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DateTue, 1 Jan 2002 20:00:43 -0500 (EST)
FromSteinar Hauan <>
Subjectsmp cputime issues
hello,

  we are encountering some weird timing behaviour on our linux cluster.

  specifically: when running 2 copies of selected programs on a
  dual-cpu system, the cputime reported for each process is up to 25%
  higher than when the processes are run on their own. however, if running
  two different jobs on the same machine, both complete with a cputime
  equal to when run individually. sample timing output attached.

  profiling confirms that everything slows down approximately to scale.
  the results reproduce on a range of different machines (see below).

additional specifications:
  - kernel version 2.4.16 (with apic enabled)
  - chipsets: apollo pro 133, apollo pro 266,
              intel i860, serverworks LE
  - all jobs requires less than 1/10 of physical memory
  - no significant disk i/o takes place
  - timing with dtime(), /usr/bin/time and shell built-in time
  - this behavior is NOT seen for all applications. the worst
    "offender" spends most of its time doing linear algebra.

  ideas or info-pointers appreciated. more specs available on request.

regards,
--
  Steinar Hauan, dept of ChemE  --  hauan@cmu.edu
  Carnegie Mellon University, Pittsburgh PA, USA
output from running a single image copy


[reported by dtime()]


CPU seconds spent in IPOPT and function evaluations =     131.9999982

[reported by /usr/bin/time -v ]


	Command being timed: "./ipopt robot_2000.nl"
	User time (seconds): 134.01
	System time (seconds): 0.36
	Percent of CPU this job got: 99%
	Elapsed (wall clock) time (h:mm:ss or m:ss): 2:14.42
	Average shared text size (kbytes): 0
	Average unshared data size (kbytes): 0
	Average stack size (kbytes): 0
	Average total size (kbytes): 0
	Maximum resident set size (kbytes): 0
	Average resident set size (kbytes): 0
	Major (requiring I/O) page faults: 293
	Minor (reclaiming a frame) page faults: 23352
	Voluntary context switches: 0
	Involuntary context switches: 0
	Swaps: 0
	File system inputs: 0
	File system outputs: 0
	Socket messages sent: 0
	Socket messages received: 0
	Signals delivered: 0
	Page size (bytes): 4096
	Exit status: 0
output from running two images simultaneously


[reported by dtime()]


CPU seconds spent in IPOPT and function evaluations =     157.7000024

[reported by /usr/bin/time -v ]

	Command being timed: "./ipopt robot_2000.nl"
	User time (seconds): 159.81
	System time (seconds): 0.50
	Percent of CPU this job got: 99%
	Elapsed (wall clock) time (h:mm:ss or m:ss): 2:40.41
	Average shared text size (kbytes): 0
	Average unshared data size (kbytes): 0
	Average stack size (kbytes): 0
	Average total size (kbytes): 0
	Maximum resident set size (kbytes): 0
	Average resident set size (kbytes): 0
	Major (requiring I/O) page faults: 293
	Minor (reclaiming a frame) page faults: 23352
	Voluntary context switches: 0
	Involuntary context switches: 0
	Swaps: 0
	File system inputs: 0
	File system outputs: 0
	Socket messages sent: 0
	Socket messages received: 0
	Signals delivered: 0
	Page size (bytes): 4096
	Exit status: 0
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