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Francesco Nigro commented on DISPATCH-1372: ------------------------------------------- Below the flamegraph of a 1 pair + router cache-misses events. On master with the original allocator: !image-2019-06-21-11-08-17-015.png! On masterbut with a linked stack allocator: !image-2019-06-21-11-09-02-228.png! In violet there are the calls to qd_alloc. To explain the improvement, the relative samples for qd_buffer in _qd_buffer_list_clone are: master linked list: 277 samples master linked stack: 54 samples The overall cache misses on the router_core_thread instead are: master linked list: 1817 samples master linked stack: 1488 samples The improvement has yet to be verified under load with more clients, but seems promising. > alloc_pool intrusive linked list can be replaced by a linked stack > ------------------------------------------------------------------ > > Key: DISPATCH-1372 > URL: https://issues.apache.org/jira/browse/DISPATCH-1372 > Project: Qpid Dispatch > Issue Type: Improvement > Components: Routing Engine > Affects Versions: 1.8.0 > Reporter: Francesco Nigro > Priority: Major > Attachments: DOOM-3-BFG-Technical-Note.pdf, > image-2019-06-21-11-08-17-015.png, image-2019-06-21-11-09-02-228.png, > linked_list_misses.svg, stack_list_misses.svg > > > alloc_pool is currently using a intrusive linked list approach to reduce the > need of external data structures to hold data, saving expensive pointer > chasing, but on modern architectures the data dependency between a current > node and next/prev prevent the CPU prefetcher to stream nodes speculatively. > There are different approaches that could benefit of prefetcing, but need to > decouple the data stored from its container eg a linked stack. > A linked stack is composed by doubly-linked chunks (allocated lazily) that > make possible for the CPU to prefetch next/prev pointers given that those are > already contained in the current chunk (if any). > Although it seems counter-intuitive (given that introduce 1 more hop to reach > the data), such data-structure is much more cache-friendly on modern > architectures: I will attach some cache misses analysis to show it. > -- This message was sent by Atlassian JIRA (v7.6.3#76005) --------------------------------------------------------------------- To unsubscribe, e-mail: dev-unsubscr...@qpid.apache.org For additional commands, e-mail: dev-h...@qpid.apache.org