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Why Non-Blocking Operations Should Be Selfish

Abstract : Non-blocking data structures are often analysed by giving an upper amortised running time bound in terms of the size of the data structure and a measure of contention. The two most commonly used measures are the point contention cP , the maximum number of processes active at any one time during an operation, and the interval contention cI , the number of operations overlapping with a given operation. In this paper, we show that when summed across every operation in an exe- cution, the interval contention cI is within a factor of 2 of the point contention cP . Our proof relies on properties of interval graphs where at least one simplicial vertex exists, and uses it to construct a lower bound on the overall point contention. We show that this bound is tight. This result contradicts the folklore belief that point contention leads to a tighter bound on complexity in an amortised context, and provides some theoretical grounds for recent observations that using less helping in non-blocking data structures can lead to better performance. We also propose a linked list algorithm based on Fomitchev and Ruppert’s algorithm but with selfish operations: read-only operations that do not help others but rather execute wait-free. The higher performance of our approach compared to the original list confirms that reducing helping can increase performance, with the same asymptotic amortised complexity.
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https://hal.archives-ouvertes.fr/hal-01206442
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Submitted on : Tuesday, September 29, 2015 - 9:56:44 AM
Last modification on : Wednesday, February 19, 2020 - 1:10:04 PM
Long-term archiving on: : Wednesday, December 30, 2015 - 10:22:04 AM

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Joel Gibson, Vincent Gramoli. Why Non-Blocking Operations Should Be Selfish. DISC 2015, Toshimitsu Masuzawa; Koichi Wada, Oct 2015, Tokyo, Japan. ⟨10.1007/978-3-662-48653-5_14⟩. ⟨hal-01206442⟩

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