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Fewer Cores, More Hertz: Leveraging High-Frequency Cores in the OS Scheduler for Improved Application Performance

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Abstract

In modern server CPUs, individual cores can run at different frequencies, which allows for fine-grained control of the per-formance/energy tradeoff. Adjusting the frequency, however, incurs a high latency. We find that this can lead to a problem of frequency inversion, whereby the Linux scheduler places a newly active thread on an idle core that takes dozens to hundreds of milliseconds to reach a high frequency, just before another core already running at a high frequency becomes idle. In this paper, we first illustrate the significant performance overhead of repeated frequency inversion through a case study of scheduler behavior during the compilation of the Linux kernel on an 80-core Intel R Xeon-based machine. Following this, we propose two strategies to reduce the likelihood of frequency inversion in the Linux scheduler. When benchmarked over 60 diverse applications on the Intel R Xeon, the better performing strategy, S move , improves performance by more than 5% (at most 56% with no energy overhead) for 23 applications, and worsens performance by more than 5% (at most 8%) for only 3 applications. On a 4-core AMD Ryzen we obtain performance improvements up to 56%.
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Dates and versions

hal-02901169 , version 1 (16-07-2020)

Identifiers

  • HAL Id : hal-02901169 , version 1

Cite

Redha Gouicem, Damien Carver, Jean-Pierre Lozi, Julien Sopena, Baptiste Lepers, et al.. Fewer Cores, More Hertz: Leveraging High-Frequency Cores in the OS Scheduler for Improved Application Performance. 2020 USENIX Annual Technical Conference, USENIX, Jul 2020, Boston / Virtual, United States. ⟨hal-02901169⟩
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