On ARM platform, use yield op to relax CPU. See issue 7376 (#7438)

Summary:
see https://github.com/facebook/rocksdb/issues/7376.
The `wfe` op on ARM platform is not suitable to relax CPU. Use `yield` op.

Pull Request resolved: https://github.com/facebook/rocksdb/pull/7438

Reviewed By: riversand963

Differential Revision: D24063427

Pulled By: jay-zhuang

fbshipit-source-id: b0ebc5590d7555bd21b30f15cd59f84dc006367a

HISTORY.md

@@ -6,6 +6,9 @@
 ### Bug Fixes
 * Use thread-safe `strerror_r()` to get error messages.
 
+### Performance Improvements
+* On ARM platform, use `yield` instead of `wfe` to relax cpu to gain better performance.
+
 ## 6.19.0 (03/21/2021)
 ### Bug Fixes
 * Fixed the truncation error found in APIs/tools when dumping block-based SST files in a human-readable format. After fix, the block-based table can be fully dumped as a readable file.
@@ -143,6 +146,7 @@
 * The settings of the DBOptions and ColumnFamilyOptions are now managed by Configurable objects (see New Features).  The same convenience methods to configure these options still exist but the backend implementation has been unified under a common implementation.
 
 ### New Features
+
 * Methods to configure serialize, and compare -- such as TableFactory -- are exposed directly through the Configurable base class (from which these objects inherit).  This change will allow for better and more thorough configuration management and retrieval in the future.  The options for a Configurable object can be set via the ConfigureFromMap, ConfigureFromString, or ConfigureOption method.  The serialized version of the options of an object can be retrieved via the GetOptionString, ToString, or GetOption methods.  The list of options supported by an object can be obtained via the GetOptionNames method.  The "raw" object (such as the BlockBasedTableOption) for an option may be retrieved via the GetOptions method.  Configurable options can be compared via the AreEquivalent method.  The settings within a Configurable object may be validated via the ValidateOptions method.  The object may be intialized (at which point only mutable options may be updated) via the PrepareOptions method.
 * Introduce options.check_flush_compaction_key_order with default value to be true. With this option, during flush and compaction, key order will be checked when writing to each SST file. If the order is violated, the flush or compaction will fail.
 * Added is_full_compaction to CompactionJobStats, so that the information is available through the EventListener interface.

port/port_posix.h

@@ -167,7 +167,7 @@ static inline void AsmVolatilePause() {
 #if defined(__i386__) || defined(__x86_64__)
   asm volatile("pause");
 #elif defined(__aarch64__)
-  asm volatile("wfe");
+  asm volatile("yield");
 #elif defined(__powerpc64__)
   asm volatile("or 27,27,27");
 #endif