If a multi-threaded program or code is run on a set of isolated cores using 'taskset' then all the program threads run on only one core.
Issue
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On a multi-CPU system, if more than one CPUs are isolated and if a multi-threaded program is run on it, then it has been observed that the program and all its child threads run only on a single CPU.
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It has been observed that the above statement is true if a multi-threaded program is run using non-RT scheduling policies like
SCHED_OTHER,SCHED_IDLE. -
But if the same application is run using RT scheduling policies like
SCHED_FIFO,SCHED_RR, then it has been observed that the multiple threads will be spread over isolated CPUs correctly. -
Here are brief examples of both the conditions :
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If say CPUs 5 and 7 are isolated, then using normal scheduling policies (On RHEL default scheduling policy is
SCHED_OTHER) will run the application 'fork' only on CPU 5.
# taskset -c 5-7 ./fork
- But if RT scheduling policies are used (here
SCHED_RRis selected), then the application will run on both the isolated CPUs.
# taskset -c 5-7 chrt -r 1 ./fork
Environment
- This is a generic observation, not limited to any specific RHEL (or Kernel) version.
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