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

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Message-ID: <20070227184906.GB3733@kernel.dk>
Date:	Tue, 27 Feb 2007 19:49:06 +0100
From:	Jens Axboe <jens.axboe@...cle.com>
To:	Avi Kivity <avi@...o.co.il>
Cc:	Ingo Molnar <mingo@...e.hu>, suparna@...ibm.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)

On Tue, Feb 27 2007, Avi Kivity wrote:
> Ingo Molnar wrote:
> >* Avi Kivity <avi@...o.co.il> wrote:
> >
> >  
> >>But what about cpu usage?  At these low levels, the cpu is probably 
> >>underutilized.  It would be interesting to measure cpu time per I/O 
> >>request (or, alternatively, use an I/O subsystem that can saturate the 
> >>processors).
> >>    
> >
> >yeah - that's what testing on ramdisk (Jens') or on a loopback block 
> >device (mine) approximates to a certain degree.
> >
> >  
> 
> Ramdisks or fully cached loopback return immediately, so cache thrashing 
> effects don't show up.
> 
> Maybe a device mapper delay target or nbd + O_DIRECT can insert delays 
> to make the workload more disk-like.

Take a look at scsi-debug, it can do at least some of that.

-- 
Jens Axboe

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