On Sun, Sep 26, 2021 at 05:36:01PM +0000, Chuck Lever III wrote: > Hi Leon- > > Thanks for the suggestion! More below. > > > On Sep 26, 2021, at 4:02 AM, Leon Romanovsky <leon@xxxxxxxxxx> wrote: > > > > On Fri, Sep 24, 2021 at 03:34:32PM +0000, bugzilla-daemon@xxxxxxxxxxxxxxxxxxx wrote: > >> 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@xxxxxxxxxxxxxxxxxxxx > >> Reporter: kolga@xxxxxxxxxx > >> 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. > > > >> The problem exist in all kernel versions but bugzilla is filed for 5.14 kernel. > >> > >> The use case is (RoCE-based) NFSoRDMA where a server went down and another > >> server was brought up in its place. RDMA layer introduces 4+ minutes in being > >> able to re-establish an RDMA connection and let IO resume, due to inability to > >> react to the ARP update. > > > > RDMA-CM has many different timeouts, so I hope that my answer is for the > > right timeout. > > > > We probably need to extend rdma_connect() to receive remote_cm_response_timeout > > value, so NFSoRDMA will set it to whatever value its appropriate. > > > > The timewait will be calculated based it in ib_send_cm_req(). > > I hope a mechanism can be found that behaves the same or nearly the > same way for all RDMA fabrics. It depends on the fabric itself, in every network remote_cm_response_timeout can be different. > > For those who are not NFS-savvy: > > Simple NFS server failover is typically implemented with a heartbeat > between two similar platforms that both access the same backend > storage. When one platform fails, the other detects it and takes over > the failing platform's IP address. Clients detect connection loss > with the failing platform, and upon reconnection to that IP address > are transparently directed to the other platform. > > NFS server vendors have tried to extend this behavior to RDMA fabrics, > with varying degrees of success. > > In addition to enforcing availability SLAs, the time it takes to > re-establish a working connection is critical for NFSv4 because each > client maintains a lease to prevent the server from purging open and > lock state. If the reconnect takes too long, the client's lease is > jeopardized because other clients can then access files that client > might still have locked or open. > > > -- > Chuck Lever > > >
