Add STARPU_TRACE_BUFFER_SIZE environment variable to easily set the FxT buffer size

doc/doxygen/chapters/40environment_variables.doxy

@@ -548,6 +548,15 @@ intended to be used for experimental purposes as it emulates devices
 that have a limited amount of memory.
 </dd>
 
+<dt>STARPU_TRACE_BUFFER_SIZE</dt>
+<dd>
+\anchor STARPU_TRACE_BUFFER_SIZE
+\addindex __env__STARPU_TRACE_BUFFER_SIZE
+This sets the buffer size for recording trace events in MiB. Setting it to a big
+size allows to avoid pauses in the trace while it is recorded on the disk. This
+however also consumes memory, of course. The default value is 64.
+</dd>
+
 <dt>STARPU_GENERATE_TRACE</dt>
 <dd>
 \anchor STARPU_GENERATE_TRACE

src/core/workers.c

@@ -863,7 +863,7 @@ int starpu_conf_init(struct starpu_conf *conf)
 #endif
 
 	/* 64MiB by default */
-	conf->trace_buffer_size = 64<<20;
+	conf->trace_buffer_size = starpu_get_env_number_default("STARPU_TRACE_BUFFER_SIZE", 64) << 20;
 	return 0;
 }