[ewg] SRP performance in SCST

[Doron Shoham]

Hi,

I'm trying to test SRP performance in SCST.

I used the following configuration:
Both, target and initiator are x86-64 machines.
Both have OFED-1.3 GA installed.
The HCAs are 20 Gb/sec (4X DDR).

Target:
Sles 10.
4GB RAM
srpt installed.
SCST installed.

Initiator:
Redhat 5.
2GB RAM.
srp initiator (from OFED) is installed.

On the target I set a virtual device:
dd if=/dev/zero of=/tmp/tempfile bs=64k count=100
echo "open vdisk0 /tmp/tempfile NULLIO" > /proc/scsi_tgt/vdisk/vdisk
echo "add vdisk0 0" > /proc/scsi_tgt/groups/Default/devices
cat /proc/scsi_tgt/vdisk/vdisk
Name              Size(MB)    Block size  Options         File name
vdisk0            1572864     512         NIO             /tmp/tempfile


I used the following commands:
for write commands:
sgp_dd of=/dev/sg1 if=/dev/zero bs=512 bpt=<from 2-512> thr=8 time=1 count=20M
for read commands
sgp_dd if=/dev/sg1 of=/dev/null bs=512 bpt=<from 2-512> thr=8 time=1 count=20M

And the results are (all in MB/s):
bpt:		2	4	8	16	32	64	128	256	512
Write		22.5	41.4	80.6	160	275	443	570	740	810
Read		42	80	170	313	550	940	1200	1312	1300


What can be the reason for such difference between the bandwidth of Read and Write commands?

Thanks,
Doron