lkml.org 
[lkml]   [2015]   [Mar]   [16]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
Patch in this message
/
Date
From
Subject[PATCH 7/9] qspinlock: Revert to test-and-set on hypervisors
From: Peter Zijlstra <peterz@infradead.org>

When we detect a hypervisor (!paravirt, see qspinlock paravirt support
patches), revert to a simple test-and-set lock to avoid the horrors
of queue preemption.

Cc: Ingo Molnar <mingo@redhat.com>
Cc: David Vrabel <david.vrabel@citrix.com>
Cc: Oleg Nesterov <oleg@redhat.com>
Cc: Scott J Norton <scott.norton@hp.com>
Cc: Paolo Bonzini <paolo.bonzini@gmail.com>
Cc: Douglas Hatch <doug.hatch@hp.com>
Cc: Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>
Cc: Boris Ostrovsky <boris.ostrovsky@oracle.com>
Cc: "Paul E. McKenney" <paulmck@linux.vnet.ibm.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: "H. Peter Anvin" <hpa@zytor.com>
Cc: Rik van Riel <riel@redhat.com>
Cc: Raghavendra K T <raghavendra.kt@linux.vnet.ibm.com>
Signed-off-by: Waiman Long <Waiman.Long@hp.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Link: http://lkml.kernel.org/r/1421784755-21945-8-git-send-email-Waiman.Long@hp.com
---
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>

#define queue_spin_unlock queue_spin_unlock
@@ -15,6 +16,19 @@ static inline void queue_spin_unlock(str
smp_store_release((u8 *)lock, 0);
}

+#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
@@ -111,6 +111,13 @@ static inline void queue_spin_unlock_wai
cpu_relax();
}

+#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
@@ -259,6 +259,9 @@ 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
*



\
 
 \ /
  Last update: 2015-03-16 15:01    [from the cache]
©2003-2020 Jasper Spaans|hosted at Digital Ocean and my Meterkast|Read the blog