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The long road to lazy preemption in the Linux CPU scheduler

(lwn.net)
218 points chmaynard | 2 comments | 19 Oct 24 07:29 UTC | HN request time: 0s | source
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weinzierl ◴[19 Oct 24 09:11 UTC] No.41886648[source]▶
"Current kernels have four different modes that regulate when one task can be preempted in favor of another"

Is this about kernel tasks, user tasks or both?

replies(2): >>41886784 #>>41886832 #
GrayShade ◴[19 Oct 24 09:44 UTC] No.41886784[source]▶
Kernel code, user-space code is always preemptible.
replies(1): >>41887715 #
1. fguerraz ◴[19 Oct 24 13:40 UTC] No.41887715[source]▶
Not true when the user-space thread has RT priority.
replies(1): >>41887763 #
2. temac ◴[19 Oct 24 13:51 UTC] No.41887763[source]▶
RT threads can be prempted by higher prio RT, and IIRC some kernel threads run at the highest prio. Plus you can be prempted by SMI, an hypervisor, etc