Re: Scheduler activations (IIRC) question

[Nick Piggin]

Jamie Lokier wrote:

> Mike Galbraith wrote:
>
> > > The point of the mechanism is to submit system calls in an
> > > asynchronous fashion, after all.  A proper task scheduling is
> > > inappropriate when all we'd like to do is initiate the syscall and
> > > continue processing, just as if it were an async I/O request.
> > Ok, so you'd want a class where you could register an "exception handler" 
> > prior to submitting a system call, and any subsequent schedule would be 
> > treated as an exception?  (they'd have to be nestable exceptions too 
> > right?... <imagines stack explosions> egad:)
>
> Well, apart from not resembling exceptions, and no they don't nest :)

Is it clear that this is a win over having a regular thread to
perform the system call for you? Its obviously a lot more complicated.

I _think_ what you describe is almost exactly what KSE or scheduler
activations in FreeBSD 5 does. I haven't yet seen a test where they
significantly beat regular threads. Although I'm not sure if FreeBSD
uses them for asynchronous syscalls, or just user-space thread
scheduling.


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