Pasi Kärkkäinen, on 08/24/2010 11:25 AM wrote:
On Mon, Aug 23, 2010 at 02:03:26PM -0400, Chetan Loke wrote:
I actually received 3+ off-post emails asking whether I was talking
about initiator or target in the 100K IOPS case below and what did I
mean by the ACKs.
I was referring to the 'Initiator' side.
ACKs == When scsi-ML down-calls the LLD via the queue-command, process
the sgl's(if you like) and then trigger the scsi_done up-call path.
Uhm, Intel and Microsoft demonstrated over 1 million IOPS
using software iSCSI and a single 10 Gbit Ethernet NIC (Intel 82599).
How come there is such a huge difference? What are we lacking in Linux?
I also have an impression that Linux I/O subsystem has some performance
problems. For instance, in one recent SCST performance test only 8 Linux
initiators with fio as a load generator were able to saturate a single
SCST target with dual IB cards (SRP) on 4K AIO direct accesses over an
SSD backend. This rawly means that any initiator took several times (8?)
more processing time than the target. Hardware used for that target and
initiators was the same. I can't see on this load why the initiators
would need to do something more than the target. Well, I know we in SCST
did an excellent work to maximize performance, but such a difference
looks too much ;)
Also it looks very suspicious why nobody even tried to match that
Microsoft/Intel record, even Intel itself who closely works with Linux
community in the storage area and could do it using the same hardware.
Vlad
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