[dm-devel] direct-io regression [Was: How to track down abysmal performance ata - raid1 - crypto - vg/lv - xfs]

[Dominik Brodowski]

On Thu, Aug 05, 2010 at 11:39:43AM -0400, Chris Mason wrote:
> On Thu, Aug 05, 2010 at 05:35:19PM +0200, Dominik Brodowski wrote:
> > On Thu, Aug 05, 2010 at 07:32:40AM -0400, Chris Mason wrote:
> > > But, I'm surprised your drive is doing 8K dio reads at 16MB/s, that
> > > seems a little high.  
> > 
> > Well, that's what it does:
> > 
> > # $ dd if=/dev/mapper/vg0-home_crypt of=/dev/zero iflag=direct bs=8k count=131072 seek=131072
> > # 131072+0 records in
> > # 131072+0 records out
> > # 1073741824 bytes (1.1 GB) copied, 62.0177 s, 17.3 MB/s
> 
> Can I ask you to do the test directly to the real honest to goodness
> drive?   If it were an SSD I'd be less surprised, but then the extra
> submits shouldn't hurt the ssd that much either.

>From lower the chain up to the device:

# LANG=EN dd if=/dev/mapper/vg0-root_crypt of=/dev/zero bs=8k count=131072 seek=393300 iflag=direct
131072+0 records in
131072+0 records out
1073741824 bytes (1.1 GB) copied, 63.1217 s, 17.0 MB/s

# LANG=EN dd if=/dev/mapper/vg0-root of=/dev/zero bs=8k count=131072 seek=393300 iflag=direct
131072+0 records in
131072+0 records out
1073741824 bytes (1.1 GB) copied, 43.2335 s, 24.8 MB/s

# LANG=EN dd if=/dev/sda5 of=/dev/zero bs=8k count=131072 seek=393300 iflag=direct
131072+0 records in
131072+0 records out
1073741824 bytes (1.1 GB) copied, 42.0868 s, 25.5 MB/s

Best,
	Dominik