linux-kernel - Re: threadlets as 'naive pool of threads', epoll, some measurements

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Message-ID: <20070226143201.GB31629@2ka.mipt.ru>
Date:	Mon, 26 Feb 2007 17:32:01 +0300
From:	Evgeniy Polyakov <johnpol@....mipt.ru>
To:	Ingo Molnar <mingo@...e.hu>
Cc:	Davide Libenzi <davidel@...ilserver.org>,
	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>,
	Ulrich Drepper <drepper@...hat.com>,
	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: threadlets as 'naive pool of threads', epoll, some measurements

On Mon, Feb 26, 2007 at 01:50:54PM +0100, Ingo Molnar (mingo@...e.hu) wrote:
> > I feared _ONLY_ situation when thousands of thereads are eating my 
> > brain - so case when 161 threads are running simultanesoulsy is not 
> > that bad compared to what micro-design can do (of its best/worst) at 
> > all!
> 
> even with ten thousand threads it is still pretty fast. Certainly not 
> '10 times slower' as you claimed. And it takes only a single, trivial 
> outer event loop to lift it up to the performance levels of a pure event 
> based server.

I did not claim that it will be 10 times slower, I said that it will be
slower, my '10 times slower', which are actually '15% of hte total time'
is a reply to your 'fast as sync' model, no need to repaing the picture :)

> conclusion: currently i dont see a compelling need for the kevents 
> subsystem. epoll is a pretty nice API and it covers most of the event 
> sources and nicely builds upon our existing poll() infrastructure.
>
> furthermore, i very much contest your claim that a high-performance, 
> highly scalable webserver needs a kevent+nonblock design. Even if i 
> ignore all the obvious usability and maintainance-cost advantages of 
> threadlets.

Ok, I see your point, you insult something you did not ever try to
understand, that is your right.

> > So, caching is good - threadlets do not spawn a new thread, kevent 
> > returns immediately, but in case of things are not that shine - 
> > threadlets spawnd a new thread, while kevent process next request or 
> > waits for all completed.
> 
> no. Please read the evserver_threadlet.c code. There's no kevent in 
> there. There's no epoll() in there. All that you can see there is the 
> natural behavior of pure threadlets. And it's not a workload /I/ picked 
> for threadlets - it is a workload, filesize, parallelism level and 
> request handling function /you/ picked for "event-servers".

I know that there is no kevents there, that would be really strange if
you would test it in your environment after all that empty kevent
releases.

Enough, you say micro-thread design is superior - ok, that is your
point.

> 	Ingo

-- 
	Evgeniy Polyakov
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