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Posted to dev@qpid.apache.org by "ASF GitHub Bot (JIRA)" <ji...@apache.org> on 2019/06/25 13:43:00 UTC
[jira] [Commented] (DISPATCH-1342) Replaced mutex with spin lock on
qd_message content
[ https://issues.apache.org/jira/browse/DISPATCH-1342?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16872359#comment-16872359 ]
ASF GitHub Bot commented on DISPATCH-1342:
------------------------------------------
franz1981 commented on issue #508: DISPATCH-1342 Replaced mutex with spin lock on qd_message content
URL: https://github.com/apache/qpid-dispatch/pull/508#issuecomment-505450597
@astitcher Totally agree, that's why I haven't replaced the mutexes for any possible use case; there are some requirements that need to be satisfied in order to make this change effective (or feasable).
We need to:
- be sure no reentrancy is happening on the mutual exclusion zone (and it seems the case, looking the code)
- be sure that the mutual exclusion zone is not held for too much time (to be defined) and none is blocked on it
If both these requirements are met, only proper benchmarking and tests can tell us if the spin lock is the right answer here. I would stick to something that won't require OS arbitrations on the hot path anyway: OS is like burocrazy and I won't bother it when user-space matters can already solve things with a more predictable latencies
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> Replaced mutex with spin lock on qd_message content
> ---------------------------------------------------
>
> Key: DISPATCH-1342
> URL: https://issues.apache.org/jira/browse/DISPATCH-1342
> Project: Qpid Dispatch
> Issue Type: Improvement
> Components: Routing Engine
> Affects Versions: 1.7.0
> Reporter: Francesco Nigro
> Priority: Minor
>
> Given that qd_message creation and qd_message_free involves sys_mutex allocation/free and they are OS resources too, using spin locks will reduce the CPU/memory usage while performing such frequent operations.
> In addition it would make the router more reactive and resilient to OS thread scheduling while message->content is being concurrently accessed too, given that such accesses are meant to not last long and there is no need to involve OS arbitration to park/awake threads,
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