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This change has been made by an automated script, maintained by the
Ubuntu Kernel Team.
** Changed in: linux (Ubuntu)
Status: New => Incomplete
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https://bugs.launchpad.net/bugs/1315619
Title:
Job with 4 threads not assigned 4 distinct cores
Status in “linux” package in Ubuntu:
Incomplete
Bug description:
On 12.04, I have reliably found that a job which starts 4 long-running
threads on an otherwise-idle machine (there are some other threads
which have been running for some time, but they have been kill
-STOPped) gets the threads allocated to 4 distinct cores on my
Haswell.
On 14.04, I found that the threads were allocated to cores 0, 1, 5, 6
- that is, two were running on the two hyper-threads 1 and 5 of the
same core, and performance was 30% less than expected. I can get
around this with explicit taskset commands, but for my use case it's a
serious regression from 12.04.
I am not willing to disable hyperthreading, because it gives a large
performance boost on other things I do on the same machine.
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