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

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Message-ID: <20070302102714.GB27687@elf.ucw.cz>
Date:	Fri, 2 Mar 2007 11:27:14 +0100
From:	Pavel Machek <pavel@....cz>
To:	Evgeniy Polyakov <johnpol@....mipt.ru>
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

Hi!

> > > > 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.
> > 
> > Yep? Feel free to rewrite networking to assembly on Eugenix. That
> > should get you 1% improvement. If you reserve few registers to be only
> > used by kernel (not allowed by userspace), you can speedup networking
> > 5%, too. Ouch and you could turn off MMU, that is sure way to get few
> > more percent improvement in your networking case.
> 
> It is not _my_ networking, but taht one you use everyday in every Linux
> box. Notice which tricks are used to remove single byte from
> sk_buff.

Ok, so tricks were worth it in sk_buff case.

> It is called optimization, and if it does us a single plus it must be
> implemented. Not all people have magical fear of new things.

But that does not mean "every optimalization must be
implemented". Only optimalizations that are "worth it" are... 

> > > Using such logic you can just abandon any further development, since it
> > > work as is right now.
> > 
> > Stop trying to pervert my logic.
> 
> Ugh? :)
> I just say in simple words your 'we do not need something if adds 10%,
> but is complex to understand'.

Yes... but that does not mean "stop development". You are still free
to clean up the code _while_ making it faster.

> > If your code is so complex that it is almost impossible to use from
> > userspace, that is good enough reason not to be merged. "But it is 3%
> > faster if..." is not a good-enough argument.
> 
> Is it enough for you?
> 
> epoll           4794.23 req/sec
> kevent          6468.95 req/sec

Maybe. It is not up to me to decide. But "it is faster" is _not_ the
only merge criterium.
									Pavel
-- 
(english) http://www.livejournal.com/~pavelmachek
(cesky, pictures) http://atrey.karlin.mff.cuni.cz/~pavel/picture/horses/blog.html
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