Erez Zilber wrote:
>> Erez Zilber wrote:
>>> Mike,
>>> I'm still investigating the performance problems in open-iscsi over iSER, 
>>> and I think that I see the cause of the problem:
>>> I've added an outstanding commands counter. It's incremented when 
>>> iscsi_queuecommand is called and decremented when iscsi_complete_command is 
>>> called. After decrementing the counter, I save it's value in some global 
>>> array. I print this array when iscsi_session_teardown is called.
>> >From what I see, in ~25% of command completions, the command queue is empty 
>> >(i.e. outstanding_cmds = 0). This can explain the low throughput that I see 
>> >with iSER.
>>> What could be the cause for that? Is there anything not well configured in 
>>> the scsi_host_template that we use? Anything else?
>> I saw this when using all io schedulers except noop. When I set the
>> queue to use noop, The iscsi queue was full (host_busy was greater than
>> 1) most of the time and thoughout was higher. I was going by just checking
>> /sys/class/scsi_host/hostX/host_busy
> I'm not familiar with "io schdulers". What's that? You're not talking about 
> benchmraks, right?

No. Sorry, I misspelled it :) io schedulers - maybe you call them 
elevators or something else. The kernel code that determines when to

(write to this to switch schedulers and read it see the ones available)
(dir with lots of settings)

Here is some basic info

There is some more info with the kernel source here: Documentation/block

And then there is the code in the kernel source block dir.

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