Re: Low latency for recent kernels

Glendon Gross
2002-01-24T04:21:30Z

Is this patch available for 2.5.2 ? or is it already part of the tree?

On 23 Jan 2002, Robert Love wrote:

> On Wed, 2002-01-23 at 22:48, Dan Maas wrote:
>
> > Two situations where I would expect low-latency/preemption to have a
> > positive effect on responsiveness are 1) when the system is under heavy CPU
> > and disk load (e.g. kernel compile); due to the interactive tasks being able
> > to run earlier/more often, and 2) when performing UI operations that depend
> > on tight synchronization between X/the WM/the X client, particularly opaque
> > window resizing. (my theory is that low-latency/preemption results in the
> > CPU switching more rapidly or evenly among these processes, reducing the
> > perceptible "lag" between the client window and its WM frame)
>
> This is exactly the area preempt/low-latency helps and I think your
> theory is pretty much dead on.
>
> With preempt-kernel, ideally, an interactive task finds itself runnable
> like this: user event causes interrupt, interrupt sets need_resched, on
> return from interrupt we cause a preemption of current task (which can
> happen whether task is in kernel or userland, now), and schedule the
> interactive task onto the CPU.
>
> This leads to better scheduling fairness and short scheduling latency.
>
> If you or Havoc are interested in any tests or further work with the
> preemptive kernel, I'd be more than willing. Hey, I use GNOME ;)
>
> Robert Love
>
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