Scale invocation count by the number of BBs in the flow-graph of a method.

runtime/vm/flow_graph_compiler_ia32.cc

Index: runtime/vm/flow_graph_compiler_ia32.cc
diff --git a/runtime/vm/flow_graph_compiler_ia32.cc b/runtime/vm/flow_graph_compiler_ia32.cc
index a00e8b99efe1c8f7d2133a56aadf0abce5920843..afd779a069f112d6ed1cfeba0d5cef5deb45f344 100644
--- a/runtime/vm/flow_graph_compiler_ia32.cc
+++ b/runtime/vm/flow_graph_compiler_ia32.cc
@@ -29,6 +29,10 @@ DECLARE_FLAG(int, optimization_counter_threshold);
 DECLARE_FLAG(int, reoptimization_counter_threshold);
 DECLARE_FLAG(bool, enable_type_checks);
 DECLARE_FLAG(bool, enable_simd_inline);
+DEFINE_FLAG(int, optimization_counter_scale, 2270,

[Vyacheslav Egorov (Google), 2014/08/28 14:26:40]

Maybe use 100 * Math.pow(Math.PI, Math.E) here? :)

[Anders Johnsen, 2014/08/28 14:44:16]

I'm not sure - where do you get that "magic number 100" from??? :)

[srdjan, 2014/08/28 16:49:16]

The number is definitely wrong, it must be a typo and should be 2718.

[srdjan, 2014/08/28 17:39:10]

On a serious note: do specific number (2270) looks fragile? Do 2000 or 3000 make
a lot of difference? 

[Vyacheslav Egorov (Google), 2014/08/28 18:06:49]

I would like to clarify where 2270 came from: originally Anders suggested
quadratic scaling a*x^2 + b * x + c which did not make much sense to me --- so I
suggested to use 2270 instead which is the tangent of the line which intersects
lines x = 0 and y = 30000 in the same points as Anders'es parabola (essentially
it's a linear approximation of the same quadratic scaling which actually grows
faster on this interval).



On 2014/08/28 17:39:10, srdjan wrote:

[Anders Johnsen, 2014/08/29 07:11:37]

Yes, the quadratic scale came from Karl and I experimenting, but as Slava found,
the curve was very close to a line for our use-case range. I've found 2000 to
work just as well.

+            "The scale of invocation count, by size of the function.");
+DEFINE_FLAG(int, optimization_counter_start, 5000,
+            "The minimum invocation count for a function.");

[srdjan, 2014/08/28 17:39:10]

Maybe rename to min_optimization_counter_threshold?

[Anders Johnsen, 2014/08/29 07:11:37]

Done.

 
 
 FlowGraphCompiler::~FlowGraphCompiler() {
@@ -1000,9 +1004,16 @@ void FlowGraphCompiler::EmitFrameEntry() {
       __ cmpl(FieldAddress(function_reg, Function::usage_counter_offset()),
               Immediate(FLAG_reoptimization_counter_threshold));
     } else {
+      intptr_t basic_blocks = flow_graph().preorder().length();

[srdjan, 2014/08/28 17:39:10]

const

[Anders Johnsen, 2014/08/29 07:11:37]

Done.

+      ASSERT(basic_blocks > 0);
+      intptr_t limit = FLAG_optimization_counter_scale * basic_blocks +
+          FLAG_optimization_counter_start;

[srdjan, 2014/08/28 17:39:10]

const

[Anders Johnsen, 2014/08/29 07:11:37]

Cannot, I may reassign below.

+      if (limit > FLAG_optimization_counter_threshold) {
+        limit = FLAG_optimization_counter_threshold;
+      }
       __ incl(FieldAddress(function_reg, Function::usage_counter_offset()));
       __ cmpl(FieldAddress(function_reg, Function::usage_counter_offset()),
-              Immediate(FLAG_optimization_counter_threshold));
+              Immediate(limit));
     }
     ASSERT(function_reg == EDI);
     __ j(GREATER_EQUAL, &stub_code->OptimizeFunctionLabel());