Messages in this thread | | | Date | Tue, 29 Jun 2010 18:13:02 -0700 | From | "H. Peter Anvin" <> | Subject | Re: [PATCH 3/4, v2] x86: enlightenment for ticket spin locks - eliminate NOPs introduced by first patch |
| |
On 06/29/2010 07:33 AM, Jan Beulich wrote: > 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. > > --- 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"
If you're stretching (bloating) them anyway, perhaps we should be using "add" instructions instead, with their better EFLAGS behavior?
-hpa
| |