[jira] [Commented] (KUDU-2758) TLS socket writes in 16kb chunks with intervening epoll/setsockopt syscalls

["Todd Lipcon (JIRA)" <ji...@apache.org>]

    [ https://issues.apache.org/jira/browse/KUDU-2758?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16808235#comment-16808235 ] 

Todd Lipcon commented on KUDU-2758:
-----------------------------------

[~kwho] you might be interested in this for Impala's usage of KRPC as well.

> TLS socket writes in 16kb chunks with intervening epoll/setsockopt syscalls
> ---------------------------------------------------------------------------
>
>                 Key: KUDU-2758
>                 URL: https://issues.apache.org/jira/browse/KUDU-2758
>             Project: Kudu
>          Issue Type: Bug
>          Components: perf, rpc, security
>            Reporter: Todd Lipcon
>            Priority: Major
>
> I noticed that krpc has the following syscall pattern:
> 
> {code}
>  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
> {code}
> 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:
> {quote}
> 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.
> {quote}
> 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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