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

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Date:	Fri, 23 Feb 2007 09:43:14 -0800 (PST)
From:	Davide Libenzi <davidel@...ilserver.org>
To:	Evgeniy Polyakov <johnpol@....mipt.ru>
cc:	Ingo Molnar <mingo@...e.hu>, 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>,
	"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 Fri, 23 Feb 2007, Evgeniy Polyakov wrote:

> On Thu, Feb 22, 2007 at 11:46:48AM -0800, Davide Libenzi (davidel@...ilserver.org) wrote:
> > 
> > A dynamic pool will smooth thread creation/freeing up by a lot.
> > And, in my box a *pthread* create/free takes ~10us, at 1000/s is 10ms, 1%. 
> > Bad, but not so aweful ;)
> > Look, I'm *definitely* not trying to advocate the use of async syscalls for 
> > network here, just pointing out that when we're talking about threads, 
> > Linux does a pretty good job.
>  
> If we are going to create 1000 threads each second, then it is better to
> preallocate them and queue a work to that pool - like syslets did with
> syscalls, but not ulitimately create a new thread just because it is not 
> that slow.

We do create a pool indeed, as I said in the opening of my asnwer. The 
numbers I posted was just to show that thread creation/destroy is pretty 
fast, but that does not justify it as a design choice.



> All such micro-thread designs are especially good in the case when 
> 1. switching is _rare_ (very)
> 2. programmer does not want to create complex model to achieve maximum
> performance
> 
> Disk (cached) IO definitely hits first entry and second one is there for
> advertisements and fast deployment, but overall usage of the
> asynchronous IO model is not limited to the above scenario, so
> micro-threads definitely hit own niche, but they can not cover all usage
> cases.

You know, I read this a few times, but I still don't get what your point 
is here ;) Are you talking about micro-thread design in the kernel as for 
kthreads usage for AIO, or about userspace?



- Davide


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