libdispatch-187.5.tar.gz

[apple/libdispatch.git] / private / benchmark.h

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+/*
+ * Copyright (c) 2008-2009 Apple Inc. All rights reserved.
+ *
+ * @APPLE_APACHE_LICENSE_HEADER_START@
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ *
+ * @APPLE_APACHE_LICENSE_HEADER_END@
+ */
+
+/*
+ * IMPORTANT: This header file describes INTERNAL interfaces to libdispatch
+ * which are subject to change in future releases of Mac OS X. Any applications
+ * relying on these interfaces WILL break.
+ */
+
+#ifndef __DISPATCH_BENCHMARK__
+#define __DISPATCH_BENCHMARK__
+
+#ifndef __DISPATCH_INDIRECT__
+#error "Please #include <dispatch/dispatch.h> instead of this file directly."
+#include <dispatch/base.h> // for HeaderDoc
+#endif
+
+__BEGIN_DECLS
+
+/*!
+ * @function dispatch_benchmark
+ *
+ * @abstract
+ * Count the average number of cycles a given block takes to execute.
+ *
+ * @param count
+ * The number of times to serially execute the given block.
+ *
+ * @param block
+ * The block to execute.
+ *
+ * @result
+ * The approximate number of cycles the block takes to execute.
+ *
+ * @discussion
+ * This function is for debugging and performance analysis work. For the best
+ * results, pass a high count value to dispatch_benchmark(). When benchmarking
+ * concurrent code, please compare the serial version of the code against the
+ * concurrent version, and compare the concurrent version on different classes
+ * of hardware. Please look for inflection points with various data sets and
+ * keep the following facts in mind:
+ *
+ * 1) Code bound by computational bandwidth may be inferred by proportional
+ *    changes in performance as concurrency is increased.
+ * 2) Code bound by memory bandwidth may be inferred by negligible changes in
+ *    performance as concurrency is increased.
+ * 3) Code bound by critical sections may be inferred by retrograde changes in
+ *    performance as concurrency is increased.
+ * 3a) Intentional: locks, mutexes, and condition variables.
+ * 3b) Accidental: unrelated and frequently modified data on the same
+ *     cache-line.
+ */
+#ifdef __BLOCKS__
+__OSX_AVAILABLE_STARTING(__MAC_10_6,__IPHONE_4_0)
+DISPATCH_EXPORT DISPATCH_NONNULL2 DISPATCH_NOTHROW
+uint64_t
+dispatch_benchmark(size_t count, void (^block)(void));
+#endif
+
+__OSX_AVAILABLE_STARTING(__MAC_10_6,__IPHONE_4_0)
+DISPATCH_EXPORT DISPATCH_NONNULL3 DISPATCH_NOTHROW
+uint64_t
+dispatch_benchmark_f(size_t count, void *ctxt, void (*func)(void *));
+
+__END_DECLS
+
+#endif