Re: [openbeos] Re: GSoC ticket #1069 (thread scheduler) application

On 2007-04-10 at 21:33:28 [+0200], André Braga <[email protected]> wrote:
> On 4/10/07, Ingo Weinhold <bonefish-CFLBMwTPW48UNGrzBIF7/[email protected]> wrote:
[...]
> > IMHO, a GA approach is over the top, as is your
> > specialized memory allocator idea.
> 
> GA, definitely. A memory allocator is not that over the top, IMO; it's
> all about having a contiguous memory space and putting related memory
> objects close together and hopefully bring them into the cache at the
> same time. But that's just an optimization -- one that would
> potentially save thousands of cycles, may I add --, it's not even
> close to being essential.

We're planing to have a slab allocator for our kernel anyway. If your 
stuctures end up being small enough (i.e. smaller than a cache line; in case 
of per-thread data you'd obviously have to separate them from struct thread 
then) you can simply use a separate cache, which will result in exactly the 
locality you're looking for.

> > Regarding memory usage, I think it's not that much of an issue. While it's
> > generally prudent to have an eye on kernel memory usage, a few bytes more
> > in struct thread won't be a problem -- even with thousand threads (a 
> > rather
> > unusual case I'd say) it's only some KB after all.
> 
> You just touched on the question I was intending to ask next... What
> is the realistic number of threads expected to be present on a typical
> BeOS system? I don't know how typical my system would be, so I guess
> I'd better run an informal poll here...

I don't think it's usually more than a few hundred threads. I'd be surprised, 
if I ever managed to have more than 1000 threads at the same time. The hard 
limit under BeOS is 4096; IMHO completely sufficient.

CU, Ingo

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