Re: [PATCH] decide edge's hotness when there is profile info

[Teresa Johnson <tejohnson at google dot com>]

On Tue, Oct 15, 2013 at 3:39 PM, Teresa Johnson <tejohnson@google.com> wrote:
> On Tue, Oct 15, 2013 at 2:57 PM, Jan Hubicka <hubicka@ucw.cz> wrote:
>>> On Tue, Oct 15, 2013 at 2:03 PM, Jan Hubicka <hubicka@ucw.cz> wrote:
>>> >> Yes, that would work. So let's discard this patch because the fix for
>>> >> comdat can also fix this problem.
>>> >
>>> > Unforutnately ipa-profile-estimate is an IPA pass and as such it does
>>> > not have access to profile_status_to_function.
>>>
>>> I see. I was coding that up today but hadn't tested it yet.
>>>
>>> > You can probably just factor this out into a function that can be called
>>> > and for normal FDO we call it where the loop stis now and for auto-FDO we can
>>> > probably have another invocation from before early passes where auto-FDO is collected.
>>>
>>> Ok, let's go with that approach for now. It won't address the 0 count
>>> COMDAT calling another 0 count COMDAT problem, but I will probably
>>> just find a way to deal with this when inlining.
>>
>> You can still propagate, since tree-profile is an simple-ipa pass.
>
> Ok, I think I will leave that for the second patch, since I need to do
> some testing on the effects - i.e. the propagation I had in mind would
> make any 0-count routine called by a routine that was dropped to
> guessed to also be dropped to guessed (and no longer unlikely). It may
> be too aggressive, I need to check.
>
>>>
>>> >> >>> +      if (node->count)
>>> >> >>> + continue;
>>> > Also here we should sum the counts and consider function non unlikely executed
>>> > in the same way as probably_never_executed does.
>>>
>>> I assume you mean by doing the same comparison to the number of
>>> profile->runs. Yes, this makes sense.
>>
>> Yes.
>>>
>>> >
>>> > I can prepare updated patch, but i am currently travelling, so i would not
>>> > be disapointed if you beat me ;)
>>>
>>> I'm working on it, and I think based on Dehao's needs I am going to
>>> split up the patch into two phases, the one that does just the part
>>> you had sent a patch for (making sure 0 count routines with non-zero
>>> calls are marked guessed and have their node frequency set
>>> appropriately), and a subsequent one to do the count application when
>>> we inline a 0-count routine into a non-zero callsite. I'll shoot for
>>> getting this ready by tomorrow.
>>>
>>> BTW, in your original patch you are checking for both e->count or
>>> cgraph_maybe_hot_edge_p(e), but AFAICT the call to
>>> cgraph_maybe_hot_edge_p will never return true when e->count is zero.
>>> When there is a profile it will return false via maybe_hot_count_p
>>> since e->count == 0. When there is no profile it will return false
>>> when the callee has NODE_FREQUENCY_UNLIKELY_EXECUTED. So I think just
>>> checking for e->count >0 is sufficient here.
>>
>> I think I was checking caller count here (that is read) and the code
>> was supposed to make functoin with hot caller to be hot...
>
> The code in your patch was just checking the edge count, not the
> caller count. cgraph_maybe_hot_edge_p also doesn't check the caller
> count, just the edge count. Do we want to make all functions with hot
> callers also be hot, even when the edge count is not hot? This may be
> to aggressive. I was simply going to make the code check e->count.

Here is the patch from Honza, that I revised based on discussions and
testing. Once this related patch goes in, I can change the check against the
profile_info->runs that hardcodes the threshold with the new parameter
proposed for probably_never_executed there:
  http://gcc.gnu.org/ml/gcc-patches/2013-10/msg00743.html

Bootstrapped and tested on x86_64-unknown-linux-gnu. Ok for trunk?

Thanks, Teresa

2013-10-16  Jan Hubicka  <jh@suse.cz>
            Teresa Johnson  <tejohnson@google.com>

        * predict.c (handle_missing_profiles): New function.
        (counts_to_freqs): Don't overwrite estimated frequencies
        when function has no profile counts.
        * predict.h (handle_missing_profiles): Declare.
        * tree-profile.c (tree_profiling): Invoke handle_missing_profiles.

Index: predict.c
===================================================================
--- predict.c   (revision 203633)
+++ predict.c   (working copy)
@@ -2742,6 +2742,39 @@ estimate_loops (void)
   BITMAP_FREE (tovisit);
 }

+void
+handle_missing_profiles (void)
+{
+  struct cgraph_node *node;
+  /* See if 0 count function has non-0 count callers.  In this case we
+     lost some profile.  Drop its function profile to PROFILE_GUESSED.  */
+  FOR_EACH_DEFINED_FUNCTION (node)
+    {
+      struct cgraph_edge *e;
+      gcov_type call_count = 0;
+      struct function *fn = DECL_STRUCT_FUNCTION (node->symbol.decl);
+      if (node->count)
+        continue;
+      for (e = node->callers; e; e = e->next_caller)
+        call_count += e->count;
+      if (call_count
+          && fn && fn->cfg
+          && (call_count * 4 >= profile_info->runs))
+        {
+          bool maybe_hot = maybe_hot_count_p (NULL, call_count);
+          if (dump_file)
+            fprintf (dump_file,
+                     "Dropping 0 profile for %s/%i. %s based on calls.\n",
+                     cgraph_node_name (node), node->symbol.order,
+                     maybe_hot ? "Function is hot" : "Function is normal");
+          profile_status_for_function (fn)
+              = (flag_guess_branch_prob ? PROFILE_GUESSED : PROFILE_ABSENT);
+          node->frequency
+              = maybe_hot ? NODE_FREQUENCY_HOT : NODE_FREQUENCY_NORMAL;
+        }
+    }
+}
+
 /* Convert counts measured by profile driven feedback to frequencies.
    Return nonzero iff there was any nonzero execution count.  */

@@ -2751,6 +2784,9 @@ counts_to_freqs (void)
   gcov_type count_max, true_count_max = 0;
   basic_block bb;

+  if (!ENTRY_BLOCK_PTR->count)
+    return 0;
+
   FOR_BB_BETWEEN (bb, ENTRY_BLOCK_PTR, NULL, next_bb)
     true_count_max = MAX (bb->count, true_count_max);

Index: predict.h
===================================================================
--- predict.h   (revision 203633)
+++ predict.h   (working copy)
@@ -37,6 +37,7 @@ enum prediction

 extern void predict_insn_def (rtx, enum br_predictor, enum prediction);
 extern int counts_to_freqs (void);
+extern void handle_missing_profiles (void);
 extern void estimate_bb_frequencies (bool);
 extern const char *predictor_name (enum br_predictor);
 extern tree build_predict_expr (enum br_predictor, enum prediction);
Index: tree-profile.c
===================================================================
--- tree-profile.c      (revision 203633)
+++ tree-profile.c      (working copy)
@@ -607,6 +607,8 @@ tree_profiling (void)
       pop_cfun ();
     }

+  handle_missing_profiles ();
+
   del_node_map ();
   return 0;
 }


>
> Teresa
>
>>
>> Honza
>>>
>>> Thanks,
>>> Teresa
>>>
>>> >
>>> > Honza
>>>
>>>
>>>
>>> --
>>> Teresa Johnson | Software Engineer | tejohnson@google.com | 408-460-2413
>
>
>
> --
> Teresa Johnson | Software Engineer | tejohnson@google.com | 408-460-2413



-- 
Teresa Johnson | Software Engineer | tejohnson@google.com | 408-460-2413