Analysis of LAS scheduling for job size distributions with high variance

Abstract

Recent studies of Internet traffic have shown that flow size distributions often exhibit a high variability property in the sense that most of the flows are short and more than half of the total load is constituted by a small percentage of the largest flows. In the light of this observation, it is interesting to revisit scheduling policies that are known to favor small jobs in order to quantify the benefit for small and the penalty for large jobs. Among all scheduling policies that do not require knowledge of job size, the least attained service (LAS) scheduling policy is known to favor small jobs the most. We investigate the M/G/1/LAS queue for both, load ? < 1 and ? = 1 . Our analysis shows that for job size distributions with a high variability property, LAS favors short jobs with a negligible penalty to the few largest jobs, and that LAS achieves a mean response time over all jobs that is close to the mean response time achieved by SRPT.Finally, we implement LAS in the ns-2 network simulator to study its performance benefits for TCP flows. When LAS is used to schedule packets over the bottleneck link, more than 99% of the shortest flows experience smaller mean response times under LAS than under FIFO and only the largest jobs observe a negligible increase in response time. The benefit of using LAS as compared to FIFO is most pronounced at high load.

Using multiple per egress burstifiers for enhanced TCP performance in OBS networks

“…A similar behavior is not observed in Fig. 13 since the burst losses are independent of the burst size for the flows destined to D 17 -D 20 .…”

“…We observe that for both destinations the average goodputs increase with the number of burstifiers. It is also observed that the average burst size increases linearly with the assembly timeout for flows destined to D 17 -D 20 . On the other hand, the average burst size first increases and then saturates for the flows destined to D 1 -D 4 .…”

“…We also observe from Figs. 12 and 13 that the flows destined for D 17 20 . In fact, the maximum goodput is achieved before the burst size saturates for the flows destined for D 1 -D 4 .…”

Stability of size-based scheduling disciplines in resource-sharing networks

“…While such information is typically available in web servers, it is usually nearly impossible to obtain in Internet routers. An alternative strategy which has therefore been advocated for scheduling data flows is the Least Attained Service first (LAS) discipline also known as ForegroundBackground Processor Sharing (FBPS) [22,27,29,30]. In case the service requirement distribution has a decreasing failure rate, it has been shown that LAS stochastically minimizes the number of jobs in the system among all strategies that use no knowledge of the remaining job sizes [31].…”

Decoupled speed scaling: Analysis and evaluation

“…Examples include Foreground-Background (FB) [26], Least Attained Service (LAS) [27], Resource Allocation Queueing Fairness Measure (RAQFM) [28], and the Fair Sojourn Protocol (FSP) [11]. FB and LAS approximate the effectiveness of SRPT, without the need to know job sizes in advance.…”