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

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Date:	Thu, 1 Mar 2007 12:47:23 +0300
From:	Evgeniy Polyakov <johnpol@....mipt.ru>
To:	Pavel Machek <pavel@....cz>
Cc:	Theodore Tso <tytso@....edu>, Ingo Molnar <mingo@...e.hu>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Ulrich Drepper <drepper@...hat.com>,
	linux-kernel@...r.kernel.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

On Thu, Mar 01, 2007 at 10:26:34AM +0100, Pavel Machek (pavel@....cz) wrote:
> > > 10% gain in speed is NOT worth major complexity increase.
> > 
> > Should I create a patch to remove rb-tree implementation?
> 
> If you can replace them with something simpler, and no worse than 10%
> slower in worst case, then go ahead. (We actually tried to do that at
> some point, only to realize that efence stresses vm subsystem in very
> unexpected/unfriendly way).

Agh, only 10% in the worst case.
I think you can not even imagine what tricks network uses to get at
least aditional 1% out of the box.
Using such logic you can just abandon any further development, since it
work as is right now.

> > That practice is stupid IMO.
> 
> Too bad. Now you can start Linux fork called Eugenix.
> 
> (But really, Linux is not "maximum performance at any cost". Linux is
> "how fast can we get that while keeping it maintainable?").

Should I read it like: we do not understand what it is and thus we do
not want it?

> That is why, while arguing syslets vs. kevents, you need need to argue
> not "kevents are faster because they avoid context switch overhead",
> but "kevents are _so much_ faster that it is worth the added
> complexity". And Ingo seems to showing you they are not _so much_
> faster.

Threadlets behave much worse without event driven model, events can
behave worse without backed threads, they are mutually compensating.

I posted kevent/epoll benchmarks and related design issues too many 
times both with handmade applications (which might be broken as hell)
and popular open-source servers to repeat them again.

> 									Pavel
> -- 
> (english) http://www.livejournal.com/~pavelmachek
> (cesky, pictures) http://atrey.karlin.mff.cuni.cz/~pavel/picture/horses/blog.html

-- 
	Evgeniy Polyakov
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