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SubjectRe: new IRQ scalability changes in 2.3.48

On Mon, 13 Mar 2000, Linus Torvalds wrote:

> We want to avoid having long latencies, and we can easily get that by
> just allowing timer interrupts to schedule which we're in a big
> "memcpy_to_user()" and we don't hold any kernel lock etc. No need to
> try to be clever at lock release time - if we get a pending
> reschedule, we might as well leave it pending, it's going to be
> serviced soon enough anyway.

yep - and the 'natural blocking' of memcpys is bound (in size) anyway, so
the conditional reschedule is probably faster (and an already proven
solution). I believe there is one more reason to allow a memcpy to finish
before rescheduling: the source buffer is often (especially in the
networking case) already cached, so we are better off if we wait 100 usecs
and reschedule _after_ the memcpy.


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