377aa40d84
This change adds back off logic in the test and set lock for better contended
lock performance. It uses a simple truncated binary exponential back off
function. The default back off parameters are tuned for x86.
The main back off logic has a two loop structure where each is controlled by a
user-level parameter:
max_backoff - limits the outer loop number of iterations.
This parameter should be a power of 2.
min_ticks - the inner spin wait loop number of "ticks" which is system
dependent and should be tuned for your system if you so choose.
The "ticks" on x86 correspond to the time stamp counter,
but on other architectures ticks is a timestamp derived
from gettimeofday().
The user can modify these via the environment variable:
KMP_SPIN_BACKOFF_PARAMS=max_backoff[,min_ticks]
Currently, since the default user lock is a queuing lock,
one would have to also specify KMP_LOCK_KIND=tas to use the test-and-set locks.
Differential Revision: http://reviews.llvm.org/D19020
llvm-svn: 266329
47 lines
912 B
C
47 lines
912 B
C
// RUN: %libomp-compile-and-run
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// RUN: %libomp-compile && env KMP_LOCK_KIND=tas KMP_SPIN_BACKOFF_PARAMS=2048,200 %libomp-run
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#include <stdio.h>
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#include "omp_testsuite.h"
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omp_lock_t lck;
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int test_omp_lock()
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{
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int nr_threads_in_single = 0;
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int result = 0;
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int nr_iterations = 0;
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int i;
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omp_init_lock(&lck);
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#pragma omp parallel shared(lck)
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{
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#pragma omp for
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for(i = 0; i < LOOPCOUNT; i++) {
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omp_set_lock(&lck);
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#pragma omp flush
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nr_threads_in_single++;
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#pragma omp flush
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nr_iterations++;
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nr_threads_in_single--;
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result = result + nr_threads_in_single;
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omp_unset_lock(&lck);
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}
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}
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omp_destroy_lock(&lck);
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return ((result == 0) && (nr_iterations == LOOPCOUNT));
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}
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int main()
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{
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int i;
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int num_failed=0;
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for(i = 0; i < REPETITIONS; i++) {
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if(!test_omp_lock()) {
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num_failed++;
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}
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}
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return num_failed;
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}
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