# Reduce\_sum cores, chains, threads

**URL:** <https://discourse.mc-stan.org/t/reduce-sum-cores-chains-threads/15114>\
**Category:** Interfaces\
**Tags:** cmdstanr\
**Created:** [May 13, 2020, 11:56pm UTC](https://discourse.mc-stan.org/t/reduce-sum-cores-chains-threads/15114 "2020-05-13T23:56:04Z")\
**Posts on this page:** 1\
**Showing post:** 9

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**Author:** ![shira](https://yyz2.discourse-cdn.com/flex030/user_avatar/discourse.mc-stan.org/shira/32/14161_2.png) [@shira](https://discourse.mc-stan.org/u/shira)\
**Post date:** [May 16, 2020, 3:04pm UTC](https://discourse.mc-stan.org/t/reduce-sum-cores-chains-threads/15114/9 "2020-05-16T15:04:27Z")

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I get no speed-up at all, following [Reduce Sum: A Minimal Example](https://mc-stan.org/users/documentation/case-studies/reduce_sum_tutorial.html). I tried my local machine and a cluster of cores, different values for chains, cores, threads, but I rarely get any speed-up at all, and never anywhere close to the 2.7 speed-up in the case study.

Attempting in regular CmdStan, to see if any speed-up is possible there, see [Cmdstanr reduce sum case study, but: unused argument (threads = TRUE)](https://discourse.mc-stan.org/t/cmdstanr-reduce-sum-case-study-but-unused-argument-threads-true/15105/5).

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