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Date: Sun, 17 Aug 2003 17:05:34 +1000
From: Nick Piggin <piggin@cyberone.com.au>
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To: Jamie Lokier <jamie@shareable.org>
CC: Mike Galbraith <efault@gmx.de>, Con Kolivas <kernel@kolivas.org>,
       linux kernel mailing list <linux-kernel@vger.kernel.org>,
       Andrew Morton <akpm@osdl.org>, Ingo Molnar <mingo@elte.hu>,
       gaxt <gaxt@rogers.com>
Subject: Re: Scheduler activations (IIRC) question
References: <5.2.1.1.2.20030816080614.01a0e418@pop.gmx.net> <20030815235431.GT1027@matchmail.com> <200308160149.29834.kernel@kolivas.org> <20030815230312.GD19707@mail.jlokier.co.uk> <20030815235431.GT1027@matchmail.com> <5.2.1.1.2.20030816080614.01a0e418@pop.gmx.net> <5.2.1.1.2.20030817072115.0198f398@pop.gmx.net> <20030817065501.GA1105@mail.jlokier.co.uk>
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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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