linux-kernel - Re: A quick fio test (was Re: [patch 00/13] Syslets, "Threadlets", generic AIO support, v3)

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Message-ID: <20070226141808.GB24683@elte.hu>
Date:	Mon, 26 Feb 2007 15:18:09 +0100
From:	Ingo Molnar <mingo@...e.hu>
To:	Suparna Bhattacharya <suparna@...ibm.com>
Cc:	Jens Axboe <jens.axboe@...cle.com>, 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>,
	Evgeniy Polyakov <johnpol@....mipt.ru>,
	"David S. Miller" <davem@...emloft.net>,
	Davide Libenzi <davidel@...ilserver.org>,
	Thomas Gleixner <tglx@...utronix.de>
Subject: Re: A quick fio test (was Re: [patch 00/13] Syslets, "Threadlets", generic AIO support, v3)


* Suparna Bhattacharya <suparna@...ibm.com> wrote:

> > syslet still on top. Measuring O_DIRECT reads (of 4kb size) on ramfs 
> > with 100 processes each with a depth of 200, reading a per-process 
> > private file of 10mb (need to fit in my ram...) 10 times each. IOW, 
> > doing 10,000MiB of IO in total:
> 
> But, why ramfs ? Don't we want to exercise the case where O_DIRECT 
> actually blocks ? Or am I missing something here ?

ramfs is just the easiest way to measure the pure CPU overhead of a 
workload without real IO delays (and resulting idle time) getting in the 
way. It's certainly not the same thing, but still it's pretty useful 
most of the time. I used a different method, loopback block device, and 
got similar results. [ Real IO shows similar results as well, but is a 
lot more noisy and hence harder to interpret (and thus easier to get 
wrong). ]

	Ingo
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