Messages in this thread |  | | Subject | Re: [2.4.17/18pre] VM and swap - it's really unusable | From | Robert Love <> | Date | 08 Jan 2002 16:17:32 -0500 |
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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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