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

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Date:	Thu, 22 Feb 2007 11:38:03 -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 Thu, 22 Feb 2007, Ingo Molnar wrote:

> 
> * Ulrich Drepper <drepper@...hat.com> wrote:
> 
> > Ingo Molnar wrote:
> > > in terms of AIO, the best queueing model is i think what the kernel uses 
> > > internally: freely ordered, with barrier support.
> > 
> > Speaking of AIO, how do you imagine lio_listio is implemented?  If 
> > there is no asynchronous syscall it would mean creating a threadlet 
> > for each request but this means either waiting or creating 
> > several/many threads.
> 
> my current thinking is that special-purpose (non-programmable, static) 
> APIs like aio_*() and lio_*(), where every last cycle of performance 
> matters, should be implemented using syslets - even if it is quite 
> tricky to write syslets (which they no doubt are - just compare the size 
> of syslet-test.c to threadlet-test.c). So i'd move syslets into the same 
> category as raw syscalls: pieces of the raw infrastructure between the 
> kernel and glibc, not an exposed API to apps. [and even if we keep them 
> in that category they still need quite a bit of API work, to clean up 
> the 32/64-bit issues, etc.]

Now that chains of syscalls can be way more easily handled with clets^wthreadlets,
why would we need the whole syslets crud inside?
Why can't aio_* be implemented with *simple* (or parallel/unrelated) 
syscall submit w/out the burden of a complex, limiting and heavy API (I 
won't list all the points against syslets, because I already did it 
enough times)? The compat layer only is so bad to not be even funny.
Look at the code. Only removing the syslets crud would prolly cut 40% of 
it. And we did not even touch the compat code yet.



- Davide

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