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From: Peter Zijlstra <peterz@infradead.org>
To: Yi Sun <yi.y.sun@linux.intel.com>
Cc: Waiman Long <longman@redhat.com>, Juergen Gross <jgross@suse.com>,
	linux-kernel@vger.kernel.org, x86@kernel.org, tglx@linutronix.de,
	chao.p.peng@intel.com, chao.gao@intel.com,
	isaku.yamahata@intel.com, michael.h.kelley@microsoft.com,
	tianyu.lan@microsoft.com, "K. Y. Srinivasan" <kys@microsoft.com>,
	Haiyang Zhang <haiyangz@microsoft.com>,
	Stephen Hemminger <sthemmin@microsoft.com>,
	"mingo@redhat.com" <mingo@redhat.com>,
	Will Deacon <will.deacon@arm.com>
Subject: Re: [PATCH v1 2/2] x86/hyperv: make HvNotifyLongSpinWait hypercall
Date: Wed, 31 Oct 2018 15:10:30 +0100	[thread overview]
Message-ID: <20181031141030.GB13219@hirez.programming.kicks-ass.net> (raw)
In-Reply-To: <20181031015417.GC15378@yi.y.sun>

On Wed, Oct 31, 2018 at 09:54:17AM +0800, Yi Sun wrote:
> On 18-10-23 17:33:28, Yi Sun wrote:
> > On 18-10-23 10:51:27, Peter Zijlstra wrote:

> > > Can you try and explain why vcpu_is_preempted() doesn't work for you?
> > 
> > I thought HvSpinWaitInfo is used to notify hypervisor the spin number
> > which is different with vcpu_is_preempted. So I did not consider
> > vcpu_is_preempted.
> > 
> > But HvSpinWaitInfo is a quite simple function and could be combined
> > with vcpu_is_preempted together. So I think it is OK to use
> > vcpu_is_preempted to make codes clean. I will have a try.
> 
> After checking codes, there is one issue to call vcpu_is_preempted.
> There are two spin loops in qspinlock_paravirt.h. One loop in
> 'pv_wait_node' calls vcpu_is_preempted. But another loop in
> 'pv_wait_head_or_lock' does not call vcpu_is_preempted. It also does
> not call any other ops of 'pv_lock_ops' in the loop. So I am afraid
> we have to add one more ops in 'pv_lock_ops' to do this.

Why? Would not something like the below cure that? Waiman, can you have
a look at this; I always forget how that paravirt crud works.

---
 kernel/locking/qspinlock.c          | 5 +++--
 kernel/locking/qspinlock_paravirt.h | 5 +++--
 2 files changed, 6 insertions(+), 4 deletions(-)

diff --git a/kernel/locking/qspinlock.c b/kernel/locking/qspinlock.c
index 8a8c3c208c5e..a4ab80f95176 100644
--- a/kernel/locking/qspinlock.c
+++ b/kernel/locking/qspinlock.c
@@ -286,7 +286,8 @@ static __always_inline void __pv_wait_node(struct mcs_spinlock *node,
 static __always_inline void __pv_kick_node(struct qspinlock *lock,
 					   struct mcs_spinlock *node) { }
 static __always_inline u32  __pv_wait_head_or_lock(struct qspinlock *lock,
-						   struct mcs_spinlock *node)
+						   struct mcs_spinlock *node,
+						   struct mcs_spinlock *prev)
 						   { return 0; }
 
 #define pv_enabled()		false
@@ -500,7 +501,7 @@ void queued_spin_lock_slowpath(struct qspinlock *lock, u32 val)
 	 * If PV isn't active, 0 will be returned instead.
 	 *
 	 */
-	if ((val = pv_wait_head_or_lock(lock, node)))
+	if ((val = pv_wait_head_or_lock(lock, node, prev)))
 		goto locked;
 
 	val = atomic_cond_read_acquire(&lock->val, !(VAL & _Q_LOCKED_PENDING_MASK));
diff --git a/kernel/locking/qspinlock_paravirt.h b/kernel/locking/qspinlock_paravirt.h
index 0130e488ebfe..531dadc955fb 100644
--- a/kernel/locking/qspinlock_paravirt.h
+++ b/kernel/locking/qspinlock_paravirt.h
@@ -399,9 +399,10 @@ static void pv_kick_node(struct qspinlock *lock, struct mcs_spinlock *node)
  * The current value of the lock will be returned for additional processing.
  */
 static u32
-pv_wait_head_or_lock(struct qspinlock *lock, struct mcs_spinlock *node)
+pv_wait_head_or_lock(struct qspinlock *lock, struct mcs_spinlock *node, struct mcs_spinlock *prev)
 {
 	struct pv_node *pn = (struct pv_node *)node;
+	struct pv_node *pp = (struct pv_node *)prev;
 	struct qspinlock **lp = NULL;
 	int waitcnt = 0;
 	int loop;
@@ -430,7 +431,7 @@ pv_wait_head_or_lock(struct qspinlock *lock, struct mcs_spinlock *node)
 		 * disable lock stealing before attempting to acquire the lock.
 		 */
 		set_pending(lock);
-		for (loop = SPIN_THRESHOLD; loop; loop--) {
+		for (loop = SPIN_THRESHOLD; loop && !vcpu_is_preempted(prev->cpu); loop--) {
 			if (trylock_clear_pending(lock))
 				goto gotlock;
 			cpu_relax();


  reply	other threads:[~2018-10-31 14:11 UTC|newest]

Thread overview: 25+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2018-10-19 13:13 [PATCH v1 0/2] Enable HvNotifyLongSpinWait for Hyper-V Yi Sun
2018-10-19 13:13 ` [PATCH v1 1/2] x86/hyperv: get spinlock retry number on Hyper-V Yi Sun
2018-10-19 13:13 ` [PATCH v1 2/2] x86/hyperv: make HvNotifyLongSpinWait hypercall Yi Sun
2018-10-19 14:20   ` Juergen Gross
2018-10-22  1:53     ` Yi Sun
2018-10-22  7:32       ` Juergen Gross
2018-10-22 16:31         ` Waiman Long
2018-10-22 17:15           ` Peter Zijlstra
2018-10-22 17:27             ` Waiman Long
2018-10-22 17:31               ` Peter Zijlstra
2018-10-22 18:01                 ` Waiman Long
2018-10-23  2:57             ` Yi Sun
2018-10-23  8:51               ` Peter Zijlstra
2018-10-23  9:33                 ` Yi Sun
2018-10-31  1:54                   ` Yi Sun
2018-10-31 14:10                     ` Peter Zijlstra [this message]
2018-10-31 15:07                       ` Waiman Long
2018-10-31 17:15                         ` Peter Zijlstra
2018-11-01  3:20                           ` Yi Sun
2018-11-01  8:59                             ` Peter Zijlstra
2018-11-01 12:59                             ` Waiman Long
2018-11-05  6:54                               ` Yi Sun
2018-10-24 16:53   ` Michael Kelley
2018-10-25  2:23     ` Yi Sun
2018-10-31  2:06     ` Yi Sun

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