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

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Message-ID: <20070301150942.GA26025@elte.hu>
Date:	Thu, 1 Mar 2007 16:09:42 +0100
From:	Ingo Molnar <mingo@...e.hu>
To:	Evgeniy Polyakov <johnpol@....mipt.ru>
Cc:	Eric Dumazet <dada1@...mosbay.com>, Pavel Machek <pavel@....cz>,
	Theodore Tso <tytso@....edu>,
	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


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

> > > I can tell you that the problem (at least on my machine) comes from :
> > > 
> > > gettimeofday(&tm, NULL);
> > > 
> > > in evserver_epoll.c
> > 
> > yeah, that's another difference - especially if it's something like 
> > an Athlon64 and gettimeofday falls back to pm-timer, that could 
> > explain the performance difference. That's why i repeatedly asked 
> > Evgeniy to use the /very same/ client function for both the epoll 
> > and the kevent test and redo the measurements. The numbers are still 
> > highly suspect - and we are already down from the prior claim of 
> > kevent being almost twice as fast to a 25% difference.
> 
> There is no gettimeofday() in the running code anymore, and it was 
> placed not in common server processing code btw.
> 
> Ingo, do you really think I will send mails with faked benchmarks? :))

no, i'd not be in this discussion anymore if i thought that. But i do 
think that your benchmark results are extremely sloppy, that make your 
conclusions on them essentially useless.

you were hurling quite colorful and strong assertions into this 
discussion, backed up by these numbers, so you should expect at least 
some minimal amount of scrutiny of those numbers.

> > [...] The numbers are still highly suspect - and we are already down 
> > from the prior claim of kevent being almost twice as fast to a 25% 
> > difference.
>
> Btw, there were never almost twice perfromance increase - epoll in my 
> tests always showed 4-5 thousands requests per second, kevent - up to 
> 7 thausands.

i'm referring to your claim in this mail of yours from 4 days ago for 
example:

  http://lkml.org/lkml/2007/2/25/116

 "But note, that on my athlon64 3500 test machine kevent is about 7900
  requests per second compared to 4000+ epoll, so expect a challenge."

no matter how i look at it, but 7900 is 1.9 times 4000 - which is 
"almost twice".

	Ingo
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