Prev: [PATCH 4/4, v2] x86: enlightenment for ticket spin locks - improve yield behavior on Xen
Next: [PATCH 2/4, v2] x86: enlightenment for ticket spin locks - Xen implementation
From: Jan Beulich on 29 Jun 2010 10:40
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(a)novell.com>
Cc: Jeremy Fitzhardinge <jeremy.fitzhardinge(a)citrix.com>
Cc: KY Srinivasan <ksrinivasan(a)novell.com>

---
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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Prev: [PATCH 4/4, v2] x86: enlightenment for ticket spin locks - improve yield behavior on Xen
Next: [PATCH 2/4, v2] x86: enlightenment for ticket spin locks - Xen implementation