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  1. Kudu
  2. KUDU-2758

TLS socket writes in 16kb chunks with intervening epoll/setsockopt syscalls

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    Details

    • Type: Bug
    • Status: Open
    • Priority: Major
    • Resolution: Unresolved
    • Affects Version/s: None
    • Fix Version/s: None
    • Component/s: perf, rpc, security
    • Labels:
      None

      Description

      I noticed that krpc has the following syscall pattern:

       rpc reactor-231 23122 [002] 35488410.994309: syscalls:sys_enter_epoll_wait: epfd: 0x00000007, events: 0x02137520, maxevents: 0x00000040, timeout: 0x00000050
       rpc reactor-231 23122 [002] 35488410.994310: syscalls:sys_exit_epoll_wait: 0x1
       rpc reactor-231 23122 [002] 35488410.994313: syscalls:sys_enter_setsockopt: fd: 0x00000011, level: 0x00000006, optname: 0x00000003, optval: 0x7fc80910175c, optlen: 0x00000004
       rpc reactor-231 23122 [002] 35488410.994314: syscalls:sys_exit_setsockopt: 0x0
       rpc reactor-231 23122 [002] 35488410.994351: syscalls:sys_enter_write: fd: 0x00000011, buf: 0x7fc7e8059e93, count: 0x0000401d
       rpc reactor-231 23122 [002] 35488410.994370: syscalls:sys_exit_write: 0x401d
       rpc reactor-231 23122 [002] 35488410.994372: syscalls:sys_enter_setsockopt: fd: 0x00000011, level: 0x00000006, optname: 0x00000003, optval: 0x7fc80910175c, optlen: 0x00000004
       rpc reactor-231 23122 [002] 35488410.994378: syscalls:sys_exit_setsockopt: 0x0
      

      This block of syscalls repeats in a pretty tight loop – epoll_wait, CORK, write, UNCORK. The writes are always 0x401d bytes (just more than 16kb). I found the following in the ssl_write manpage:

      SSL_write() will only return with success, when the complete contents of buf of length num has been written. This default behaviour can be changed with the SSL_MODE_ENABLE_PARTIAL_WRITE option of ssl_ctx_set_mode(3). When this flag is set, SSL_write() will also return with success, when a partial write has been successfully completed. In this case the SSL_write() operation is considered completed. The bytes are sent and a new SSL_write() operation with a new buffer (with the already sent bytes removed) must be started. A partial write is performed with the size of a message block, which is 16kB for SSLv3/TLSv1.

      Seems likely we should be looping the writes before uncorking – either until we run into a temporary socket error or run out of stuff to write.

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            • Assignee:
              Unassigned
              Reporter:
              tlipcon Todd Lipcon
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              • Created:
                Updated: