Add a compile-stage2-under-perf step to "make perf" target.

mk/perf.mk

@@ -1 +1,12 @@
-perf: check-stage2-perf
+
+ifdef CFG_PERF_TOOL
+rustc-perf$(X): stage2/rustc$(X)
+	@$(call E, perf compile: $@)
+	$(PERF_STAGE1) -L stage2 -o $@ $(COMPILER_CRATE)
+	rm -f $@
+else
+rustc-perf$(X): stage2/rustc$(X)
+	touch $@
+endif
+
+perf: check-stage2-perf rustc-perf$(X)

mk/platform.mk

@@ -54,7 +54,7 @@ ifeq ($(CFG_OSTYPE), Linux)
 	  -e sched:sched_switch \
 	  -e fs:do_sys_open \
 	  -i \
-	  -r 10
+	  -r 3
   else
     ifdef CFG_VALGRIND
       CFG_PERF_TOOL :=\

mk/stageN.mk

@@ -46,6 +46,10 @@ STAGE$(2) := $$(Q)$$(call CFG_RUN_TARG,stage$(2), \
                 $$(CFG_VALGRIND_COMPILE) stage$(2)/rustc$$(X) \
                 $$(CFG_RUSTC_FLAGS))
 
+PERF_STAGE$(2) := $$(Q)$$(call CFG_RUN_TARG,stage$(2), \
+                $$(CFG_PERF_TOOL) stage$(2)/rustc$$(X) \
+                $$(CFG_RUSTC_FLAGS))
+
 stage$(2)/%.o: stage$(2)/%.s
 	@$$(call E, assemble [gcc]: $$@)
 	$$(Q)gcc $$(CFG_GCCISH_CFLAGS) -o $$@ -c $$<