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Re: How to track down abysmal performance ata - raid1 - crypto - vg/lv -

To: Christoph Hellwig <hch@xxxxxxxxxxxxx>
Subject: Re: How to track down abysmal performance ata - raid1 - crypto - vg/lv - xfs
From: Dominik Brodowski <linux@xxxxxxxxxxxxxxxxxxxx>
Date: Wed, 4 Aug 2010 13:24:28 +0200
Cc: Michael Monnerie <michael.monnerie@xxxxxxxxxxxxxxxxxxx>, linux-raid@xxxxxxxxxxxxxxx, xfs@xxxxxxxxxxx, linux-kernel@xxxxxxxxxxxxxxx, dm-devel@xxxxxxxxxx
In-reply-to: <20100804111803.GA32643@xxxxxxxxxxxxx>
Mail-followup-to: Dominik Brodowski <linux@xxxxxxxxxxxxxxxxxxxx>, Christoph Hellwig <hch@xxxxxxxxxxxxx>, Michael Monnerie <michael.monnerie@xxxxxxxxxxxxxxxxxxx>, linux-raid@xxxxxxxxxxxxxxx, xfs@xxxxxxxxxxx, linux-kernel@xxxxxxxxxxxxxxx, dm-devel@xxxxxxxxxx
References: <20100804073546.GA7494@xxxxxxxxxxxxxxxxxxxxxxxxxx> <20100804085039.GA11671@xxxxxxxxxxxxx> <20100804091317.GA27779@xxxxxxxxxxxxxxxxxx> <20100804092122.GA2998@xxxxxxxxxxxxx> <20100804073546.GA7494@xxxxxxxxxxxxxxxxxxxxxxxxxx> <201008041116.09822@xxxxxx> <20100804102526.GB13766@xxxxxxxxxxxxxxxxxx> <20100804111803.GA32643@xxxxxxxxxxxxx>
User-agent: Mutt/1.5.18 (2008-05-17)
On Wed, Aug 04, 2010 at 07:18:03AM -0400, Christoph Hellwig wrote:
> On Wed, Aug 04, 2010 at 12:25:26PM +0200, Dominik Brodowski wrote:
> > Hey,
> > 
> > many thanks for your feedback. It seems the crypto step is the culprit:
> > 
> > Reading 1.1 GB with dd, iflag=direct, bs=8k:
> > 
> > /dev/sd*                35.3 MB/s       ( 90 %)
> > /dev/md*                39.1 MB/s       (100 %)
> > /dev/mapper/md*_crypt    3.9 MB/s       ( 10 %)
> > /dev/mapper/vg1-*        3.9 MB/s       ( 10 %)
> > 
> > The "good" news: it also happens on my notebook, even though it has a
> > different setup (no raid, disk -> lv/vg -> crypt). On my notebook, I'm
> > more than happy to test out different kernel versions, patches etc.
> > 
> > /dev/sd*                17.7 MB/s       (100 %)
> > /dev/mapper/vg1-*       16.2 MB/s       ( 92 %)
> > /dev/mapper/*_crypt      3.1 MB/s       ( 18 %)
> 
> The good news is that you have it tracked down, the bad news is that
> I know very little about dm-crypt.  Maybe the issue is the single
> threaded decryption in dm-crypt?  Can you check how much CPU time
> the dm crypt kernel thread uses?

2 CPUs overall:
Cpu(s):  1.0%us,  5.7%sy,  0.0%ni, 44.8%id, 47.0%wa,  0.0%hi,  1.5%si, 0.0%st

Thanks & best,
        Dominik

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