Messages in this thread | | | Subject | Re: SMP Scheduling | Date | Mon, 09 Aug 1999 00:25:12 -0400 | From | Horst von Brand <> |
| |
Peter Waltenberg <peterw@dascom.com> said: > On 09-Aug-99 Horst von Brand wrote: > > Peter Waltenberg <peterw@dascom.com> said: > > [...]
> >> Under 2.2 you see that one CPU hog hopping CPU's and at regular > >> intervals. Using xosview to track load what you see is a picket fence > >> effect. And there are more than "3 processes" running, more like 80 > >> on my machine, so running xosview alone shouldn't be enough to force > >> this to happen and if it were, the other processes should be > >> introducing enough noise to make the CPU swapping more erratic.
> > If you have that many processes running, your hog will have its state at > > the CPU flushed anyway, so the CPU selected is irrelevant.
> >> This does seem to be "wrong", not so much that the process is changing > >> CPU's, thats reasonable, but the fact that it's doing it with such > >> regularity now.
> > File it under "random trivia" then ;-)
> I'd expect the process to be flushed, however in that case I'd expect it > to be re-run on some random CPU. However that doesn't seem to happen, the > process swaps CPU's at REGULAR intervals. The scheduler is supposedly > designed so that a process will have a tendency to run on the same CPU.
This tendency is for a time quantum only, what you are seeing is clearly at a much larger timescale. And the other processes will also tend to stick to the same CPU, I can very well imagine that with the right mix this gives wandering processes when you use round-robin scheduling. Essentially the explanation given for three processes, just longer ;-)
> It's not that the process changes CPU's, it's that it's doing it at > regular intervals that I find worrying. > Yes, that could just be coincidence, or it could be a real problem.
AFAIKS, if you see the effect, it is at a timescale of seconds. An unneeded migration a second is not that big a deal, is it? -- Horst von Brand vonbrand@sleipnir.valparaiso.cl Casilla 9G, Viña del Mar, Chile +56 32 672616
- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.rutgers.edu Please read the FAQ at http://www.tux.org/lkml/
| |