Re: [patch 00/13] Syslets, "Threadlets", generic AIO support, v3
From: Al Boldi
Date: Sun Feb 25 2007 - 14:08:39 EST
Ingo Molnar wrote:
> now look at kevents as the queueing model. It does not queue 'tasks', it
> lets user-space queue requests in essence, in various states. But it's
> still the same conceptual thing: a memory buffer with some state
> associated to it. Yes, it has no legacies, it has no priorities and
> other queueing concepts attached to it ... yet. If kevents got
> mainstream, it would get the same kind of pressure to grow 'more
> advanced' event queueing and event scheduling capabilities.
> Prioritization would be needed, etc.
But it would probably be tuned specifically to its use case, which would mean
inherently better performance.
> So my fundamental claim is: a kernel thread /is/ our main request
> structure. We've got tons of really good system calls that queue these
> 'requests' around the place and offer functionality around this concept.
> Plus there's a 1.2+ billion lines of Linux userspace code that works
> well with this abstraction - while there's nary a few thousand lines of
> event-based user-space code.
Think of the kernel scheduler as a default fallback scheduler, for procs that
are randomly queued. Anytime you can identify a group of procs/threads that
behave in a similar way, it's almost always best to do specific/private
scheduling, for performance reasons.
> I also say that you'll likely get kevents outperform threadlets. Maybe
> even significantly so under the right conditions. But i very much
> believe we want to get similar kind of performance out of thread/task
> scheduling, and not introduce a parallel framework to do request
> scheduling the hard way ... just because our task concept and scheduling
> implementation got too fat. For the same reason i didnt really like
> fibrils: they are nice, and Zach's core idea i think nicely survived in
> the syslet/threadlet model too, but they are more limited than true
> threads. So doing that parallel infrastructure, which really just
> implements the same, and is only faster because it skips features, would
> just be hiding the problem with our primary abstraction. Ok?
Ok. But what you are proposing here is a dynamically plugable scheduler that
is extensible on top of that.
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