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Commit ed277997 by Johannes Singler Committed by Johannes Singler
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partition.h (__parallel_partition): Improve scalability by... 

2010-04-22  Johannes Singler  <singler@kit.edu>

        * include/parallel/partition.h (__parallel_partition):
        Improve scalability by:
        -introducing new variables __leftold, __rightold, __dist, thus
        -getting rid of omp lock by using atomic operations
        -getting rid of two omp barriers

From-SVN: r158636
parent 6a0447ba
Showing with 79 additions and 75 deletions
libstdc++-v3/ChangeLog
2010-04-22 Johannes Singler <singler@kit.edu>
* include/parallel/partition.h (__parallel_partition):
Improve scalability by:
-introducing new variables __leftold, __rightold, __dist, thus
-getting rid of omp lock by using atomic operations
-getting rid of two omp barriers
2010-04-22 Jonathan Wakely <jwakely.gcc@gmail.com>
* doc/xml/faq.xml: Link to manual.
......
libstdc++-v3/include/parallel/partition.h
......@@ -66,27 +66,26 @@ namespace __gnu_parallel
const _Settings& __s = _Settings::get();
// Shared.
_GLIBCXX_VOLATILE _DifferenceType __left = 0, __right = __n - 1;
_GLIBCXX_VOLATILE _DifferenceType __leftover_left, __leftover_right;
_GLIBCXX_VOLATILE _DifferenceType __leftnew, __rightnew;
// shared
_GLIBCXX_VOLATILE _DifferenceType __left = 0, __right = __n - 1,
__dist = __n,
__leftover_left, __leftover_right,
__leftnew, __rightnew;
bool* __reserved_left = NULL, * __reserved_right = NULL;
// just 0 or 1, but int to allow atomic operations
int* __reserved_left = NULL, * __reserved_right = NULL;
_DifferenceType __chunk_size = __s.partition_chunk_size;
omp_lock_t __result_lock;
omp_init_lock(&__result_lock);
//at least two chunks per thread
if (__right - __left + 1 >= 2 * __num_threads * __chunk_size)
if (__dist >= 2 * __num_threads * __chunk_size)
# pragma omp parallel num_threads(__num_threads)
{
# pragma omp single
{
__num_threads = omp_get_num_threads();
__reserved_left = new bool[__num_threads];
__reserved_right = new bool[__num_threads];
__reserved_left = new int[__num_threads];
__reserved_right = new int[__num_threads];
if (__s.partition_chunk_share > 0.0)
__chunk_size = std::max<_DifferenceType>
......@@ -96,17 +95,16 @@ namespace __gnu_parallel
__chunk_size = __s.partition_chunk_size;
}
while (__right - __left + 1 >= 2 * __num_threads * __chunk_size)
while (__dist >= 2 * __num_threads * __chunk_size)
{
# pragma omp single
{
_DifferenceType __num_chunks = ((__right - __left + 1)
/ __chunk_size);
_DifferenceType __num_chunks = __dist / __chunk_size;
for (_ThreadIndex __r = 0; __r < __num_threads; ++__r)
{
__reserved_left[__r] = false;
__reserved_right[__r] = false;
__reserved_left [__r] = 0; // false
__reserved_right[__r] = 0; // false
}
__leftover_left = 0;
__leftover_right = 0;
......@@ -115,11 +113,13 @@ namespace __gnu_parallel
// Private.
_DifferenceType __thread_left, __thread_left_border,
__thread_right, __thread_right_border;
__thread_left = __left + 1;
__thread_left = __left + 1;
// Just to satisfy the condition below.
__thread_left_border = __thread_left - 1;
__thread_right = __n - 1;
// Just to satisfy the condition below.
__thread_right_border = __thread_right + 1;
bool __iam_finished = false;
......@@ -127,35 +127,42 @@ namespace __gnu_parallel
{
if (__thread_left > __thread_left_border)
{
omp_set_lock(&__result_lock);
if (__left + (__chunk_size - 1) > __right)
__iam_finished = true;
else
{
__thread_left = __left;
__thread_left_border = __left + (__chunk_size - 1);
__left += __chunk_size;
}
omp_unset_lock(&__result_lock);
_DifferenceType __former_dist =
__fetch_and_add(&__dist, -__chunk_size);
if (__former_dist < __chunk_size)
{
__fetch_and_add(&__dist, __chunk_size);
__iam_finished = true;
break;
}
else
{
__thread_left =
__fetch_and_add(&__left, __chunk_size);
__thread_left_border =
__thread_left + (__chunk_size - 1);
}
}
if (__thread_right < __thread_right_border)
{
omp_set_lock(&__result_lock);
if (__left > __right - (__chunk_size - 1))
__iam_finished = true;
else
{
__thread_right = __right;
__thread_right_border = __right - (__chunk_size - 1);
__right -= __chunk_size;
}
omp_unset_lock(&__result_lock);
_DifferenceType __former_dist =
__fetch_and_add(&__dist, -__chunk_size);
if (__former_dist < __chunk_size)
{
__fetch_and_add(&__dist, __chunk_size);
__iam_finished = true;
break;
}
else
{
__thread_right =
__fetch_and_add(&__right, -__chunk_size);
__thread_right_border =
__thread_right - (__chunk_size - 1);
}
}
if (__iam_finished)
break;
// Swap as usual.
while (__thread_left < __thread_right)
{
......@@ -188,13 +195,11 @@ namespace __gnu_parallel
# pragma omp barrier
# pragma omp single
{
__leftnew = __left - __leftover_left * __chunk_size;
__rightnew = __right + __leftover_right * __chunk_size;
}
# pragma omp barrier
_DifferenceType
__leftold = __left,
__leftnew = __left - __leftover_left * __chunk_size,
__rightold = __right,
__rightnew = __right + __leftover_right * __chunk_size;
// <=> __thread_left_border + (__chunk_size - 1) >= __leftnew
if (__thread_left <= __thread_left_border
......@@ -202,7 +207,7 @@ namespace __gnu_parallel
{
// Chunk already in place, reserve spot.
__reserved_left[(__left - (__thread_left_border + 1))
/ __chunk_size] = true;
/ __chunk_size] = 1;
}
// <=> __thread_right_border - (__chunk_size - 1) <= __rightnew
......@@ -211,7 +216,7 @@ namespace __gnu_parallel
{
// Chunk already in place, reserve spot.
__reserved_right[((__thread_right_border - 1) - __right)
/ __chunk_size] = true;
/ __chunk_size] = 1;
}
# pragma omp barrier
......@@ -221,15 +226,13 @@ namespace __gnu_parallel
{
// Find spot and swap.
_DifferenceType __swapstart = -1;
omp_set_lock(&__result_lock);
for (_DifferenceType __r = 0; __r < __leftover_left; ++__r)
if (!__reserved_left[__r])
{
__reserved_left[__r] = true;
__swapstart = __left - (__r + 1) * __chunk_size;
break;
}
omp_unset_lock(&__result_lock);
for (int __r = 0; __r < __leftover_left; ++__r)
if (__reserved_left[__r] == 0
&& __compare_and_swap(&(__reserved_left[__r]), 0, 1))
{
__swapstart = __leftold - (__r + 1) * __chunk_size;
break;
}
#if _GLIBCXX_ASSERTIONS
_GLIBCXX_PARALLEL_ASSERT(__swapstart != -1);
......@@ -246,15 +249,13 @@ namespace __gnu_parallel
{
// Find spot and swap
_DifferenceType __swapstart = -1;
omp_set_lock(&__result_lock);
for (_DifferenceType __r = 0; __r < __leftover_right; ++__r)
if (!__reserved_right[__r])
{
__reserved_right[__r] = true;
__swapstart = __right + __r * __chunk_size + 1;
break;
}
omp_unset_lock(&__result_lock);
for (int __r = 0; __r < __leftover_right; ++__r)
if (__reserved_right[__r] == 0
&& __compare_and_swap(&(__reserved_right[__r]), 0, 1))
{
__swapstart = __rightold + __r * __chunk_size + 1;
break;
}
#if _GLIBCXX_ASSERTIONS
_GLIBCXX_PARALLEL_ASSERT(__swapstart != -1);
......@@ -270,18 +271,15 @@ namespace __gnu_parallel
# pragma omp single
{
for (_DifferenceType __r = 0; __r < __leftover_left; ++__r)
_GLIBCXX_PARALLEL_ASSERT(__reserved_left[__r]);
_GLIBCXX_PARALLEL_ASSERT(__reserved_left[__r] == 1);
for (_DifferenceType __r = 0; __r < __leftover_right; ++__r)
_GLIBCXX_PARALLEL_ASSERT(__reserved_right[__r]);
_GLIBCXX_PARALLEL_ASSERT(__reserved_right[__r] == 1);
}
# pragma omp barrier
#endif
# pragma omp barrier
__left = __leftnew;
__right = __rightnew;
__dist = __right - __left + 1;
}
# pragma omp flush(__left, __right)
......@@ -313,8 +311,6 @@ namespace __gnu_parallel
delete[] __reserved_left;
delete[] __reserved_right;
omp_destroy_lock(&__result_lock);
// Element "between" __final_left and __final_right might not have
// been regarded yet
if (__final_left < __n && !__pred(__begin[__final_left]))
......
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