Re: Scheduler activations (IIRC) question

[Nick Piggin <piggin@cyberone.com.au>]

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.