Re: [libmicrohttpd] Require info on setting TCP_NODELAY for MHD

[Badari Prasad]

Hi Christian, 

 My application runs on fedora and is single threaded, for my testing application just receives the request and responds with 200OK with some json body (size <100 bytes )in the response.

I did try running strace on MHD  this is what I got. (client I am using libcurl application which sends 33k of body in http post with out Expect 100 header) 

14:38:14.623432 epoll_wait(12, [{EPOLLIN|EPOLLOUT, {u32=21908544, u64=21908544}}], 128, 0) = 1

14:38:14.623509 recvfrom(13, "POST /hello/TestMsg/async"..., 16384, 0, NULL, NULL) = 16384

14:38:14.623825 rt_sigprocmask(SIG_UNBLOCK, [HUP QUIT PIPE ALRM TERM CHLD CONT TSTP TTIN TTOU WINCH IO PWR], NULL, 8) = 0

14:38:14.623880 epoll_wait(5, [], 2, 50) = 0

14:38:14.674038 rt_sigprocmask(SIG_BLOCK, [HUP QUIT PIPE ALRM TERM CHLD CONT TSTP TTIN TTOU WINCH IO PWR], NULL, 8) = 0

14:38:14.674135 epoll_wait(12, [], 128, 0) = 0

14:38:14.674175 recvfrom(13, "ey\": \"4\"\n},{\n    \"key\": \"0\",\n   "..., 15919, 0, NULL, NULL) = 15919

14:38:14.674329 rt_sigprocmask(SIG_UNBLOCK, [HUP QUIT PIPE ALRM TERM CHLD CONT TSTP TTIN TTOU WINCH IO PWR], NULL, 8) = 0

14:38:14.674375 epoll_wait(5, [], 2, 50) = 0

14:38:14.724568 rt_sigprocmask(SIG_BLOCK, [HUP QUIT PIPE ALRM TERM CHLD CONT TSTP TTIN TTOU WINCH IO PWR], NULL, 8) = 0

14:38:14.724666 epoll_wait(12, [], 128, 0) = 0

14:38:14.724715 recvfrom(13, "key\": \"3\",\n    \"key\": \"4\"\n},{\n  "..., 15919, 0, NULL, NULL) = 1878

....

....

14:38:14.743832 setsockopt(13, SOL_TCP, TCP_NODELAY, [0], 4) = 0

14:38:14.743908 setsockopt(13, SOL_TCP, TCP_CORK, [1], 4) = 0

14:38:14.743949 sendto(13, "HTTP/1.1 200 OK\r\nConnection: Kee"..., 162, MSG_NOSIGNAL, NULL, 0) = 162

14:38:14.744022 setsockopt(13, SOL_TCP, TCP_CORK, [0], 4) = 0

14:38:14.744189 setsockopt(13, SOL_TCP, TCP_NODELAY, [1], 4) = 0

14:38:14.744234 setsockopt(13, SOL_TCP, TCP_NODELAY, [0], 4) = 0

14:38:14.744286 setsockopt(13, SOL_TCP, TCP_CORK, [1], 4) = 0    

Time diff I see is about 120 milli secs between MHD receiving request and sending response to the client.

With this I got to understand that TCP_CORK and TCP_NODELAY is kind off delaying the response being sent out on transport layer... 

Is their a way to always enable TCP_NODELAY on MHD ? and check if we see this delay on transport layer ?

Thanks in advance,

 Badari 

On Sat, Nov 10, 2018 at 11:53 PM Christian Grothoff <address@hidden> wrote:

On 11/9/18 5:44 PM, Badari Prasad wrote:
> Hi,
>   I was going through old mailist archives, found one thread on
> TCP_NODELAY
> : https://lists.gnu.org/archive/html/libmicrohttpd/2015-11/msg00077.html
> But couldn't know if the option provided is it at compile time flag or
> runtime flag per connection basis.
>
> Kindly let me know the information on TCP_NODELAY option at MHD.

Hi!

To the best of my knowledge (i.e. unless there is a bug), TCP_NODELAY
should be set/unset by MHD automatically whenever it makes sense to do
so. Your application doesn't need to do anything here.

If you find/suspect that corking is inappropriately used, please send a
packet trace and maybe a bit of explanation as to how your code works
(in particular, which platform you use and which threading mode is in use).

Happy hacking!

Christian