[dm-devel] default value for rr_min_io too high?

[Christophe Varoqui]

On Sun, Jan 22, 2006 at 05:43:24PM +0000, Alasdair G Kergon wrote:
> On Wed, Jan 18, 2006 at 04:41:57PM -0500, David Wysochanski wrote:
> > I'm wondering where the value of 1000 came from, and
> 
> Thin air.
> 
> > whether that's really a good default.
>  
> Unlikely.
> 
> That's why we made it configurable - to make it easy to try out
> different values and use whatever you find best.
> 
I'm less and less confident we can find good figures, even for a specific workload.
Here is another round of numbers.

Is there still a plan for pluging the elevator in the devmapper device ?
This could help us produce predictable figures (the ones admins like).

Regards,
cvaroqui

Hardware :
- 2x2Gb/s Qlogic HBA
- 1x100GB Vraid1 in a 2C2D EVA3000 StorageWorks array

Test :
- 1 streaming read at a time
- Variations of rr_min_io and dd blocksize

Results :

min_io				dd block size (kB)				
	4	8	16	32	64	128	256	512	1024

8	111	53	51	47	32	59	50	41	61
16	28	79	46	55	112	52	83	68	61
32	41	33	46	31	116	36	75	106	37
64	48	36	67	36	81	54	71	53	47
128	46	46	57	54	66	54	66	59	44
256	56	50	63	63	69	53	57	55	63
512	56	49	55	58	66	60	88	56	57
1024	62	54	70	62	91	82	89	61	61

Script used :
#!/bin/bash

MULTIPATH=/root/foo/multipath/multipath
DEV=/dev/mapper/mpath1
DD="sg_dd sync=1 time=1 dio=1"
SIZE="1024*1024"
MINIO="8 16 32 64 128 256 512 1024"
BS="4 8 16 32 64 128 256 512 1024"

#
# @1 : desired min_io
#
function set_minio
{
        sed s/XX/$1/ /root/multipath.conf > /etc/multipath.conf
        $MULTIPATH $MULTIPATH_OPT >/dev/nul
}

# header
echo "0 $BS"

for minio in $(echo $MINIO)
do
        set_minio $minio
        echo -n "$minio "
        for bs in $(echo $BS)
        do
                count=$(($SIZE/$bs))
                echo -n "$($DD if=$DEV of=/dev/null bs=${bs}k count=${count} 2>&1|head -1|awk '{print $8}') "
        done
        echo
done