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Re: [dm-devel] Re: [PATCH] Add ALUA hardware handler

Hannes Reinecke wrote:
Mike Christie wrote:
Hannes Reinecke wrote:
Hi Alasdair,

this is a patch to add a SPC-3 hardware handler. SPC-3 ALUA has
provisioning for 'explicit' port group state change via the
SET TARGET GROUP STATES command, and some newer storage
arrays do benefit from this.
Eg HP EVAs and newer EMC Clariions already support explicit ALUA.

Please apply.



Does this also work for adaptec or snap iscsi targets or whatever they
are called targets?

Don't know, I don't have one. Care to try?

I do not have it. I was asking because some people were asking about alua and I told them to talk to you.

Just some quick higher level comments

+static int submit_std_inquiry(struct alua_handler *h)
+    struct request *rq;
+    unsigned err = (DRIVER_ERROR << 24);
+    rq = prepare_req(h, h->inq, TPGS_INQUIRY_SIZE, READ);

I do not think you want to use GFP_KERNEL allocations in this path, so
all the prepare_req allocs should be changed. GFP_NOIO is probably best.

Yes, probably.

+    if (!rq)
+        return err;
+    /* Prepare the command. */
+    rq->cmd[0] = INQUIRY;
+    rq->cmd[1] = 0;
+    rq->cmd[2] = 0;
+    rq->cmd[4] = TPGS_INQUIRY_SIZE;
+    rq->cmd_len = COMMAND_SIZE(INQUIRY);
+    blk_execute_rq(rq->q, NULL, rq, 1);

There is only one workqueue for all the dm devices, so you do not want
to do one command (or how many processors there are) at a time and wait
for each one to complete with blk_execute_rq. You should use the async
one, blk_execute_rq_nowait, like rdac.

This is actually by design. Problem here is the port group as returned by
REPORT TARGET PORT GROUPS does not have any association to the controller
which handles these ports.
So if we were to send all REPORT TARGET PORT GROUPS commands (roughly)
simultaneously we're pretty much guaranteed to hit the same controller
several times; and if we have to do a SET TARGET PORT GROUPS in addition
we'll be having to do loads of retries as the controller might be busy
(if he's transitioning) or reporting an UNIT ATTENTION if the port
group states have been updated. So I'd rather keep it that way so as
to not flood the controller. And then we're only having to send two
commands, so this should okay even sequentially.

What if I have emc box and another non alua box? Your handler blocks activity for all other devices.

And incidentally, rdac implements it's own workqueue per controller

rdac does one single threaded workqueue for the entire module, and it does not send IO synchronously.

as it's only capable to handle one MODE SELECT command at time.

Yeah, and chandra handled it in a way that does not affect all other handlers.

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