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SubjectRe: [2.4.17/18pre] VM and swap - it's really unusable
On Tue, 2002-01-08 at 15:59, Daniel Phillips wrote:

> And while I'm enumerating differences, the preemptable kernel (in this
> incarnation) has a slight per-spinlock cost, while the non-preemptable kernel
> has the fixed cost of checking for rescheduling, at intervals throughout all
> 'interesting' kernel code, essentially all long-running loops. But by clever
> coding it's possible to finesse away almost all the overhead of those loop
> checks, so in the end, the non-preemptible low-latency patch has a slight
> efficiency advantage here, with emphasis on 'slight'.

True (re spinlock weight in preemptible kernel) but how is that not
comparable to explicit scheduling points? Worse, the preempt-kernel
typically does its preemption on a branch on return to interrupt
(similar to user space's preemption). What better time to check and
reschedule if needed?

Robert Love

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