On 09/01/2011 10:04 PM, Vladislav Bolkhovitin wrote: > 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.
Yeah, we send from the iscsi_q workqueue and receive from the network softirq if the net driver supports NAPI. > > Does anyone have idea what could be the serialization point preventing full > duplex > speed? > Did you do any lock profiliing and is the session->lock look the problem? It is taken in both the receive and xmit paths and also the queuecommand path. -- You received this message because you are subscribed to the Google Groups "open-iscsi" group. To post to this group, send email to open-iscsi@googlegroups.com. To unsubscribe from this group, send email to open-iscsi+unsubscr...@googlegroups.com. For more options, visit this group at http://groups.google.com/group/open-iscsi?hl=en.
