阅读周记(第一期)


Save Some Bandwidth By Turning Off TCP Timestamps

想法: tcp timestamp选项会引入额外的12字节的包头开销,因此关闭tcp timestamp选项理论上能够少量的提高有效数据的吞吐率
评测: 使用qperf benchmark评测关闭tcp timestamp后,能提升大约1%的吞吐率
      对于10GE NIC,关闭timestamp能将下载速度从9370Mbits/s提升至9460Mbits/s
点评: 关闭timestamp正常情况下确实能提高有效数据的吞吐率,但在某些情况下可能就不那么理想了。
      比如timestamp提出的初衷之一就是解决RTT测量不准,导致spurious retransmission的情况。如果关闭timestamp导致了更多的RTO,则肯定是划不来的。  
      正如文中建议的:
        Results show that it is reasonable to turn off timestamps on 10GE interfaces, 
        but keep in mind that it should be performed only in low latency networks.
      使用10GE网卡是为了1%的提升效果更明显,强调低延迟是因为RTO有系统最小值200ms限制。低延迟下更难出现spurious retransmission

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What benefit is conferred by TCP timestamp?

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