Messages in this thread | | | Date | Wed, 30 Jun 2010 12:08:46 +0200 | From | Jeremy Fitzhardinge <> | Subject | Re: [PATCH 4/4, v2] x86: enlightenment for ticket spin locks - improve yield behavior on Xen |
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On 06/29/2010 04:35 PM, Jan Beulich wrote: > 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@novell.com> > Cc: Jeremy Fitzhardinge <jeremy.fitzhardinge@citrix.com> > Cc: KY Srinivasan <ksrinivasan@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); >
Why not smp_processor_id()? Is this different in some way?
> +#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. > > > >
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