code review 4711045: runtime: improve Linux mutex

src/pkg/runtime/386/asm.s

 // Copyright 2009 The Go Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style
 // license that can be found in the LICENSE file.
 
 #include "386/asm.h"
 
 TEXT _rt0_386(SB),7,$0
         // Linux, Windows start the FPU in extended double precision.
         // Other operating systems use double precision.
         // Change to double precision to match them,
@@ skipping 313 matching lines @@
 //      return *val;
 TEXT runtime·xadd(SB), 7, $0
         MOVL    4(SP), BX
         MOVL    8(SP), AX
         MOVL    AX, CX
         LOCK
         XADDL   AX, 0(BX)
         ADDL    CX, AX
         RET
 
+TEXT runtime·xchg(SB), 7, $0
+        MOVL    4(SP), BX
+        MOVL    8(SP), AX
+        XCHGL   AX, 0(BX)
+        RET
+
+TEXT runtime·procyield(SB),7,$0
+        MOVL    4(SP), AX
+again:
+        PAUSE
+        SUBL    $1, AX
+        JNZ     again
+        RET
+
 TEXT runtime·atomicstorep(SB), 7, $0
         MOVL    4(SP), BX
         MOVL    8(SP), AX
         XCHGL   AX, 0(BX)
         RET
 
 // void jmpdefer(fn, sp);
 // called from deferreturn.
 // 1. pop the caller
 // 2. sub 5 bytes from the callers return
@@ skipping 173 matching lines @@
         CALL    runtime·setldt(SB)
         RET
 
 TEXT runtime·emptyfunc(SB),0,$0
         RET
 
 TEXT runtime·abort(SB),7,$0
         INT $0x3
 
 GLOBL runtime·tls0(SB), $32