Re: [PATCH 2 of 4] Introduce i386 fibril scheduling

[Linus Torvalds]

On Fri, 2 Feb 2007, Linus Torvalds wrote: 
> On Fri, 2 Feb 2007, Ingo Molnar wrote:
> > 
> > but if the application /has/ identified fundamental parallelism, we 
> > /must not/ shut that parallelism off by /designing/ this interface to 
> > use the fibril thing which is a limited cooperative, single-CPU entity. 
> 
> Right. We should for example encourage people to use some kind of 
> paralellizing construct. 
> 
> I know! We could even call them "threads", so to give people the idea that 
> they are independent smaller entities in a thicker "rope", and we could 
> call that bigger entity a "task" or "process", since it "processes" data.
> 
> Or is that just too far out?

So the above was obviously tongue-in-cheek, but you should really think 
about the context here.

We're discussing doing *single* system calls. There is absolutely zero 
point to try to parallelize the work over multiple CPU's or threads. We're 
literally talking about doing things where the actual CPU cost is in the 
hundreds of nanoseconds, and where traditionally a rather noticeable part 
of the cost is not the code itself, but the high cost of taking a system 
call trap, and saving all the register state.

When parallelising "real work", I absolutely agree with you: we should use 
threads. But you need to look at what it is we parallelize here, and ask 
yourself why we're doing what we're doing, and why people aren't *already* 
just using a separate thread for it.

			Linus
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