linux-kernel - Re: [patch 00/13] Syslets, "Threadlets", generic AIO support, v3

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Date:	Wed, 28 Feb 2007 13:46:09 -0800 (PST)
From:	Davide Libenzi <davidel@...ilserver.org>
To:	Ingo Molnar <mingo@...e.hu>
cc:	Ulrich Drepper <drepper@...hat.com>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Arjan van de Ven <arjan@...radead.org>,
	Christoph Hellwig <hch@...radead.org>,
	Andrew Morton <akpm@....com.au>,
	Alan Cox <alan@...rguk.ukuu.org.uk>,
	Zach Brown <zach.brown@...cle.com>,
	Evgeniy Polyakov <johnpol@....mipt.ru>,
	"David S. Miller" <davem@...emloft.net>,
	Suparna Bhattacharya <suparna@...ibm.com>,
	Jens Axboe <jens.axboe@...cle.com>,
	Thomas Gleixner <tglx@...utronix.de>
Subject: Re: [patch 00/13] Syslets, "Threadlets", generic AIO support, v3

On Wed, 28 Feb 2007, Ingo Molnar wrote:

> * Davide Libenzi <davidel@...ilserver.org> wrote:
> 
> > Did you hide all the complexity of the userspace atom decoding inside 
> > another function? :)
> 
> no, i made the 64-bit and 32-bit structures layout-compatible. This 
> makes the 32-bit structure as large as the 64-bit ones, but that's not a 
> big issue, compared to the simplifications it brings.

Do you have a new version to review?



> > > But i'm happy to change the syslet API in any sane way, and did so 
> > > based on feedback from Jens who is actually using them.
> > 
> > Wouldn't you agree on a simple/parallel execution engine [...]
> 
> the thing is, there's almost zero overhead from having those basic 
> things like conditions and the ->next link, and they make it so much 
> more capable. As usual my biggest problem is that you are not trying to 
> use syslets at all - you are only trying to get rid of them ;-) My 
> purpose with syslets is to enable a syslet to do almost anything that 
> user-space could do too, as simply as possible. Syslets could even 
> allocate user-space memory and then use it (i dont think we actually 
> want to do that though). That doesnt mean arbitrary complex code 
> /should/ be done via syslets, or that it wont be significantly slower 
> than what user-space can do, but i'd not like to artificially dumb the 
> engine down. I'm totally willing to simplify/shrink the vectoring of 
> arguments and just about anything else, but your proposals so far (such 
> as your return-value-embedded-in-atom suggestion) all kill important 
> aspects of the engine.

Ok, we're past the error code in the atom, as Linus pointed out ;)
How about this, with async_wait returning asynid's back to a userspace 
ring buffer?

struct syslet_utaom {
        long *result;
        unsigned long asynid;
        unsigned long nr_sysc;
        unsigned long params[8];
};

My problem with the syslets in their current form is, do we have a real 
use for them that justify the extra complexity inside the kernel? Or with 
a simple/parellel async submission, coupled with threadlets, we can cover 
a pretty broad range of real life use cases?



- Davide


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