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KernelTrap: Kernel Preemption, To Enable Or Not To Enable

Mar 24, 2004, 11:00 (6 Talkback[s])

[ Thanks to Jeremy Andrews for this link. ]

"A recent bug report on the lkml complained of significant performance degradation from enabling CONFIG_PREEMPT, kernel preemption. 2.6 kernel maintainer Andrew Morton pointed out that such degradation from enabling kernel preemption is not normal, instead likely from it triggering a bug. However, an interesting conversation on the merits of kernel preemption followed.

"Andrea Arcangeli, author of the 2.4 virtual memory subsystem, bluntly suggested, 'keep preempt turned off always, it's useless. Preempt just wastes cpu with tons of branches in fast paths that should take one cycle instead.' Andrew Morton noted, 'preempt is overrated.' However, he went on to point out that kernel preemption has been very useful in detecting locking bugs. He added, 'it has been demonstrated that preempt improves the average latency. But not worst-case, because those paths tend to be under spinlock...'"

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