Type of Document Thesis Author Stanovich, Mark J Author's Email Address email@example.com URN etd-04142008-232323 Title Throttling On-Disk Schedulers to Meet Soft-Real-Time Requirements Degree Master of Science Department Computer Science, Department of Advisory Committee
Advisor Name Title Theodore P. Baker Committee Chair An-I Andy Wang Committee Member Piyush Kumar Committee Member Keywords
- disk scheduling
Date of Defense 2008-04-03 Availability unrestricted AbstractMany contemporary disk drives have built-in queues and schedulers. These features can
improve I/O performance, by offloading work from the systemís main processor, avoiding
disk idle time, and taking advantage of vendor-specific disk characteristics. At the same
time, they pose challenges for scheduling requests that have real-time requirements, since the
operating system has less visibility and control over service times. While it may be possible
for an operating system to obtain more predictable real-time performance by bypassing the
on-disk queue and scheduler, the diversity and continuing evolution of disk drives make it
difficult to extract the necessary detailed timing characteristics of a specific disk, and to
generalize that approach to all hard drives.
This paper demonstrates three techniques we developed in the Linux operating system to
bound real-time request response times for disks with internal queues and schedulers. The
first technique is to use the diskís built-in starvation prevention scheme. The second is to
prevent requests from being sent to the disk when real-time requests are waiting to be served.
The third is to limit the length of the on-disk queue in addition to the second technique.
Our results show the ability to guarantee a wide range of desired response times while still
allowing the disk to perform scheduling optimizations. These techniques can be generalized
to disks from different vendors, as well as other operating systems.
Filename Size Approximate Download Time (Hours:Minutes:Seconds)
28.8 Modem 56K Modem ISDN (64 Kb) ISDN (128 Kb) Higher-speed Access StanovichJThesis.pdf 450.09 Kb 00:02:05 00:01:04 00:00:56 00:00:28 00:00:02