On Mon, Mar 13, 2000 at 12:07:41PM +0100, Ingo Molnar wrote:
> On Sun, 12 Mar 2000 firstname.lastname@example.org wrote:
> > > Quite regardless of how you do interrupts: it doesn't matter where youput
> > > the ACK's, you always need to make sure that irq masking etc is correct,
> > > and you must NOT allow a context switch while an interrupt handler is
> > > still running.
> > Ok. Ingo: does your "low latency" patch violate this rule?
> yep, of course. It's a grave error to schedule during IRQ contexts, and we
I think you mean: "of course not"!
> do have an assert in schedule() so it's plain impossible. The lowlatency
> patch simply works by increasing the effective frequency (occurance) of
> rescheduling (preemption) points [without actually rescheduling more
This is too subtle for me. I don't know how you can make true
the first 2 things without having the third be false.
> Having said this, i now do agree that doing a preemptible kernel (which
> the Linux SMP kernel could become with a small amount of work) is a
> superior solution to this, wrt. latencies.
Well, to start, it would violate Linus' rule, an old UNIX rule, and your
new IRQ scheme makes it more complex -- you have to make sure to not
switch out of tasks that are handling unacked interrupts.
I don't know how to trade throughput for latency without losing throughput.
-- --------------------------------------------------------- Victor Yodaiken FSMLabs: www.fsmlabs.com www.rtlinux.com FSMLabs is a servicemark and a service of VJY Associates L.L.C, New Mexico.
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