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Date: Mon, 16 Jun 2014 17:57:14 -0400 From: Waiman Long <waiman.long@...com> To: Peter Zijlstra <a.p.zijlstra@...llo.nl> CC: tglx@...utronix.de, mingo@...nel.org, linux-arch@...r.kernel.org, linux-kernel@...r.kernel.org, virtualization@...ts.linux-foundation.org, xen-devel@...ts.xenproject.org, kvm@...r.kernel.org, paolo.bonzini@...il.com, konrad.wilk@...cle.com, boris.ostrovsky@...cle.com, paulmck@...ux.vnet.ibm.com, riel@...hat.com, torvalds@...ux-foundation.org, raghavendra.kt@...ux.vnet.ibm.com, david.vrabel@...rix.com, oleg@...hat.com, gleb@...hat.com, scott.norton@...com, chegu_vinod@...com, Peter Zijlstra <peterz@...radead.org> Subject: Re: [PATCH 08/11] qspinlock: Revert to test-and-set on hypervisors On 06/15/2014 08:47 AM, Peter Zijlstra wrote: > When we detect a hypervisor (!paravirt, see later patches), revert to > a simple test-and-set lock to avoid the horrors of queue preemption. > > Signed-off-by: Peter Zijlstra<peterz@...radead.org> > --- > arch/x86/include/asm/qspinlock.h | 14 ++++++++++++++ > include/asm-generic/qspinlock.h | 7 +++++++ > kernel/locking/qspinlock.c | 3 +++ > 3 files changed, 24 insertions(+) > > --- a/arch/x86/include/asm/qspinlock.h > +++ b/arch/x86/include/asm/qspinlock.h > @@ -1,6 +1,7 @@ > #ifndef _ASM_X86_QSPINLOCK_H > #define _ASM_X86_QSPINLOCK_H > > +#include<asm/cpufeature.h> > #include<asm-generic/qspinlock_types.h> > > #if !defined(CONFIG_X86_OOSTORE)&& !defined(CONFIG_X86_PPRO_FENCE) > @@ -20,6 +21,19 @@ static inline void queue_spin_unlock(str > > #endif /* !CONFIG_X86_OOSTORE&& !CONFIG_X86_PPRO_FENCE */ > > +#define virt_queue_spin_lock virt_queue_spin_lock > + > +static inline bool virt_queue_spin_lock(struct qspinlock *lock) > +{ > + if (!static_cpu_has(X86_FEATURE_HYPERVISOR)) > + return false; > + > + while (atomic_cmpxchg(&lock->val, 0, _Q_LOCKED_VAL) != 0) > + cpu_relax(); > + > + return true; > +} > + > #include<asm-generic/qspinlock.h> > > #endif /* _ASM_X86_QSPINLOCK_H */ > --- a/include/asm-generic/qspinlock.h > +++ b/include/asm-generic/qspinlock.h > @@ -98,6 +98,13 @@ static __always_inline void queue_spin_u > } > #endif > > +#ifndef virt_queue_spin_lock > +static __always_inline bool virt_queue_spin_lock(struct qspinlock *lock) > +{ > + return false; > +} > +#endif > + > /* > * Initializier > */ > --- a/kernel/locking/qspinlock.c > +++ b/kernel/locking/qspinlock.c > @@ -247,6 +247,9 @@ void queue_spin_lock_slowpath(struct qsp > > BUILD_BUG_ON(CONFIG_NR_CPUS>= (1U<< _Q_TAIL_CPU_BITS)); > > + if (virt_queue_spin_lock(lock)) > + return; > + > /* > * wait for in-progress pending->locked hand-overs > * I just wonder if it is better to allow the kernel distributors to decide if unfair lock should be the default for virtual guest. Anyway, I have no objection to that myself. -Longman -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@...r.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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