[dm-devel] How to track down abysmal performance ata - raid1 - crypto - vg/lv - xfs
Dominik Brodowski
linux at dominikbrodowski.net
Wed Aug 4 11:24:28 UTC 2010
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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