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

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Date:	Thu, 22 Feb 2007 11:46:48 -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 Thu, 22 Feb 2007, Evgeniy Polyakov wrote:

> > maybe it will, maybe it wont. Lets try? There is no true difference 
> > between having a 'request structure' that represents the current state 
> > of the HTTP connection plus a statemachine that moves that request 
> > between various queues, and a 'kernel stack' that goes in and out of 
> > runnable state and carries its processing state in its stack - other 
> > than the amount of RAM they take. (the kernel stack is 4K at a minimum - 
> > so with a million outstanding requests they would use up 4 GB of RAM. 
> > With 20k outstanding requests it's 80 MB of RAM - that's acceptable.)
> 
> I tried already :) - I just made a allocations atomic in tcp_sendmsg() and
> ended up with 1/4 of the sends blocking (I counted both allocation
> failure and socket queue overflow). Those 20k blocked requests were
> created in about 20 seconds, so roughly saying we have 1k of thread
> creation/freeing per second - do we want this?

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.




- Davide


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