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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: Mikael Abrahamsson <swmike@xxxxxxxxx>
Date: Wed, 4 Aug 2010 13:53:03 +0200 (CEST)
Cc: Dominik Brodowski <linux@xxxxxxxxxxxxxxxxxxxx>, Michael Monnerie <michael.monnerie@xxxxxxxxxxxxxxxxxxx>, linux-raid@xxxxxxxxxxxxxxx, xfs@xxxxxxxxxxx, linux-kernel@xxxxxxxxxxxxxxx, dm-devel@xxxxxxxxxx
In-reply-to: <20100804111803.GA32643@xxxxxxxxxxxxx>
Organization: People's Front Against WWW
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: Alpine 1.10 (DEB 962 2008-03-14)
On Wed, 4 Aug 2010, Christoph Hellwig wrote:

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?

I'm not sure it's that. I have a Core i5 with AES-NI and that didn't significantly increase my overall performance, as it's not there the bottleneck is (at least in my system).

I earlier sent out an email wondering if someone could shed some light on how scheduling, block caching and read-ahead works together when one does disks->md->crypto->lvm->fs, becase that's a lot of layers and potentially a lot of unneeded buffering, readahead and scheduling magic?

--
Mikael Abrahamsson    email: swmike@xxxxxxxxx

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