Ceph BackoffThrottle分析

本文讨论下Ceph在Jewel中引入的 dynamic throttle：BackoffThrottle；分析后优化Ceph filestore，journal相关的throttle配置；

参考文章：

http://blog.wjin.org/posts/ceph-dynamic-throttle.html

https://fossies.org/linux/ceph/src/doc/dynamic-throttle.txt

BackoffThrottle

Jewel引入了dynamic的throttle，就是代码中BackoffThrottle，现在filestore和Journal都是使用它来做throttle的；

class  FileStore {      BackoffThrottle throttle_ops, throttle_bytes; }   class  JournalThrottle {      BackoffThrottle throttle; … }

BackoffThrottle定义和相关参数如下：

/**   * BackoffThrottle   *   * Creates a throttle which gradually induces delays when get() is called   * based on params low_threshhold, high_threshhold, expected_throughput,   * high_multiple, and max_multiple.   *   * In [0, low_threshhold), we want no delay.   *   * In [low_threshhold, high_threshhold), delays should be injected based   * on a line from 0 at low_threshhold to   * high_multiple * (1/expected_throughput) at high_threshhold.   *   * In [high_threshhold, 1), we want delays injected based on a line from   * (high_multiple * (1/expected_throughput)) at high_threshhold to   * (high_multiple * (1/expected_throughput)) +   * (max_multiple * (1/expected_throughput)) at 1.   *   * Let the current throttle ratio (current/max) be r, low_threshhold be l,   * high_threshhold be h, high_delay (high_multiple / expected_throughput) be e,   * and max_delay (max_muliple / expected_throughput) be m.   *   * delay = 0, r \in [0, l)   * delay = (r - l) * (e / (h - l)), r \in [l, h)   * delay = h + (r - h)((m - e)/(1 - h))   */ class  BackoffThrottle { …      /// see above, values are in [0, 1].      double  low_threshhold =  0 ;      double  high_threshhold =  1 ;