On 02/24/2010 09:49 AM, Or Gerlitz wrote:
Mike Christie wrote:
the noop-out based watch-dog serve all transports, correct?
Yes
okay
narrow down things and understand if/what is the transport role:
For the nop out path, the trasnport just has to send/recv the nop pdu/response
okay, fair-enough
They do not have to make those calls for multipath to work. Multipath
will work better if the transport can signal when there is a problem,
because we can stop using a bad path and get IO going to a working path
faster. If the transport does nothing then we have to rely on the scsi
error handler/timeout to detect the problem and that is very slow.
I am still confused, in somehow black box manner, I understand and see (...)
that:
A) the nop out based watch-dog serves all transports
B) if/when the transport doesn't signal to iscsi there's a problem with a
session
multipathing works much more slower.
combining A&& B I still don't see what is the exact role of the watch-dog,
anyway,
The nop watch dog is more of generic catch all problems. I think I was
saying offlist that iscsi_tcp is not able to detect many transport
problems quickly. For example if you just pulled a cable somewhere in
the network, iscsi_tcp may not get some event telling us this. If nops
are off, then we would have to wait for the scsi cmd timer to fire. To
speed this type of failure up, we do the nops.
If for iser you can figure out every transport problem with some sort of
event notification system then you could turn off nops.
maybe you should let me get some more millage on the thing and I'll get that...
You should also change your ep_disconnect because it is not
supposed to block (did we talk about this or was this just bnx2i), since
it will stop iscsid from processing other events.
no, I didn't realized ep_connect shouldn't block up till we brought it here.
Couples of years back when we did ep_connect/poll/disconnect we said that
ep_connect initiates the connection establishment process and ep_poll reports
about the progress. It turns out that I didn't pay attention to the price payed
when ep_disconnect blocks. Let me take a look if I can just change it
internally in iser or a patch to iscsi is needed, thanks for pointing this out!
Let me know if you need something like a ep_discocnnect_poll() where the
ep_disconnect() starts the disconnect, then then new ep_disconnect_poll
would wait for it to complete.
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