Re: [9fans] system responsiveness

["Russ Cox" <rsc@plan9.bell-labs.com>]

> I don't recall the details, but while I was playing with
> the scheduler last fall Russ and I found that there was a
> bug with assigning priorities.  Under load the scheduler
> was a real dog; I think Russ subsequently fixed it.  Doing

Presotto put some tweaks in for me.  The processes move
around dynamically (between priority levels) a bit more now.
My particular test case was an mp3 encoder, which yielded the
processor to go to disk just often enough that it wasn't being
penalized for using so much CPU.  The scheduler is more responsive
now to long-term CPU hogs that occasionally schedule, so that
background tasks like mp3enc won't hurt your interactive
performance as much.

> so made the system noticeably snappier.  I also ran into
> some problems with what appeared to be lost clock
> interrupts, but never had the time to track things down
> completely.

This is a really cool bug.  The system would just stop
scheduling other processes, but if you moved the mouse
around that would generate enough interrupts that the
preemptive scheduler would go into effect and get you
going.  Stop the moving the mouse, stop making progress.
We never found it, and all that has been rewritten recently
so maybe it got fixed inadvertently.

Russ