Set default blocktime to 0 for hybrid CPU

[Nawrin]

Summary

This patch sets the default KMP_BLOCKTIME to 0 for hybrid CPUs. For hybrid CPU, setting default blocktime to 0 provides better performance in some large benchmarks (OMP2012, CPU2017). More investigation regarding impact on performance is on-going.

[AndreyChurbanov]

LGTM

openmp/runtime/src/kmp.h

 #define KMP_MIN_STKPADDING (0)
 #define KMP_MAX_STKPADDING (2 * 1024 * 1024)
 
 #define KMP_BLOCKTIME_MULTIPLIER                                               \
   (1000) /* number of blocktime units per second */
 #define KMP_MIN_BLOCKTIME (0)
 #define KMP_MAX_BLOCKTIME                                                      \
   (INT_MAX) /* Must be this for "infinite" setting the work */
-#define KMP_DEFAULT_BLOCKTIME (200) /*  __kmp_blocktime is in milliseconds  */
+
+/* __kmp_blocktime is in milliseconds */
+#define KMP_DEFAULT_BLOCKTIME (__kmp_is_hybrid_cpu() ? (0) : (200))
 
 #if KMP_USE_MONITOR
 #define KMP_DEFAULT_MONITOR_STKSIZE ((size_t)(64 * 1024))
 #define KMP_MIN_MONITOR_WAKEUPS (1) // min times monitor wakes up per second
 #define KMP_MAX_MONITOR_WAKEUPS (1000) // max times monitor can wake up per sec
 
 /* Calculate new number of monitor wakeups for a specific block time based on
    previous monitor_wakeups. Only allow increasing number of wakeups */