Erez Zilber wrote:
> open-iscsi sends nop-outs to the target. If the target responds quick
> enough, we don't get a timeout. I'd like to know (for internal debug
> purposes) how many times the ping timer almost expired. This sounds
> like a useful feature also for other open-iscsi developers/users.
> 
> I was thinking about adding the following mechanism:
> 
> 1. Add an array of some length to store long nop-outs. Protect it with
> some lock.
> 2. If a nop-in (as a response to nop-out) was received after >= 0.7 *
> ping_to (or 0.8 or whatever), add some info about it to the array
> (when was the nop-out sent, how much time until we got a nop-in etc).
> 3. The array should be used in a cyclic way - when it gets full,
> overwrite the 1st entry.
> 4. We can dump the info from the array from time to time or the user
> may use iscsiadm to do that. When this is done, we can delete the
> contents of the array.
> 

What info did you want to store?


What about some perf counters for it? Add a counter for if a ping took 
a-b secs, b-c secs, and c-d secs. Userspace could then just get that 
info with the other stats. Also maybe a new iscsi_connection sysfs entry 
that exports the avg time to complete a nop might be nice. It might help 
people config the value.

You also probably want to add something to reset the counters too.

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