[PATCH 4/4, v2] x86: enlightenment for ticket spin locks - improve yield behavior on Xen
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From: Jan Beulich on 29 Jun 2010 10:40 This optional patch improves yielding behavior in that the acquire function now checks whether the vCPU owning the lock is actually running, yielding immediately if it isn't. The (only) additional overhead this introduces for native execution is the writing of the owning CPU in the lock acquire paths. If this is considered a problem but the patch otherwise is deemed useful, even that code could be eliminated for native execution (by further alternative instruction patching). 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/include/asm/spinlock.h | 13 +++++++++++++ arch/x86/include/asm/spinlock_types.h | 5 +++++ arch/x86/kernel/cpu/xen.c | 5 ++++- 3 files changed, 22 insertions(+), 1 deletion(-) --- 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 @@ -85,6 +85,15 @@ extern void virt_spin_unlock_stub(void); # define UNLOCK_LOCK_PREFIX #endif +static __always_inline void __ticket_spin_set_owner(arch_spinlock_t *lock, + int owned) +{ +#ifdef CONFIG_ENLIGHTEN_SPINLOCKS + if (owned) + lock->owner = percpu_read(cpu_number); +#endif +} + /* * Ticket locks are conceptually two parts, one indicating the current head of * the queue, and the other indicating the current tail. The lock is acquired @@ -124,6 +133,7 @@ static __always_inline void __ticket_spi ASM_OUTPUT2("+Q" (inc), "+m" (lock->slock)), [stub] "i" (virt_spin_lock_stub) : "memory", "cc"); + __ticket_spin_set_owner(lock, true); } static __always_inline int __ticket_spin_trylock(arch_spinlock_t *lock) @@ -141,6 +151,7 @@ static __always_inline int __ticket_spin : "=&a" (tmp), "=&q" (new), "+m" (lock->slock) : : "memory", "cc"); + __ticket_spin_set_owner(lock, tmp); return tmp; } @@ -192,6 +203,7 @@ static __always_inline void __ticket_spi ASM_OUTPUT2("+r" (inc), "+m" (lock->slock), "=&r" (tmp)), [stub] "i" (virt_spin_lock_stub) : "memory", "cc"); + __ticket_spin_set_owner(lock, true); } static __always_inline int __ticket_spin_trylock(arch_spinlock_t *lock) @@ -212,6 +224,7 @@ static __always_inline int __ticket_spin : "=&a" (tmp), "=&q" (new), "+m" (lock->slock) : : "memory", "cc"); + __ticket_spin_set_owner(lock, tmp); return tmp; } --- 2.6.35-rc3-virt-spinlocks.orig/arch/x86/include/asm/spinlock_types.h +++ 2.6.35-rc3-virt-spinlocks/arch/x86/include/asm/spinlock_types.h @@ -17,6 +17,11 @@ typedef struct arch_spinlock { # else u16 cur, seq; # endif +# if CONFIG_NR_CPUS <= 256 + u8 owner; +# else + u16 owner; +# endif }; #endif }; --- 2.6.35-rc3-virt-spinlocks.orig/arch/x86/kernel/cpu/xen.c +++ 2.6.35-rc3-virt-spinlocks/arch/x86/kernel/cpu/xen.c @@ -79,7 +79,8 @@ static void xen_spin_lock(struct arch_sp for (count = spin_count; ({ barrier(); lock->cur != token; }); ) if (likely(cpu_online(raw_smp_processor_id())) - && unlikely(!--count)) { + && (per_cpu(runstate.state, lock->owner) != RUNSTATE_running + || unlikely(!--count))) { struct sched_poll sched_poll; set_xen_guest_handle(sched_poll.ports, @@ -91,6 +92,8 @@ static void xen_spin_lock(struct arch_sp } else cpu_relax(); + lock->owner = raw_smp_processor_id(); + /* * If we interrupted another spinlock while it was blocking, make * sure it doesn't block (again) without re-checking the lock. -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo(a)vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/ |