On Wednesday, June 27, 2018 at 12:34:56 PM UTC-7, Neutron Sharc wrote:
> Hi all,
> I will describe the problem I saw step by step. Please take patience.
> I'm using tgt as iscsi target server (fujita/tgt from github) on Ubuntu 
> 16.04.  iscsi initiator runs the stock open-iscsi coming with Ubuntu 16.04.
> The default "/etc/iscsi/iscsid.conf" defines "node.session.queue_depth = 
> 32".  I changed it to 128, and run "sudo iscsid restart".  Then I log in to 
> an iscsi target.
> However, " iscsiadm -m node -p xxx  -T yyy" shows my iscsi session still 
> uses "queue_depth" as 32, not 128.
> Then I run  "iscsiadm -m node -p xxx -T yyy --op update -n 
> node.session.queue_depth  -v 128" to forcefully change the value. 
> This time "iscsiadm -m node" shows the correct "128" value I set.
> Now I run fio benchmark with a large queue size (1024),  and keeps 
> monitoring iscsi target.  I had a patch in tgt to report the current live 
> commands received on a connection.
> To my surprise, this max "queued_cmd" is always 32, not 128,  no matter 
> how hard I push fio queue size.
> I was expecting that,  since I set initiator  session.queue_depth to 128,  
> the target should receive a max 128 cmds in its queue. 
> I want the initiator to push as many requests as possible to target to get 
> more bandwidth.  However the target only receives up to 32 outstanding cmds 
> from initiator.  Why doesn't initiator push more?
> Is my understanding about "node.session.queue_depth" correct?
> -Shawn
> I _believe_ that queue_depth, in this context, ralates to the cmdsn 
(command sequence number) window that the iscsi transport will allow, i.e. 
how many iSCSI commands can be active at one time? But that's from a really 
quick glance at the code.

Also, as far as setting it in iscsid.conf, that doesn't effect any current 
node records. You can change the node "queue_depth" value using "iscsiadm 
-m node ... --name node.session.queue_depth --value SOME_NUMBER"

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