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Re: direct-io regression [Was: How to track down abysmal performance ata

To: Jeff Moyer <jmoyer@xxxxxxxxxx>
Subject: Re: direct-io regression [Was: How to track down abysmal performance ata - raid1 - crypto - vg/lv - xfs]
From: Chris Mason <chris.mason@xxxxxxxxxx>
Date: Thu, 5 Aug 2010 15:01:38 -0400
Cc: Dominik Brodowski <linux@xxxxxxxxxxxxxxxxxxxx>, Valdis.Kletnieks@xxxxxx, josef@xxxxxxxxxx, Michael Monnerie <michael.monnerie@xxxxxxxxxxxxxxxxxxx>, Christoph Hellwig <hch@xxxxxxxxxxxxx>, linux-raid@xxxxxxxxxxxxxxx, xfs@xxxxxxxxxxx, linux-kernel@xxxxxxxxxxxxxxx, dm-devel@xxxxxxxxxx
In-reply-to: <x49tyn8c2ea.fsf@xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx>
Mail-followup-to: Chris Mason <chris.mason@xxxxxxxxxx>, Jeff Moyer <jmoyer@xxxxxxxxxx>, Dominik Brodowski <linux@xxxxxxxxxxxxxxxxxxxx>, Valdis.Kletnieks@xxxxxx, josef@xxxxxxxxxx, Michael Monnerie <michael.monnerie@xxxxxxxxxxxxxxxxxxx>, Christoph Hellwig <hch@xxxxxxxxxxxxx>, linux-raid@xxxxxxxxxxxxxxx, xfs@xxxxxxxxxxx, linux-kernel@xxxxxxxxxxxxxxx, dm-devel@xxxxxxxxxx
References: <20100804085039.GA11671@xxxxxxxxxxxxx> <20100804091317.GA27779@xxxxxxxxxxxxxxxxxx> <20100804092122.GA2998@xxxxxxxxxxxxx> <20100804073546.GA7494@xxxxxxxxxxxxxxxxxxxxxxxxxx> <201008041116.09822@xxxxxx> <20100804102526.GB13766@xxxxxxxxxxxxxxxxxx> <15446.1280953986@localhost> <20100805093100.GA3001@xxxxxxxxxxxxxxxxxxxxxxxxxx> <20100805113240.GA29846@think> <x49tyn8c2ea.fsf@xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx>
User-agent: Mutt/1.5.20 (2009-06-14)
On Thu, Aug 05, 2010 at 02:58:37PM -0400, Jeff Moyer wrote:
> Chris Mason <chris.mason@xxxxxxxxxx> writes:
> 
> > But, I'm surprised your drive is doing 8K dio reads at 16MB/s, that
> > seems a little high.  
> 
> I'm not sure why you think that.  We're talking about a plain old SATA
> disk, right?  I can get 40-50MB/s on my systems for 8KB O_DIRECT reads.
> What am I missing?

Clearly I'm wrong, his drive is going much faster ;)  I expect the
smaller reads to be slower but the drive's internal cache is doing well.

-chris

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