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

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Date:	Thu, 22 Feb 2007 13:59:31 +0100
From:	Ingo Molnar <mingo@...e.hu>
To:	Evgeniy Polyakov <johnpol@....mipt.ru>
Cc:	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>,
	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

* Evgeniy Polyakov <johnpol@....mipt.ru> wrote:

> It is not a TUX anymore - you had 1024 threads, and all of them will 
> be consumed by tcp_sendmsg() for slow clients - rescheduling will kill 
> a machine.

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.)

> My tests show that with 4k connections per second (8k concurrency) 
> more than 20k connections of 80k total block in tcp_sendmsg() over 
> gigabit lan between quite fast machines.

yeah. Note that you can have a million sleeping threads if you want, the 
scheduler wont care. What matters more is the amount of true concurrency 
that is present at any given time. But yes, i agree that overscheduling 
can be a problem.

btw., what is the measurement utility you are using with kevents ('ab' 
perhaps, with a high -c concurrency count?), and which webserver are you 
using? (light-httpd?)

	Ingo
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