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

[Vladislav Bolkhovitin]

Tomasz Chmielewski wrote:
> 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).

Tomasz meant here that on his target both network and backstorage 
hardware sit on the same 32-bit 33MHz PCI and share its bandwidth, which 
is less, than 100MB/s. I.e. he can at max get ~40MB/s (since his array 
has 70MB/s) + sharing overhead.

> 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?
> 
> 
>