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Date: Thu, 09 Apr 2009 19:38:54 +0200
From: Peter Zijlstra <peterz@...radead.org>
To: Heiko Carstens <heiko.carstens@...ibm.com>
Cc: Ingo Molnar <mingo@...e.hu>,
Martin Schwidefsky <schwidefsky@...ibm.com>,
Christian Borntraeger <borntraeger@...ibm.com>,
linux-kernel@...r.kernel.org,
Jeremy Fitzhardinge <jeremy@...p.org>,
Avi Kivity <avi@...hat.com>
Subject: Re: [PATCH] mutex: have non-spinning mutexes on s390 by default
On Thu, 2009-04-09 at 18:53 +0200, Peter Zijlstra wrote:
> I was looking at how an monitor-wait could be used here, but that
> appears non-trivial, there's two variables we're watching, lock->owner
> and rq->curr, either could change.
>
> Reducing that to 1 seems an interesting problem :-)
How about something like this?
Does it make sense to implement an monitor-wait spinlock for the virt
case as well? Avi, Jeremy?
---
arch/Kconfig | 3 +++
arch/x86/Kconfig | 1 +
arch/x86/include/asm/processor.h | 21 +++++++++++++++++++++
include/linux/sched.h | 2 ++
kernel/mutex.h | 1 +
kernel/sched.c | 27 ++++++++++++++++++++++++++-
6 files changed, 54 insertions(+), 1 deletions(-)
diff --git a/arch/Kconfig b/arch/Kconfig
index dc81b34..67aa9f9 100644
--- a/arch/Kconfig
+++ b/arch/Kconfig
@@ -109,3 +109,6 @@ config HAVE_CLK
config HAVE_DMA_API_DEBUG
bool
+
+config HAVE_MUTEX_MWAIT
+ bool
diff --git a/arch/x86/Kconfig b/arch/x86/Kconfig
index 2560fff..62d378b 100644
--- a/arch/x86/Kconfig
+++ b/arch/x86/Kconfig
@@ -47,6 +47,7 @@ config X86
select HAVE_KERNEL_LZMA
select HAVE_ARCH_KMEMCHECK
select HAVE_DMA_API_DEBUG
+ select HAVE_MUTEX_MWAIT
config ARCH_DEFCONFIG
string
diff --git a/arch/x86/include/asm/processor.h b/arch/x86/include/asm/processor.h
index 7c39de7..c2617e4 100644
--- a/arch/x86/include/asm/processor.h
+++ b/arch/x86/include/asm/processor.h
@@ -727,6 +727,27 @@ static inline void __sti_mwait(unsigned long eax, unsigned long ecx)
:: "a" (eax), "c" (ecx));
}
+#ifdef CONFIG_SMP
+static inline void mutex_spin_monitor(void *addr)
+{
+ if (!boot_cpu_has(X86_FEATURE_CLFLUSH_MONITOR))
+ return;
+
+ __monitor(addr, 0, 0);
+ smp_mb();
+}
+
+static inline void mutex_spin_monitor_wait(void)
+{
+ if (!boot_cpu_has(X86_FEATURE_CLFLUSH_MONITOR)) {
+ cpu_relax();
+ return;
+ }
+
+ __mwait(0, 0);
+}
+#endif
+
extern void mwait_idle_with_hints(unsigned long eax, unsigned long ecx);
extern void select_idle_routine(const struct cpuinfo_x86 *c);
diff --git a/include/linux/sched.h b/include/linux/sched.h
index 25bdac7..87f945e 100644
--- a/include/linux/sched.h
+++ b/include/linux/sched.h
@@ -342,7 +342,9 @@ extern signed long schedule_timeout_killable(signed long timeout);
extern signed long schedule_timeout_uninterruptible(signed long timeout);
asmlinkage void __schedule(void);
asmlinkage void schedule(void);
+
extern int mutex_spin_on_owner(struct mutex *lock, struct thread_info *owner);
+extern void mutex_spin_unlock(void);
struct nsproxy;
struct user_namespace;
diff --git a/kernel/mutex.h b/kernel/mutex.h
index 67578ca..c4d2d7a 100644
--- a/kernel/mutex.h
+++ b/kernel/mutex.h
@@ -25,6 +25,7 @@ static inline void mutex_set_owner(struct mutex *lock)
static inline void mutex_clear_owner(struct mutex *lock)
{
lock->owner = NULL;
+ mutex_spin_unlock();
}
#else
static inline void mutex_set_owner(struct mutex *lock)
diff --git a/kernel/sched.c b/kernel/sched.c
index f2cf383..f15af61 100644
--- a/kernel/sched.c
+++ b/kernel/sched.c
@@ -5184,6 +5184,28 @@ need_resched_nonpreemptible:
EXPORT_SYMBOL(schedule);
#ifdef CONFIG_SMP
+
+#ifndef CONFIG_HAVE_MUTEX_MWAIT
+static inline void mutex_spin_monitor(void *addr)
+{
+}
+
+static inline void mutex_spin_monitor_wait(void)
+{
+ cpu_relax();
+}
+#endif
+
+void mutex_spin_unlock(void)
+{
+ /*
+ * XXX fix the below to now require as many ins
+ */
+ preempt_disable();
+ this_rq()->curr = current;
+ preempt_enable();
+}
+
/*
* Look out! "owner" is an entirely speculative pointer
* access and not reliable.
@@ -5225,6 +5247,9 @@ int mutex_spin_on_owner(struct mutex *lock, struct thread_info *owner)
rq = cpu_rq(cpu);
for (;;) {
+
+ mutex_spin_monitor(&rq->curr);
+
/*
* Owner changed, break to re-assess state.
*/
@@ -5237,7 +5262,7 @@ int mutex_spin_on_owner(struct mutex *lock, struct thread_info *owner)
if (task_thread_info(rq->curr) != owner || need_resched())
return 0;
- cpu_relax();
+ mutex_spin_monitor_wait();
}
out:
return 1;
--
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