[Stgt-devel] some simple tgt / iSCSI-SCST performance tests

[Tomasz Chmielewski]

I made some simple performance tests of tgt and iSCSI-SCST.


Reading the array on a target machine to /dev/null gives me ~70 MB/s.

When I read the same array on the initiator with tgt as a target, it 
gives me ~25 MB/s.

With iSCSI-SCST, I get ~35 MB/s (although I think I maxed out the PCI at 
this point; on something more modern it could be better).

I dropped caches before each test.


Also, CPU load is slightly bigger when tgtd is used as a target, 
although I didn't do any precise measurements here. With tgt, both CPU 
usage was more or less settled at the same level; with SCST CPU0 usage 
jumped up and down by +/- 20%; CPU1 usage for SCST was more or less at 
the same level.
It would be nice to know more on the nature of these CPU usage spikes 
for SCST (and possibly, how it could affect i.e. reading from an 
encrypted device-mapper volume).


tgt-git:
CPU0: ~30%
CPU1: ~90%

SCST-r234:
CPU0: ~30%
CPU1: ~80%



Read on the target:

# dd if=/dev/sda of=/dev/null bs=64k count=50000
50000+0 records in
50000+0 records out
3276800000 bytes (3.3 GB) copied, 45.9789 seconds, 71.3 MB/s



SCST-r234:

# dd if=/dev/sdba of=/dev/null bs=64k count=50000
50000+0 records in
50000+0 records out
3276800000 bytes (3.3 GB) copied, 90.817 seconds, 36.1 MB/s



tgt-git:

# dd if=/dev/sday of=/dev/null bs=64k count=50000
50000+0 records in
50000+0 records out
3276800000 bytes (3.3 GB) copied, 140.123 seconds, 23.4 MB/s



tgt-20071014:

# dd if=/dev/sday of=/dev/null bs=64k count=50000
50000+0 records in
50000+0 records out
3276800000 bytes (3.3 GB) copied, 138.754 seconds, 23.6 MB/s





BTW, is it possible to do a nullio test with tgt target?



-- 
Tomasz Chmielewski
http://wpkg.org