On Thu, Apr 2, 2009 at 7:16 PM, Vladislav Bolkhovitin <vst@xxxxxxxx> wrote:Bart Van Assche, on 04/02/2009 12:14 AM wrote:I have repeated some of these performance tests for iSCSI over IPoIBDo you have any thoughts why writes are so bad? It shouldn't be so..
(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.
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.
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