linux-kernel - Re: AIO, FIO and Threads ...

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Message-ID: <20070321074014.GD14389@kernel.dk>
Date:	Wed, 21 Mar 2007 08:40:14 +0100
From:	Jens Axboe <jens.axboe@...cle.com>
To:	Davide Libenzi <davidel@...ilserver.org>
Cc:	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	Ingo Molnar <mingo@...e.hu>,
	Linus Torvalds <torvalds@...ux-foundation.org>
Subject: Re: AIO, FIO and Threads ...

On Tue, Mar 20 2007, Davide Libenzi wrote:
> 
> I was looking at Jens FIO stuff, and I decided to cook a quick patch for 
> FIO to support GUASI (Generic Userspace Asyncronous Syscall Interface):
> 
> http://www.xmailserver.org/guasi-lib.html
> 
> I then ran a few tests on my Dual Opteron 252 with SATA drives (sata_nv) 
> and 8GB of RAM.
> Mind that I'm not FIO expert, like at all, but I got some interesting 
> results when comparing GUASI with libaio at 8/1000/10000 depths.
> If I read those result correctly (Jens may help), GUASI output is more 
> then double the libaio one.
> Lots of context switches, yes. But the throughput looks like 2+ times.
> Can someone try to repeat the measures and/or spot the error?
> Or tell me which other tests to run?
> This is kinda a suprise for me ...

I don't know guasi at all, but libaio requires O_DIRECT to be async. I'm
sure you know this, but you may not know that fio default to buffered IO
so you have to tell it to use O_DIRECT :-)

So try adding a --direct=1 (or --buffered=0, same thing) as an extra
option when comparing depths > 1.

I'll add your guasi engine, but disable it. Unfortunately fio still
doesn't have a nifty configure setup, so these things are still
manual...

-- 
Jens Axboe

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