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

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Date:	Thu, 22 Feb 2007 07:51:25 +0100
From:	Ingo Molnar <mingo@...e.hu>
To:	"Michael K. Edwards" <medwards.linux@...il.com>
Cc:	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>,
	Ulrich Drepper <drepper@...hat.com>,
	Zach Brown <zach.brown@...cle.com>,
	Evgeniy Polyakov <johnpol@....mipt.ru>,
	"David S. Miller" <davem@...emloft.net>,
	Suparna Bhattacharya <suparna@...ibm.com>,
	Davide Libenzi <davidel@...ilserver.org>,
	Jens Axboe <jens.axboe@...cle.com>,
	Thomas Gleixner <tglx@...utronix.de>
Subject: Re: [patch 00/13] Syslets, "Threadlets", generic AIO support, v3


* Michael K. Edwards <medwards.linux@...il.com> wrote:

> [...] As for threadlets, making them kernel threads is not such a good 
> design feature, O(1) scheduler or not.  You take the full hit of 
> kernel task creation, on the spot, for every threadlet that blocks. 
> [...]

this is very much not how they work. Threadlets share the same basic 
infrastructure with syslets and they do /not/ take a 'full hit of kernel 
thread creation' when they block. Please read the announcements, past 
discussions on lkml and the code about how it works.

about your other point:

> > threadlets, when they block, are regular kernel threads, so the 
> > regular O(1) scheduler takes care of them. If MMU trashing is of any 
> > concern then syslets should be used to implement the most 
> > performance-critical events: under Linux a kernel thread that does 
> > not exit out to user-space does not do any TLB switching at all. 
> > (even if there are multiple processes active and their syslets 
> > intermix)
> 
> As far as I am concerned syslets by themselves are a dead letter, 
> because you can't do any of the things that potential application 
> coders need to do with them. [...]

syslets are not meant to be directly exposed to application coders. 
Syslets (like many of my previous mails stated) are meant as building 
blocks to higher-level AIO interfaces such as in glibc or libaio. Then 
user-space can build its state-machine based on syslet-implemented 
glibc/libaio. In that specific role they are a very fast and scalable 
mechanism.

	Ingo
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