Patch for configurable ERTS_DE_BUSY_LIMIT

[Rickard Green]

It seems reasonable to add a configuration parameter for this.

However:

We don't add new configuration parameters using environment variables. 
All new configuration parameters should be possible to pass as command 
line arguments.

Documentation of the parameter and a test case are needed.

You also need to submit the patch via git 
<http://wiki.github.com/erlang/otp/submitting-patches>.

Regards,
Rickard Green, Erlang/OTP, Ericsson AB.


Scott Lystig Fritchie wrote:
> Hi, all.  I sent a longer post to the erlang-questions about this.
> 
> In a busy system sending large messages in quick succession, I see
> 'busy_dist_port' messages coming to my monitoring proc, sometimes 5 or
> even 15 times per second for the same process.  And then there are the
> times where multiple processes are blocked due all sending to procs on
> the same destination node.
> 
> Don't get me wrong, this kind of scheduler-controlled congestion
> mechanism is a good thing.  But the 128KB limit feels cramped.  When
> using 4MB instead, in a system with modern 64-bit multi-core CPUs and
> gigabit Ethernet, the latency jitter appears to drop significantly for
> us.
> 
> Patch relative to R13B03.
> 
> -Scott
> 
> --- snip --- snip --- snip --- snip --- snip --- snip ---
> 
> diff -ur otp_src_R13B03.orig/erts/emulator/beam/dist.c otp_src_R13B03/erts/emulator/beam/dist.c
> --- otp_src_R13B03.orig/erts/emulator/beam/dist.c	2009-11-20 05:29:24.000000000 -0800
> +++ otp_src_R13B03/erts/emulator/beam/dist.c	2010-02-14 15:06:32.000000000 -0800
> @@ -97,6 +97,9 @@
>  #define PASS_THROUGH 'p'        /* This code should go */
>  
>  int erts_is_alive; /* System must be blocked on change */
> +#define ERTS_DE_BUSY_LIMIT (128*1024)
> +int erts_de_busy_limit =RTS_DE_BUSY_LIMIT;
> +
>  
>  /* distribution trap functions */
>  Export* dsend2_trap =ULL;
> @@ -1407,8 +1410,6 @@
>      return -1;
>  }
>  
> -#define ERTS_DE_BUSY_LIMIT (128*1024)
> -
>  static int
>  dsig_send(ErtsDSigData *dsdp, Eterm ctl, Eterm msg, int force_busy)
>  {
> diff -ur otp_src_R13B03.orig/erts/emulator/beam/erl_init.c otp_src_R13B03/erts/emulator/beam/erl_init.c
> --- otp_src_R13B03.orig/erts/emulator/beam/erl_init.c	2009-09-18 07:07:46.000000000 -0700
> +++ otp_src_R13B03/erts/emulator/beam/erl_init.c	2010-02-14 16:08:33.000000000 -0800
> @@ -788,6 +788,7 @@
>      char envbuf[21]; /* enough for any 64-bit integer */
>      size_t envbufsz;
>      int async_max_threads =rts_async_max_threads;
> +    extern int erts_de_busy_limit;
>  
>      early_init(&argc, argv);
>  
> @@ -807,6 +808,9 @@
>      if (erts_sys_getenv("ERL_THREAD_POOL_SIZE", envbuf, &envbufsz) =0) {
>  	async_max_threads =toi(envbuf);
>      }
> +    if (erts_sys_getenv("ERTS_DE_BUSY_LIMIT", envbuf, &envbufsz) =0) {
> +	erts_de_busy_limit =toi(envbuf);
> +    } 
>      
>  
>  #ifdef DEBUG
>