On Mon, Sep 27, 2021 at 03:09:44PM +0300, Leon Romanovsky wrote:

On Sun, Sep 26, 2021 at 05:36:01PM +0000, Chuck Lever III wrote:

quoted

Hi Leon-

Thanks for the suggestion! More below.

quoted

On Sep 26, 2021, at 4:02 AM, Leon Romanovsky [off-list ref] wrote:

On Fri, Sep 24, 2021 at 03:34:32PM +0000, bugzilla-daemon@bugzilla.kernel.org wrote:

quoted

https://bugzilla.kernel.org/show_bug.cgi?id=214523

           Bug ID: 214523
          Summary: RDMA Mellanox RoCE drivers are unresponsive to ARP
                   updates during a reconnect
          Product: Drivers
          Version: 2.5
   Kernel Version: 5.14
         Hardware: All
               OS: Linux
             Tree: Mainline
           Status: NEW
         Severity: normal
         Priority: P1
        Component: Infiniband/RDMA
         Assignee: drivers_infiniband-rdma@kernel-bugs.osdl.org
         Reporter: kolga@netapp.com
       Regression: No

RoCE RDMA connection uses CMA protocol to establish an RDMA connection. During
the setup the code uses hard coded timeout/retry values. These values are used
for when Connect Request is not being answered to to re-try the request. During
the re-try attempts the ARP updates of the destination server are ignored.
Current timeout values lead to 4+minutes long attempt at connecting to a server
that no longer owns the IP since the ARP update happens. 

The ask is to make the timeout/retry values configurable via procfs or sysfs.
This will allow for environments that use RoCE to reduce the timeouts to a more
reasonable values and be able to react to the ARP updates faster. Other CMA
users (eg IB or others) can continue to use existing values.

I would rather not add a user-facing tunable. The fabric should
be better at detecting addressing changes within a reasonable
time. It would be helpful to provide a history of why the ARP
timeout is so lax -- do certain ULPs rely on it being long?

I don't know about ULPs and ARPs, but how to calculate TimeWait is
described in the spec.

Regarding tunable, I agree. Because it needs to be per-connection, most
likely not many people in the world will success to configure it properly.

Maybe we should be disconnecting the cm_id if a gratituous ARP changes
the MAC address? The cm_id is surely broken after that event right?

Jason