[PATCH 3/4, v2] x86: enlightenment for ticket spin locks - eliminate NOPs introduced by first patch

[Jan Beulich]

Under the assumption that the nop-s added by the base ticket spinlock
enlightenment patch might be considered undesirable (or worse), here
is an optional patch to eliminate these nop-s again. This is done
through extending the memory operands of the inc instructions used for
unlocking ticket locks to the necessary size, using assembler and
linker features.

Signed-off-by: Jan Beulich <jbeulich@xxxxxxxxxx>
Cc: Jeremy Fitzhardinge <jeremy.fitzhardinge@xxxxxxxxxx>
Cc: KY Srinivasan <ksrinivasan@xxxxxxxxxx>

---
 arch/x86/Makefile                      |    3 +
 arch/x86/include/asm/alternative-asm.h |   59 +++++++++++++++++++++++++++++++++
 arch/x86/include/asm/alternative.h     |    5 ++
 arch/x86/include/asm/spinlock.h        |    7 +--
 arch/x86/kernel/symdefs.lds            |    1 
 arch/x86/kernel/vmlinux.lds.S          |    2 +
 6 files changed, 72 insertions(+), 5 deletions(-)

--- 2.6.35-rc3-virt-spinlocks.orig/arch/x86/Makefile
+++ 2.6.35-rc3-virt-spinlocks/arch/x86/Makefile
@@ -87,6 +87,9 @@ ifeq ($(CONFIG_KMEMCHECK),y)
 	KBUILD_CFLAGS += $(call cc-option,-fno-builtin-memcpy)
 endif
 
+KBUILD_CFLAGS += -Wa,-I$(srctree)/arch/x86/include
+LDFLAGS_MODULE += -T $(srctree)/arch/x86/kernel/symdefs.lds
+
 # Stackpointer is addressed different for 32 bit and 64 bit x86
 sp-$(CONFIG_X86_32) := esp
 sp-$(CONFIG_X86_64) := rsp
--- 2.6.35-rc3-virt-spinlocks.orig/arch/x86/include/asm/alternative.h
+++ 2.6.35-rc3-virt-spinlocks/arch/x86/include/asm/alternative.h
@@ -6,6 +6,11 @@
 #include <linux/stringify.h>
 #include <asm/asm.h>
 
+#if !defined(__ASSEMBLY__) && !defined(__PIC__)
+#include <asm/alternative-asm.h> /* just for tracking the build dependency */
+__asm__(".include \"asm/alternative-asm.h\"");
+#endif
+
 /*
  * Alternative inline assembly for SMP.
  *
--- 2.6.35-rc3-virt-spinlocks.orig/arch/x86/include/asm/alternative-asm.h
+++ 2.6.35-rc3-virt-spinlocks/arch/x86/include/asm/alternative-asm.h
@@ -1,3 +1,7 @@
+#if 0 /* Hide this from compiler. */
+	.if 0 # Hide assembly source stuff when assembling compiler output.
+#endif
+
 #ifdef __ASSEMBLY__
 
 #include <asm/asm.h>
@@ -16,3 +20,58 @@
 #endif
 
 #endif  /*  __ASSEMBLY__  */
+
+#if 0 /* Hide this from compiler. */
+	.else # Code to be used in compiler output:
+
+	.weak _$.zero
+
+	.macro unary opc arg1 arg2 arg3
+	 .Lempty=2
+	 .irpc c,"\arg2"
+	  .Lempty=3
+	 .endr
+	 .irpc c,"\arg3"
+	  .Lempty=0
+	 .endr
+	 .Lsym=1
+	 .Lnum=0
+	 .irpc c,"\arg1"
+	  .irpc m,"(123456789-0"
+	   .ifeqs "\c","\m"
+	    .Lsym=0
+	    .exitm
+	   .endif
+	   .Lnum=1
+	  .endr
+	  .exitm
+	 .endr
+	 .if .Lempty == 2
+	  .if .Lsym
+	   \opc \arg1
+	  .elseif .Lnum
+	   \opc _$.zero+\arg1
+	  .else
+	   \opc _$.zero\arg1
+	  .endif
+	 .elseif .Lempty == 3
+	  .if .Lsym
+	   \opc \arg1,\arg2
+	  .elseif .Lnum
+	   \opc _$.zero+\arg1,\arg2
+	  .else
+	   \opc _$.zero\arg1,\arg2
+	  .endif
+	 .else
+	  .if .Lsym
+	   \opc \arg1,\arg2,\arg3
+	  .elseif .Lnum
+	   \opc _$.zero+\arg1,\arg2,\arg3
+	  .else
+	   \opc _$.zero\arg1,\arg2,\arg3
+	  .endif
+	 .endif
+	.endm
+
+	.endif
+#endif
--- 2.6.35-rc3-virt-spinlocks.orig/arch/x86/include/asm/spinlock.h
+++ 2.6.35-rc3-virt-spinlocks/arch/x86/include/asm/spinlock.h
@@ -10,7 +10,6 @@
 
 #ifdef CONFIG_ENLIGHTEN_SPINLOCKS
 #include <asm/alternative.h>
-#include <asm/nops.h>
 /* Including asm/smp.h here causes a cyclic include dependency. */
 #include <asm/percpu.h>
 DECLARE_PER_CPU(int, cpu_number);
@@ -156,8 +155,7 @@ static __always_inline void __ticket_spi
 #else
 	unsigned int token;
 
-	alternative_io(UNLOCK_LOCK_PREFIX "incb %[lock]\n\t"
-		ASM_NOP3,
+	alternative_io(UNLOCK_LOCK_PREFIX "unary incb %[lock]\n\t",
 		ALTERNATIVE_TICKET_UNLOCK_HEAD
 		UNLOCK_LOCK_PREFIX "incb %[lock]\n\t"
 		"movzwl %[lock], %[token]\n\t"
@@ -228,8 +226,7 @@ static __always_inline void __ticket_spi
 #else
 	unsigned int token, tmp;
 
-	alternative_io(UNLOCK_LOCK_PREFIX "incw %[lock]\n\t"
-		ASM_NOP2,
+	alternative_io(UNLOCK_LOCK_PREFIX "unary incw %[lock]\n\t",
 		ALTERNATIVE_TICKET_UNLOCK_HEAD
 		UNLOCK_LOCK_PREFIX "incw %[lock]\n\t"
 		"movl %[lock], %[token]\n\t"
--- /dev/null
+++ 2.6.35-rc3-virt-spinlocks/arch/x86/kernel/symdefs.lds
@@ -0,0 +1 @@
+_$.zero = 0;
--- 2.6.35-rc3-virt-spinlocks.orig/arch/x86/kernel/vmlinux.lds.S
+++ 2.6.35-rc3-virt-spinlocks/arch/x86/kernel/vmlinux.lds.S
@@ -27,6 +27,8 @@
 #include <asm/cache.h>
 #include <asm/boot.h>
 
+#include "symdefs.lds"
+
 #undef i386     /* in case the preprocessor is a 32bit one */
 
 OUTPUT_FORMAT(CONFIG_OUTPUT_FORMAT, CONFIG_OUTPUT_FORMAT, CONFIG_OUTPUT_FORMAT)


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