx at gwmail.gwu.edu |
>> ryx at gwmail.gwu.edu ] > wrote:

>>> Hi,
>>> I am a student, and learning RCU now, but still know very little about it.
>>> Are there any documents/papers/materials which (in)formally define and explain
>>> RCU consistency guarantees?

>> You may want to have a look at

>> User-Level Implementations of Read-Copy Update
>> Article in IEEE Transactions on Parallel and Distributed Systems 23(2):375 - 382
>> · March 2012

> Thanks for your info.
> However, I do not think URCU talks about any consistency model formally.

> From previous communication with Paul, he said RCU is not designed for
> linearizability, and it is totally acceptable that RCU is not linearizable.
> However, I am curious how to accurately/formally Characterize RCU consistency
> model/guarantees

Adding Paul E. McKenney in CC. 

I am referring to the section "Overview of RCU semantics" in the paper. Not sure it has the level of 
formality you are looking for though. Paul, do you have pointers to additional material ? 

Thanks, 

Mathieu 

>> as a starting point.

>> Thanks,

>> Mathieu

>>> I know there are some consistency models in the database area (such as PRAM,
>>> Read Uncommitted, etc) from [ https://jepsen.io/consistency |
>>> https://jepsen.io/consistency ] and [1].
>>> How does RCU related to those consistency models?

>>> I also found some comments online (One key distinction is that both MVCC and RLU
>>> provide much stronger consistency guarantees to readers than does RCU ...) ( [
>>> https://lwn.net/Articles/777036/ | https://lwn.net/Articles/777036/ ] ).
>>> I do not understand how we reason/dresibe/compare the consistency guarantees. (
>>> I even do not know what consistency guarantees provided by RCU formally)
>>> Could someone explain this to me?

>>> [1] Bailis, P., Davidson, A., Fekete, A., Ghodsi, A., Hellerstein, J. M., &
>>> Stoica, I. (2013). Highly available transactions: Virtues and limitations.
>>> Proceedings of the VLDB Endowment, 7(3), 181-192.

>>> Thanks
>>> Yuxin

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>> --
>> Mathieu Desnoyers
>> EfficiOS Inc.
>> [ http://www.efficios.com/ | http://www.efficios.com ]

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