Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S932414AbaFPV5W (ORCPT ); Mon, 16 Jun 2014 17:57:22 -0400 Received: from g4t3425.houston.hp.com ([15.201.208.53]:6317 "EHLO g4t3425.houston.hp.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1754764AbaFPV5U (ORCPT ); Mon, 16 Jun 2014 17:57:20 -0400 Message-ID: <539F683A.2070103@hp.com> Date: Mon, 16 Jun 2014 17:57:14 -0400 From: Waiman Long User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:10.0.12) Gecko/20130109 Thunderbird/10.0.12 MIME-Version: 1.0 To: Peter Zijlstra CC: tglx@linutronix.de, mingo@kernel.org, linux-arch@vger.kernel.org, linux-kernel@vger.kernel.org, virtualization@lists.linux-foundation.org, xen-devel@lists.xenproject.org, kvm@vger.kernel.org, paolo.bonzini@gmail.com, konrad.wilk@oracle.com, boris.ostrovsky@oracle.com, paulmck@linux.vnet.ibm.com, riel@redhat.com, torvalds@linux-foundation.org, raghavendra.kt@linux.vnet.ibm.com, david.vrabel@citrix.com, oleg@redhat.com, gleb@redhat.com, scott.norton@hp.com, chegu_vinod@hp.com, Peter Zijlstra Subject: Re: [PATCH 08/11] qspinlock: Revert to test-and-set on hypervisors References: <20140615124657.264658593@chello.nl> <20140615130153.940699466@chello.nl> In-Reply-To: <20140615130153.940699466@chello.nl> Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org 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 > --- > 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 > #include > > #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 > > #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@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/