pack: set manual lazy value

src/app/fdctl/run/run1.c

@@ -149,6 +149,9 @@ tile_main( void * _args ) {
   void * ctx = NULL;
   if( FD_LIKELY( config->mux_ctx ) ) ctx = config->mux_ctx( scratch_mem );
 
+  long lazy = 0L;
+  if( FD_UNLIKELY( config->lazy ) ) lazy = config->lazy( scratch_mem );
+
   fd_rng_t rng[1];
   fd_mux_tile( tile->cnc,
                config->mux_flags,
@@ -160,7 +163,7 @@ tile_main( void * _args ) {
                out_fseq,
                config->burst,
                0,
-               0,
+               lazy,
                fd_rng_join( fd_rng_new( rng, 0, 0UL ) ),
                fd_alloca( FD_MUX_TILE_SCRATCH_ALIGN, FD_MUX_TILE_SCRATCH_FOOTPRINT( tile->in_cnt, out_cnt_reliable ) ),
                ctx,

src/app/fdctl/run/tiles/fd_pack.c

@@ -480,6 +480,21 @@ unprivileged_init( fd_topo_t *      topo,
     FD_LOG_ERR(( "scratch overflow %lu %lu %lu", scratch_top - (ulong)scratch - scratch_footprint( tile ), scratch_top, (ulong)scratch + scratch_footprint( tile ) ));
 }
 
+static long
+lazy( fd_topo_tile_t * tile ) {
+  (void)tile;
+  /* We want lazy (measured in ns) to be small enough that the producer
+     and the consumer never have to wait for credits.  For most tango
+     links, we use a default worst case speed coming from 100 Gbps
+     Ethernet.  That's not very suitable for microblocks that go from
+     pack to bank.  Instead we manually estimate the very aggressive
+     1000ns per microblock, and then reduce it further (in line with the
+     default lazy value computation) to ensure the random value chosen
+     based on this won't lead to credit return stalls. */
+  return 128L * 300L;
+}
+
+
 static ulong
 populate_allowed_seccomp( void *               scratch,
                           ulong                out_cnt,
@@ -512,6 +527,7 @@ fd_tile_config_t fd_tile_pack = {
   .mux_after_credit         = after_credit,
   .mux_during_frag          = during_frag,
   .mux_after_frag           = after_frag,
+  .lazy                     = lazy,
   .populate_allowed_seccomp = populate_allowed_seccomp,
   .populate_allowed_fds     = populate_allowed_fds,
   .scratch_align            = scratch_align,

src/app/fdctl/run/tiles/tiles.h

@@ -21,6 +21,7 @@ typedef struct {
   fd_mux_after_frag_fn          * mux_after_frag;
   fd_mux_metrics_write_fn       * mux_metrics_write;
 
+  long  (*lazy                    )( fd_topo_tile_t * tile );
   ulong (*populate_allowed_seccomp)( void * scratch, ulong out_cnt, struct sock_filter * out );
   ulong (*populate_allowed_fds    )( void * scratch, ulong out_fds_sz, int * out_fds );
   ulong (*loose_footprint         )( fd_topo_tile_t * tile );