Re: [Scst-devel] ISCSI-SCST performance (with also IET and STGT data)

Bart Van Assche
2009-04-04T08:04:52Z

On Thu, Apr 2, 2009 at 7:16 PM, Vladislav Bolkhovitin <vst@vlnb.net> wrote:
> Bart Van Assche, on 04/02/2009 12:14 AM wrote:
>> I have repeated some of these performance tests for iSCSI over IPoIB
>> (two DDR PCIe 1.0 ConnectX HCA's connected back to back). The results
>> for the buffered I/O test with a block size of 512K (initiator)
>> against a file of 1GB residing on a tmpfs filesystem on the target are
>> as follows:
>>
>> write-test: iSCSI-SCST 243 MB/s; IET 192 MB/s.
>> read-test: iSCSI-SCST 291 MB/s; IET 223 MB/s.
>>
>> And for a block size of 4 KB:
>>
>> write-test: iSCSI-SCST 43 MB/s; IET 42 MB/s.
>> read-test: iSCSI-SCST 288 MB/s; IET 221 MB/s.
>
> Do you have any thoughts why writes are so bad? It shouldn't be so..

By this time I have run the following variation of the 4 KB write test:
* Target: iSCSI-SCST was exporting a 1 GB file residing on a tmpfs filesystem.
* Initiator: two processes were writing 4 KB blocks as follows:
dd if=/dev/zero of=/dev/sdb bs=4K seek=0 count=131072 oflag=sync &
dd if=/dev/zero of=/dev/sdb bs=4K seek=131072 count=131072 oflag=sync &

Results:
* Each dd process on the initiator was writing at a speed of 37.8
MB/s, or a combined writing speed of 75.6 MB/s.
* CPU load on the initiator system during the test: 2.0.
* According to /proc/interrupts, about 38000 mlx4-comp-0 interrupts
were triggered per second.

These results confirm that the initiator system was the bottleneck
during the 4 KB write test, not the target system.

Bart.