Messages in this thread | | | Subject | Re: CFS scheduler unfairly prefers pinned tasks | From | Wanpeng Li <> | Date | Sat, 10 Oct 2015 11:59:41 +0800 |
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Hi Paul, On 10/8/15 4:19 PM, Mike Galbraith wrote: > On Tue, 2015-10-06 at 04:45 +0200, Mike Galbraith wrote: >> On Tue, 2015-10-06 at 08:48 +1100, paul.szabo@sydney.edu.au wrote: >>> The Linux CFS scheduler prefers pinned tasks and unfairly >>> gives more CPU time to tasks that have set CPU affinity. >>> This effect is observed with or without CGROUP controls. >>> >>> To demonstrate: on an otherwise idle machine, as some user >>> run several processes pinned to each CPU, one for each CPU >>> (as many as CPUs present in the system) e.g. for a quad-core >>> non-HyperThreaded machine: >>> >>> taskset -c 0 perl -e 'while(1){1}' & >>> taskset -c 1 perl -e 'while(1){1}' & >>> taskset -c 2 perl -e 'while(1){1}' & >>> taskset -c 3 perl -e 'while(1){1}' & >>> >>> and (as that same or some other user) run some without >>> pinning: >>> >>> perl -e 'while(1){1}' & >>> perl -e 'while(1){1}' & >>> >>> and use e.g. top to observe that the pinned processes get >>> more CPU time than "fair".
Interesting, I can reproduce it w/ your simple script. However, they are fair when the number of pinned perl tasks is equal to unpinned perl tasks. I will dig into it more deeply.
Regards, Wanpeng Li
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