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

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Message-ID: <20070227161617.GA16774@elte.hu>
Date:	Tue, 27 Feb 2007 17:16:17 +0100
From:	Ingo Molnar <mingo@...e.hu>
To:	Avi Kivity <avi@...o.co.il>
Cc:	suparna@...ibm.com, 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)


* Avi Kivity <avi@...o.co.il> wrote:

> > 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.

even fully cached loopback schedules the loopback kernel thread - but i 
agree that it's inaccurate: hence the 'approximates to a certain 
degree'.

> Maybe a device mapper delay target or nbd + O_DIRECT can insert delays 
> to make the workload more disk-like.

yeah. I'll hack a small timeout into loopback requests i think. But then 
real disk-platter effects are left out ... so it all comes down to 
eventually having to try it on real disks too :)

	Ingo
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