--- a/src/hotspot/cpu/ppc/assembler_ppc.inline.hpp	Tue Apr 10 09:12:23 2018 +0200
+++ b/src/hotspot/cpu/ppc/assembler_ppc.inline.hpp	Thu Apr 05 20:09:33 2018 -0400
@@ -620,7 +620,7 @@
 inline void Assembler::stqcx_(Register s, Register a, Register b)                             { emit_int32( STQCX_OPCODE | rs(s) | ra0mem(a) | rb(b) | rc(1)); }
 
 // Instructions for adjusting thread priority
-// for simultaneous multithreading (SMT) on POWER5.
+// for simultaneous multithreading (SMT) on >= POWER5.
 inline void Assembler::smt_prio_very_low()    { Assembler::or_unchecked(R31, R31, R31); }
 inline void Assembler::smt_prio_low()         { Assembler::or_unchecked(R1,  R1,  R1); }
 inline void Assembler::smt_prio_medium_low()  { Assembler::or_unchecked(R6,  R6,  R6); }
@@ -628,11 +628,11 @@
 inline void Assembler::smt_prio_medium_high() { Assembler::or_unchecked(R5,  R5,  R5); }
 inline void Assembler::smt_prio_high()        { Assembler::or_unchecked(R3,  R3,  R3); }
 // >= Power7
-inline void Assembler::smt_yield()            { Assembler::or_unchecked(R27, R27, R27); }
-inline void Assembler::smt_mdoio()            { Assembler::or_unchecked(R29, R29, R29); }
-inline void Assembler::smt_mdoom()            { Assembler::or_unchecked(R30, R30, R30); }
-// >= Power8
-inline void Assembler::smt_miso()             { Assembler::or_unchecked(R26, R26, R26); }
+inline void Assembler::smt_yield()            { Assembler::or_unchecked(R27, R27, R27); } // never actually implemented
+inline void Assembler::smt_mdoio()            { Assembler::or_unchecked(R29, R29, R29); } // never actually implemetned
+inline void Assembler::smt_mdoom()            { Assembler::or_unchecked(R30, R30, R30); } // never actually implemented
+// Power8
+inline void Assembler::smt_miso()             { Assembler::or_unchecked(R26, R26, R26); } // never actually implemented
 
 inline void Assembler::twi_0(Register a)      { twi_unchecked(0, a, 0);}
 

--- a/src/hotspot/cpu/ppc/macroAssembler_ppc.cpp	Tue Apr 10 09:12:23 2018 +0200
+++ b/src/hotspot/cpu/ppc/macroAssembler_ppc.cpp	Thu Apr 05 20:09:33 2018 -0400
@@ -2579,7 +2579,6 @@
   if (checkRetry) { bind(*checkRetry); }
   addic_(retry_count_Reg, retry_count_Reg, -1);
   blt(CCR0, doneRetry);
-  smt_yield(); // Can't use wait(). No permission (SIGILL).
   b(retryLabel);
   bind(doneRetry);
 }
@@ -2590,7 +2589,7 @@
 // output: retry_count_Reg decremented by 1
 // CTR is killed
 void MacroAssembler::rtm_retry_lock_on_busy(Register retry_count_Reg, Register owner_addr_Reg, Label& retryLabel) {
-  Label SpinLoop, doneRetry;
+  Label SpinLoop, doneRetry, doRetry;
   addic_(retry_count_Reg, retry_count_Reg, -1);
   blt(CCR0, doneRetry);
 
@@ -2599,16 +2598,26 @@
     mtctr(R0);
   }
 
+  // low thread priority
+  smt_prio_low();
   bind(SpinLoop);
-  smt_yield(); // Can't use waitrsv(). No permission (SIGILL).
 
   if (RTMSpinLoopCount > 1) {
-    bdz(retryLabel);
+    bdz(doRetry);
     ld(R0, 0, owner_addr_Reg);
     cmpdi(CCR0, R0, 0);
     bne(CCR0, SpinLoop);
   }
 
+  bind(doRetry);
+
+  // restore thread priority to default in userspace
+#ifdef LINUX
+  smt_prio_medium_low();
+#else
+  smt_prio_medium();
+#endif
+
   b(retryLabel);
 
   bind(doneRetry);