Re: Minutes from Feb 21 LSE Call

Bill Huey
2003-02-24T10:04:39Z

On Mon, Feb 24, 2003 at 01:56:25AM -0800, Andrew Morton wrote:
> But that is speculation as well - I never observed this aspect to be
> a real problem. Probably, it was not.
>
> Substantiation of your claim requires quality testing and a plausible
> explanation. I do not believe we have seen either, OK?

Well, let's back off here. It's not my claim, it's Robert Love's in that
URL. Not to arrange a fight, but I had to point that out. :)

> > http://linuxdevices.com/articles/AT6106723802.html
>
> I did, briefly. It appears to be claiming that the average scheduling
> latency of the non-preemptible kernel is ten milliseconds!

They mention that this is related to the console code. Obviously, if you're
not checking for reschedule in a big pix map scroll blit, then it's going
to stick out boldly as a big latency spike.

A fully preemptive system would only turn off preemption in places that
would break drivers and other obvious places like scheduler run-queues,
etc...

> Maybe I need to read that again in the morning.

It's also an old article, but goes over a lot of the basics of a fully
preemptable kernel like that. Things might not be as dramatic now with
2.5.62. Not sure how things are now...

bill