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

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Date:	Thu, 22 Feb 2007 15:36:58 +0100
From:	Ingo Molnar <mingo@...e.hu>
To:	Suparna Bhattacharya <suparna@...ibm.com>
Cc:	Evgeniy Polyakov <johnpol@....mipt.ru>,
	Ulrich Drepper <drepper@...hat.com>,
	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>,
	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


* Suparna Bhattacharya <suparna@...ibm.com> 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.)
> 
> At what point are the cachemiss threads destroyed ? In other words how 
> well does this adapt to load variations ? For example, would this 80MB 
> of RAM continue to be locked down even during periods of lighter loads 
> thereafter ?

you can destroy them at will from user-space too - just start a slow 
timer that zaps them if load goes down. I can add a 
sys_async_thread_exit(nr_threads) API to be able to drive this without 
knowing the TIDs of those threads, and/or i can add a kernel-internal 
mechanism to zap inactive threads. It would be rather easy and 
low-overhead - the v2 code already had a max_nr_threads tunable, i can 
reintroduce it. So the size of the pool of contexts does not have to be 
permanent at all.

	Ingo
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