netdev - SMC-R problem under multithread

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Date:   Mon, 30 May 2022 11:16:04 +0800
From:   liuyacan@...p.netease.com
To:     kgraul@...ux.ibm.com, davem@...emloft.net, edumazet@...gle.com,
        kuba@...nel.org, pabeni@...hat.com
Cc:     linux-s390@...r.kernel.org, netdev@...r.kernel.org,
        linux-kernel@...r.kernel.org, ubraun@...ux.ibm.com,
        tonylu@...ux.alibaba.com
Subject: SMC-R problem under multithread

Hi experts,

  I recently used memcached to test the performance of SMC-R relative to TCP, but the results 
  are confusing me. When using multithread on the server side, the performance of SMC-R is not as good as TCP.

  Specifically, I tested 4 scenarios with server thread: 1\2\4\8. The client uses 8threads fixedly. 

  server: (smc_run) memcached -t 1 -m 16384 -p [SERVER-PORT] -U 0 -F -c 10240 -o modern
  client: (smc-run) memtier_benchmark -s [SERVER-IP] -p [SERVER-PORT] -P memcache_text --random-data --data-size=100 --data-size-pattern=S --key-minimum=30 --key-maximum=100  -n 5000000 -t 8

  The result is as follows:

  SMC-R:

  server-thread    ops/sec  client-cpu server-cpu
      1             242k        220%         97%
      2             362k        241%        128%
      4             378k        242%        160%
      8             395k        242%        210%

  TCP:
  server-thread    ops/sec  client-cpu server-cpu
      1             185k       224%         100%
      2             435k       479%         200%
      4             780k       731%         400%
      8             938k       800%         659%                   

  It can be seen that as the number of threads increases, the performance increase of SMC-R is much slower than that of TCP.

  Am I doing something wrong? Or is it only when CPU resources are tight that SMC-R has a significant advantage ?  

  Any suggestions are welcome.

Thanks & Regards,
Yacan.