Stupid idea for Mike: Would it make sense to add two special "commands" to iSCSI?:
1) Measure the No_ops per second (i.e. send as many No-Ops as possible (to test the TCP channel) 2) Measure the TUR (Test Unit Ready) (send as many TUR commands to test the end-to-end speed) I think that would put about the same load (bandwidth) on the transmit and receive channels. Then one could measure how a real data transfer in either direction affects those numbers. Apologies, if that's already possible. Regards, Ulrich >>> Vladislav Bolkhovitin <[email protected]> schrieb am 02.09.2011 um 05:04 in Nachricht <[email protected]>: > Hi, > > I've done some tests and looks like open-iscsi doesn't support full duplex > speed > on bidirectional data transfers from a single drive. > > My test is simple: 2 dd's doing big transfers in parallel over 1 GbE link > from a > ramdisk or nullio iSCSI device. One dd is reading and another one is > writing. I'm > watching throughput using vmstat. When any of the dd's working alone, I have > full > single direction link utilization (~120 MB/s) in both directions, but when > both > transfers working in parallel, throughput on any of them immediately drops > in 2 > times to 55-60 MB/s (sum is the same 120 MB/s). > > For sure, I tested bidirectional possibility of a single TCP connection and > it > does provide near 2 times throughput increase (~200 MB/s). > > Interesting, that doing another direction transfer from the same device > imported > from another iSCSI target provides expected full duplex 2x aggregate > throughput > increase. > > I tried several iSCSI targets + I'm pretty confident that iSCSI-SCST is > capable to > provide full duplex transfers, but from some look on the open-iscsi code I > can't > see the serialization point in it. Looks like open-iscsi receives and sends > data > in different threads (the requester process and per connection iscsi_q_X > workqueue > correspondingly), so should be capable to have full duplex. > > Does anyone have idea what could be the serialization point preventing full > duplex > speed? > > Thanks, > Vlad -- You received this message because you are subscribed to the Google Groups "open-iscsi" group. To post to this group, send email to [email protected]. To unsubscribe from this group, send email to [email protected]. For more options, visit this group at http://groups.google.com/group/open-iscsi?hl=en.
