Re: [Bug libstdc++/54075] [4.7.1] unordered_map insert still slower than 4.6.2

[François Dumont <frs dot dumont at gmail dot com>]

Attached patch applied.

2012-11-16  François Dumont  <fdumont@gcc.gnu.org>

    * include/bits/hashtable_policy.h (_Prime_rehash_policy): Remove
    automatic shrink.
    (_Prime_rehash_policy::_M_bkt_for_elements): Do not call
    _M_next_bkt anymore.
    (_Prime_rehash_policy::_M_next_bkt): Move usage of
    _S_growth_factor ...
    (_Prime_rehash_policy::_M_need_rehash): ... here.
    * include/bits/hashtable.h (_Hashtable<>): Adapt.
    * testsuite/performance/23_containers/insert_erase/41975.cc: Add
    _USE_TR1 to force build using std::tr1 container.
    * testsuite/performance/23_containers/insert/unordered_set.cc:
    Likewise.
    * testsuite/performance/23_containers/insert/54075.cc: New.

Note that I have used std::random_device in 54075 test. I also preferred 
to test both std and std::tr1 containers in a single run without relying 
on a macro check. As long as we try to align std containers performance 
on tr1 ones it is better maybe later we could limit it to test only 
std:: container per default.

I have also added several use cases and here is the result:

54075.cc                     std::tr1::unordered_set without hash code 
cached 300000 Foo insertions      10r    9u    1s 13765616mem    0pf
54075.cc                     std::tr1::unordered_set without hash code 
cached 10 times insertion of 300000 Foo      21r   21u 0s        0mem    
0pf
54075.cc                     std::tr1::unordered_set with hash code 
cached 300000 Foo insertions      15r   14u    0s 18561984mem    0pf
54075.cc                     std::tr1::unordered_set with hash code 
cached 10 times insertion of 300000 Foo      23r   23u 0s        0mem    
0pf
54075.cc                     std::tr1::unordered_multiset without hash 
code cached 300000 Foo insertions       9r    8u    1s 13761968mem    0pf
54075.cc                     std::tr1::unordered_multiset without hash 
code cached 10 times insertion of 300000 Foo     113r 107u    7s 
126686848mem    0pf
54075.cc                     std::tr1::unordered_multiset with hash code 
cached 300000 Foo insertions     100r  100u    0s 18561984mem    0pf
54075.cc                     std::tr1::unordered_multiset with hash code 
cached 10 times insertion of 300000 Foo     111r 107u    4s 
174686864mem    0pf
54075.cc                     std::unordered_set without hash code cached 
300000 Foo insertions       9r    8u    1s 13761936mem 0pf
54075.cc                     std::unordered_set without hash code cached 
10 times insertion of 300000 Foo      34r   34u 0s        0mem    0pf
54075.cc                     std::unordered_set with hash code cached 
300000 Foo insertions      10r   10u    1s 18562000mem 0pf
54075.cc                     std::unordered_set with hash code cached 10 
times insertion of 300000 Foo      37r   37u 0s        0mem    0pf
54075.cc                     std::unordered_multiset without hash code 
cached 300000 Foo insertions       8r    9u    0s 13761936mem    0pf
54075.cc                     std::unordered_multiset without hash code 
cached 10 times insertion of 300000 Foo      34r   34u 0s        0mem    
0pf
54075.cc                     std::unordered_multiset with hash code 
cached 300000 Foo insertions      10r   10u    0s 18562000mem    0pf
54075.cc                     std::unordered_multiset with hash code 
cached 10 times insertion of 300000 Foo      37r   37u 0s        0mem    
0pf

    There is one surprising result; std::tr1::unordered_multiset is 
quite bad, I haven't check yet why and it is not my priority, I take it 
as a good news for the moment. The other important result is this one:
54075.cc                     std::tr1::unordered_set without hash code 
cached 10 times insertion of 300000 Foo      21r   21u 0s        0mem    0pf
54075.cc                     std::unordered_set without hash code cached 
10 times insertion of 300000 Foo      34r   34u 0s        0mem    0pf

    We can see that inserting the same elements again, that is to say 
detecting the collisions, is slower in the new implementation. It is the 
problem I had already signaled in bugzilla entry. In the new 
implementation when we need to look for bucket elements we have to check 
the hash code of each element to see if we are still in the same bucket, 
in the former there was a nullptr to signal the end of the bucket. I 
think I am going to try to add an empty node to mark the end of the 
bucket. It will introduce a memory tradeoff of one empty node for each 
non-empty bucket but it will also limit the impact of caching the hash 
code or node because we won't need to use it so often.

François



On 11/14/2012 11:54 AM, Paolo Carlini wrote:
> Hi,
>
> On 11/13/2012 10:40 PM, François Dumont wrote:
> > 2012-11-13 François Dumont <fdumont@gcc.gnu.org>
> >
> >     * include/bits/hashtable_policy.h (_Prime_rehash_policy): Remove
> >     automatic shrink.
> >     (_Prime_rehash_policy::_M_bkt_for_elements): Do not call
> >     _M_next_bkt anymore.
> >     (_Prime_rehash_policy::_M_next_bkt): Move usage of
> >     _S_growth_factor ...
> >     (_Prime_rehash_policy::_M_need_rehash): ... here.
> >     * include/bits/hashtable.h (_Hashtable<>): Adapt.
> >
> > Tested under linux x86_64, normal and debug modes.
> Patch is Ok with me, please wait another day or two for comments and 
> then apply it.
>
> You can also add the performance testcase, of course, note however 
> that ::random isn't a standard C function, thus we shouldn't use it 
> unconditionally, either manage with std::rand from <cstdlib> or do 
> something completely different (maybe even <random> since you are 
> writing C++11 code anyway!). I would also recommend extending quite a 
> bit the runtime, 10x would be still completely sensible (but I guess, 
> without using much more memory)
>
> Paolo.

Index: include/bits/hashtable.h
===================================================================
--- include/bits/hashtable.h	(revision 193575)
+++ include/bits/hashtable.h	(working copy)
@@ -806,11 +806,6 @@
       _M_rehash_policy()
     {
       _M_bucket_count = _M_rehash_policy._M_next_bkt(__bucket_hint);
-
-      // We don't want the rehash policy to ask for the hashtable to
-      // shrink on the first insertion so we need to reset its
-      // previous resize level.
-      _M_rehash_policy._M_prev_resize = 0;
       _M_buckets = _M_allocate_buckets(_M_bucket_count);
     }
 
@@ -834,16 +829,12 @@
 	_M_element_count(0),
 	_M_rehash_policy()
       {
+	auto __nb_elems = __detail::__distance_fw(__f, __l);
 	_M_bucket_count =
-	  _M_rehash_policy._M_bkt_for_elements(__detail::__distance_fw(__f,
-								       __l));
-	if (_M_bucket_count <= __bucket_hint)
-	  _M_bucket_count = _M_rehash_policy._M_next_bkt(__bucket_hint);
+	  _M_rehash_policy._M_next_bkt(
+	    std::max(_M_rehash_policy._M_bkt_for_elements(__nb_elems),
+		     __bucket_hint));
 
-	// We don't want the rehash policy to ask for the hashtable to
-	// shrink on the first insertion so we need to reset its
-	// previous resize level.
-	_M_rehash_policy._M_prev_resize = 0;
 	_M_buckets = _M_allocate_buckets(_M_bucket_count);
 	__try
 	  {
@@ -990,6 +981,7 @@
     __rehash_policy(const _RehashPolicy& __pol)
     {
       size_type __n_bkt = __pol._M_bkt_for_elements(_M_element_count);
+      __n_bkt = __pol._M_next_bkt(__n_bkt);
       if (__n_bkt != _M_bucket_count)
 	_M_rehash(__n_bkt, _M_rehash_policy._M_state());
       _M_rehash_policy = __pol;
@@ -1641,19 +1633,12 @@
     {
       const __rehash_state& __saved_state = _M_rehash_policy._M_state();
       std::size_t __buckets
-	= _M_rehash_policy._M_bkt_for_elements(_M_element_count + 1);
-      if (__buckets <= __n)
-	__buckets = _M_rehash_policy._M_next_bkt(__n);
+	= std::max(_M_rehash_policy._M_bkt_for_elements(_M_element_count + 1),
+		   __n);
+      __buckets = _M_rehash_policy._M_next_bkt(__buckets);
 
       if (__buckets != _M_bucket_count)
-	{
-	  _M_rehash(__buckets, __saved_state);
-
-	  // We don't want the rehash policy to ask for the hashtable to shrink
-	  // on the next insertion so we need to reset its previous resize
-	  // level.
-	  _M_rehash_policy._M_prev_resize = 0;
-	}
+	_M_rehash(__buckets, __saved_state);
       else
 	// No rehash, restore previous state to keep a consistent state.
 	_M_rehash_policy._M_reset(__saved_state);
Index: include/bits/hashtable_policy.h
===================================================================
--- include/bits/hashtable_policy.h	(revision 193575)
+++ include/bits/hashtable_policy.h	(working copy)
@@ -358,7 +358,7 @@
   struct _Prime_rehash_policy
   {
     _Prime_rehash_policy(float __z = 1.0)
-    : _M_max_load_factor(__z), _M_prev_resize(0), _M_next_resize(0) { }
+    : _M_max_load_factor(__z), _M_next_resize(0) { }
 
     float
     max_load_factor() const noexcept
@@ -380,25 +380,21 @@
     _M_need_rehash(std::size_t __n_bkt, std::size_t __n_elt,
 		   std::size_t __n_ins) const;
 
-    typedef std::pair<std::size_t, std::size_t> _State;
+    typedef std::size_t _State;
 
     _State
     _M_state() const
-    { return std::make_pair(_M_prev_resize, _M_next_resize); }
+    { return _M_next_resize; }
 
     void
-    _M_reset(const _State& __state)
-    {
-      _M_prev_resize = __state.first;
-      _M_next_resize = __state.second;
-    }
+    _M_reset(_State __state)
+    { _M_next_resize = __state; }
 
     enum { _S_n_primes = sizeof(unsigned long) != 8 ? 256 : 256 + 48 };
 
     static const std::size_t _S_growth_factor = 2;
 
     float                _M_max_load_factor;
-    mutable std::size_t  _M_prev_resize;
     mutable std::size_t  _M_next_resize;
   };
 
@@ -417,35 +413,28 @@
     static const unsigned char __fast_bkt[12]
       = { 2, 2, 2, 3, 5, 5, 7, 7, 11, 11, 11, 11 };
 
-    const std::size_t __grown_n = __n * _S_growth_factor;
-    if (__grown_n <= 11)
+    if (__n <= 11)
       {
-	_M_prev_resize = 0;
 	_M_next_resize
-	  = __builtin_ceil(__fast_bkt[__grown_n]
+	  = __builtin_ceil(__fast_bkt[__n]
 			   * (long double)_M_max_load_factor);
-	return __fast_bkt[__grown_n];
+	return __fast_bkt[__n];
       }
 
     const unsigned long* __next_bkt
       = std::lower_bound(__prime_list + 5, __prime_list + _S_n_primes,
-			 __grown_n);
-    const unsigned long* __prev_bkt
-      = std::lower_bound(__prime_list + 1, __next_bkt, __n / _S_growth_factor);
-
-    _M_prev_resize
-      = __builtin_floor(*(__prev_bkt - 1) * (long double)_M_max_load_factor);
+			 __n);
     _M_next_resize
       = __builtin_ceil(*__next_bkt * (long double)_M_max_load_factor);
     return *__next_bkt;
   }
 
-  // Return the smallest prime p such that alpha p >= n, where alpha
+  // Return the smallest integer p such that alpha p >= n, where alpha
   // is the load factor.
   inline std::size_t
   _Prime_rehash_policy::
   _M_bkt_for_elements(std::size_t __n) const
-  { return _M_next_bkt(__builtin_ceil(__n / (long double)_M_max_load_factor)); }
+  { return __builtin_ceil(__n / (long double)_M_max_load_factor); }
 
   // Finds the smallest prime p such that alpha p > __n_elt + __n_ins.
   // If p > __n_bkt, return make_pair(true, p); otherwise return
@@ -467,7 +456,8 @@
 				 / (long double)_M_max_load_factor;
 	if (__min_bkts >= __n_bkt)
 	  return std::make_pair(true,
-				_M_next_bkt(__builtin_floor(__min_bkts) + 1));
+	    _M_next_bkt(std::max<std::size_t>(__builtin_floor(__min_bkts) + 1,
+					      __n_bkt * _S_growth_factor)));
 	else
 	  {
 	    _M_next_resize
@@ -475,13 +465,6 @@
 	    return std::make_pair(false, 0);
 	  }
       }
-    else if (__n_elt + __n_ins < _M_prev_resize)
-      {
-	long double __min_bkts = (__n_elt + __n_ins)
-				 / (long double)_M_max_load_factor;
-	return std::make_pair(true,
-			      _M_next_bkt(__builtin_floor(__min_bkts) + 1));
-      }
     else
       return std::make_pair(false, 0);
   }
Index: testsuite/performance/23_containers/insert_erase/41975.cc
===================================================================
--- testsuite/performance/23_containers/insert_erase/41975.cc	(revision 193575)
+++ testsuite/performance/23_containers/insert_erase/41975.cc	(working copy)
@@ -18,7 +18,11 @@
 // <http://www.gnu.org/licenses/>.
 
 #include <sstream>
-#include <unordered_set>
+#ifdef _USE_TR1
+#  include <tr1/unordered_set>
+#else
+#  include <unordered_set>
+#endif
 #include <testsuite_performance.h>
 
 namespace
@@ -40,11 +44,17 @@
       const int nb = 200000;
       start_counters(time, resource);
 
+#ifdef _USE_TR1
+      std::tr1::__unordered_set<int, std::hash<int>, std::equal_to<int>,
+				std::allocator<int>,
+			       	use_cache> us;
+#else
       std::__uset_hashtable<int, std::hash<int>, std::equal_to<int>,
 			    std::allocator<int>,
 			    std::__uset_traits<use_cache>> us;
+#endif
       for (int i = 0; i != nb; ++i)
-	us.insert(i);
+	  us.insert(i);
 
       stop_counters(time, resource);
       ostr.str("");
@@ -126,10 +136,17 @@
 
       start_counters(time, resource);
 
+#ifdef _USE_TR1
+      std::tr1::__unordered_set<std::string, std::hash<std::string>,
+				std::equal_to<std::string>,
+				std::allocator<std::string>,
+				use_cache> us;
+#else
       std::__uset_hashtable<std::string, std::hash<std::string>,
 			    std::equal_to<std::string>,
 			    std::allocator<std::string>,
 			    std::__uset_traits<use_cache>> us;
+#endif
       for (int i = 0; i != nb; ++i)
 	us.insert(strs[i]);
 
Index: testsuite/performance/23_containers/insert/unordered_set.cc
===================================================================
--- testsuite/performance/23_containers/insert/unordered_set.cc	(revision 193575)
+++ testsuite/performance/23_containers/insert/unordered_set.cc	(working copy)
@@ -17,8 +17,17 @@
 
 // { dg-options "-std=c++11" }
 
-#include <unordered_set>
 #include <testsuite_performance.h>
+#include <sstream>
+#ifdef _USE_TR1
+#  include <tr1/unordered_set>
+using namespace std::tr1;
+const char* ns = "std::tr1::";
+#else
+#  include<unordered_set>
+using namespace std;
+const char* ns = "std::";
+#endif
 
 int main()
 {
@@ -29,14 +38,16 @@
 
   const int sz = 10000000;
 
-  std::unordered_set<int> s;
+  unordered_set<int> s;
   start_counters(time, resource);
 
   for (int i = 0; i != sz ; ++i)
     s.insert(i);
 
   stop_counters(time, resource);
-  report_performance(__FILE__, "unordered_set 10000000 insertions",
+  std::ostringstream ostr;
+  ostr << ns << "unordered_set " << sz << " insertions";
+  report_performance(__FILE__, ostr.str().c_str(),
 		     time, resource);
   return 0;
 }
Index: testsuite/performance/23_containers/insert/54075.cc
===================================================================
--- testsuite/performance/23_containers/insert/54075.cc	(revision 0)
+++ testsuite/performance/23_containers/insert/54075.cc	(revision 0)
@@ -0,0 +1,132 @@
+// Copyright (C) 2012 Free Software Foundation, Inc.
+//
+// This file is part of the GNU ISO C++ Library.  This library is free
+// software; you can redistribute it and/or modify it under the
+// terms of the GNU General Public License as published by the
+// Free Software Foundation; either version 3, or (at your option)
+// any later version.
+
+// This library is distributed in the hope that it will be useful,
+// but WITHOUT ANY WARRANTY; without even the implied warranty of
+// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+// GNU General Public License for more details.
+
+// You should have received a copy of the GNU General Public License along
+// with this library; see the file COPYING3.  If not see
+// <http://www.gnu.org/licenses/>.
+
+// { dg-options "-std=c++11" }
+
+#include <testsuite_performance.h>
+#include <random>
+#include <sstream>
+#include <tr1/unordered_set>
+#include<unordered_set>
+
+struct Foo
+{
+  typedef std::random_device::result_type _Type;
+  _Type bar;
+  _Type baz;
+  _Type meh;
+
+  void
+  init(std::random_device& randev)
+  {
+    bar = randev();
+    baz = randev();
+    meh = randev();
+  }
+
+  std::size_t
+  hash() const noexcept
+  { return std::size_t(bar ^ baz ^ meh); }
+
+  inline bool
+  operator==(const Foo& other) const
+  { return other.bar == bar && other.baz == baz && other.meh == meh; }
+};
+
+struct HashFunction
+{
+  template<typename T>
+    std::size_t operator()(const T& t) const noexcept
+    { return t.hash(); }
+};
+
+template<typename _ContType>
+  void bench(const char* container_desc)
+  {
+    using namespace __gnu_test;
+
+    time_counter time;
+    resource_counter resource;
+
+    const int sz = 300000;
+
+    Foo foos[sz];
+    {
+      std::random_device randev;
+      for (int i = 0; i != sz; ++i)
+	foos[i].init(randev);
+    }
+
+    _ContType s;
+    start_counters(time, resource);
+
+    for (int i = 0; i != sz ; ++i)
+      s.insert(foos[i]);
+
+    stop_counters(time, resource);
+    std::ostringstream ostr;
+    ostr << container_desc << sz << " Foo insertions";
+    report_performance(__FILE__, ostr.str().c_str(), time, resource);
+
+    // Try to insert again to check performance of collision detection
+    
+    const int nb_loop = 10;
+    start_counters(time, resource);
+
+    for (int j = 0; j != nb_loop; ++j)
+      for (int i = 0; i != sz; ++i)
+	s.insert(foos[i]);
+
+    stop_counters(time, resource);
+    ostr.str("");
+    ostr << container_desc << nb_loop << " times insertion of "
+	 << sz << " Foo";
+    report_performance(__FILE__, ostr.str().c_str(), time, resource);
+  }
+
+template<bool cache>
+  using __tr1_uset = std::tr1::__unordered_set<Foo, HashFunction,
+					       std::equal_to<Foo>,
+					       std::allocator<Foo>,
+					       cache>;
+template<bool cache>
+  using __tr1_umset = std::tr1::__unordered_multiset<Foo, HashFunction,
+						     std::equal_to<Foo>,
+						     std::allocator<Foo>,
+						     cache>;
+template<bool cache>
+  using __uset = std::__uset_hashtable<Foo, HashFunction,
+				       std::equal_to<Foo>,
+				       std::allocator<Foo>,
+				       std::__uset_traits<cache>>;
+template<bool cache>
+  using __umset = std::__umset_hashtable<Foo, HashFunction,
+					 std::equal_to<Foo>,
+					 std::allocator<Foo>,
+					 std::__uset_traits<cache>>;
+
+int main()
+{
+  bench<__tr1_uset<false>>("std::tr1::unordered_set without hash code cached ");
+  bench<__tr1_uset<true>>("std::tr1::unordered_set with hash code cached ");
+  bench<__tr1_umset<false>>("std::tr1::unordered_multiset without hash code cached ");
+  bench<__tr1_umset<true>>("std::tr1::unordered_multiset with hash code cached ");
+  bench<__uset<false>>("std::unordered_set without hash code cached ");
+  bench<__uset<true>>("std::unordered_set with hash code cached ");
+  bench<__umset<false>>("std::unordered_multiset without hash code cached ");
+  bench<__umset<true>>("std::unordered_multiset with hash code cached ");
+}