Ceph BackoffThrottle分析

最新推荐文章于 2024-04-13 05:30:19 发布

for_tech

最新推荐文章于 2024-04-13 05:30:19 发布

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分类专栏： ceph原理 ceph源码剖析

本文链接：https://blog.csdn.net/for_tech/article/details/71174924

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本文深入分析了Ceph中的BackoffThrottle机制，特别是在filestore throttle中的应用。详细阐述了相关配置项、初始化过程以及delay值的计算方式，探讨了在不同压力情况下如何动态调整io速度，以减轻系统压力。通过实例比较了默认配置和优化配置下的dynamic throttle效果。

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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 
          ;

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