On 05/09/25 5:31 pm, Halil Pasic wrote: > On Fri, 5 Sep 2025 11:00:59 +0200 > Halil Pasic <pasic@xxxxxxxxxxxxx> wrote: > >>> 1. What if the two sides have different max_send_wr/max_recv_wr configurations? >>> IIUC, For example, if the client sets max_send_wr to 64, but the server sets >>> max_recv_wr to 16, the client might overflow the server's QP receive >>> queue, potentially causing an RNR (Receiver Not Ready) error. >> >> I don't think the 16 is spec-ed anywhere and if the client and the server >> need to agree on the same value it should either be speced, or a >> protocol mechanism for negotiating it needs to exist. So what is your >> take on this as an SMC maintainer? >> >> I think, we have tested heterogeneous setups and didn't see any grave >> issues. But let me please do a follow up on this. Maybe the other >> maintainers can chime in as well. > > Did some research and some thinking. Are you concerned about a > performance regression for e.g. 64 -> 16 compared to 16 -> 16? According > to my current understanding the RNR must not lead to a catastrophic > failure, but the RDMA/IB stack is supposed to handle that. > Hi Dust, I configured a client-server setup & did some SMC-R testing by setting the values you proposed. Ran iperf3(using smc_run) with max parallel connections of 128 & it looks good. No tcp fallback. No obvious errors. As Halil mentioned I don't see any catastrophic failure here. Let me know if I need to stress the system by some more tests or any specific test that you can think may cause RNR errors. The setup is ready & I can try it. *Client* side logs: [root@client ~]$ sysctl net.smc.smcr_max_send_wr net.smc.smcr_max_send_wr = 64 [root@client ~]$ [root@client ~]$ smc_run iperf3 -P 128 -t 120 -c 10.25.0.72 Connecting to host 10.25.0.72, port 5201 [ 5] local 10.25.0.73 port 52544 connected to 10.25.0.72 port 5201 [ 7] local 10.25.0.73 port 52558 connected to 10.25.0.72 port 5201 *Server* side logs: [root@server ~]$ sysctl net.smc.smcr_max_recv_wr net.smc.smcr_max_recv_wr = 16 [root@client ~]$ [root@server~]$ smc_run iperf3 -s ----------------------------------------------------------- Server listening on 5201 (test #1) -----------------------------------------------------------
