Messages in this thread | | | Date | Tue, 1 Jan 2002 20:00:43 -0500 (EST) | From | Steinar Hauan <> | Subject | smp cputime issues |
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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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