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Posted to dev@qpid.apache.org by "Francesco Nigro (JIRA)" <ji...@apache.org> on 2019/06/03 09:06:00 UTC
[jira] [Commented] (DISPATCH-1352) qd_buffer_list_clone cost is
dominated by cache misses
[ https://issues.apache.org/jira/browse/DISPATCH-1352?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16854399#comment-16854399 ]
Francesco Nigro commented on DISPATCH-1352:
-------------------------------------------
!screenshot-1.png!
This flame graph show that qd_alloc and qd_buffer_size respectively on the dst and src qd_buffer_list_t's qd_buffer_t elements are a dominant factors that steal precious cpu time.
The overall picture of this is (in violet):
!screenshot-2.png!
It shows that a non maxed out core thread spent a significant amount of cpu resources to perform such copy: further analysis has shown that this time is not actually spent doing somthing, but waiting cache misses.
> qd_buffer_list_clone cost is dominated by cache misses
> ------------------------------------------------------
>
> Key: DISPATCH-1352
> URL: https://issues.apache.org/jira/browse/DISPATCH-1352
> Project: Qpid Dispatch
> Issue Type: Improvement
> Components: Routing Engine
> Affects Versions: 1.7.0
> Reporter: Francesco Nigro
> Priority: Major
> Attachments: screenshot-1.png, screenshot-2.png
>
>
> qd_buffer_list_clone on qd_message_copy for qd_message_pvt_t.ma_to_override/ma_trace/ma_ingress is dominated by cache misses costs:
> * to "allocate" new qd_buffer_t
> * to reference any qd_buffer_t from the source qd_buffer_list_t
> Such cost is the main reason why the core thread is having a very low IPC (< 1 istr/cycle) and given the single threaded nature of the router while dealing with it, by solving it will bring a huge performance improvement to make the router able to scale better.
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