[Bug 1634161] [NEW] Default multipath policy is round-robin, shows considerably worse read throughput compared to using service-time

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---Problem Description---
Default multipath policy is round-robin, shows considerably worse read throughput compared to using service-time
Contact Information = Barbara Mundle, barbara.mundle at de.ibm.com 
---uname output---
4.4.0-21-generic
Machine Type = z systems: Type 2964, Model 701 NC9 
---Debugger---
A debugger is not configured
---Steps to Reproduce---
 Conducting throughput measurements with both policies shows the difference

Userspace tool common name: multipath-tools 
The userspace tool has the following bit modes: 64-bit 
Userspace rpm: multipath-tools_0.5.0+git1.656f8865-5ubuntu2.2_s390x.deb 
Userspace tool obtained from project website:  na 
 
*Additional Instructions for Barbara Mundle, barbara.mundle at de.ibm.com:
-Attach ltrace and strace of userspace application.

Throughput numbers with FIO for sequential read (in KBPS) with multipath
policies service.time/round-robin (varying with number of jobs from 1 -
64):

          service-time   round-robin

1        3193030         2917220 
2        5248430         5020375
4        8453570         6438140
8        9708690         6444175
16      9712100         6448080
32      9714035         6450905
64      9718355         6461650

** Affects: multipath-tools (Ubuntu)
     Importance: Undecided
     Assignee: Skipper Bug Screeners (skipper-screen-team)
         Status: New


** Tags: architecture-s39064 bugnameltc-147635 severity-high targetmilestone-inin---
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Default multipath policy is round-robin, shows considerably worse read throughput compared to using service-time
https://bugs.launchpad.net/bugs/1634161
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