From 08be8f63c40c030b5cf95b4368e314e563a86301 Mon Sep 17 00:00:00 2001 From: Waiman Long Date: Tue, 31 May 2016 12:53:47 -0400 Subject: [PATCH] locking/pvstat: Separate wait_again and spurious wakeup stats Currently there are overlap in the pvqspinlock wait_again and spurious_wakeup stat counters. Because of lock stealing, it is no longer possible to accurately determine if spurious wakeup has happened in the queue head. As they track both the queue node and queue head status, it is also hard to tell how many of those comes from the queue head and how many from the queue node. This patch changes the accounting rules so that spurious wakeup is only tracked in the queue node. The wait_again count, however, is only tracked in the queue head when the vCPU failed to acquire the lock after a vCPU kick. This should give a much better indication of the wait-kick dynamics in the queue node and the queue head. Signed-off-by: Waiman Long Signed-off-by: Peter Zijlstra (Intel) Cc: Andrew Morton Cc: Boqun Feng Cc: Douglas Hatch Cc: Linus Torvalds Cc: Pan Xinhui Cc: Paul E. McKenney Cc: Peter Zijlstra Cc: Scott J Norton Cc: Thomas Gleixner Link: http://lkml.kernel.org/r/1464713631-1066-2-git-send-email-Waiman.Long@hpe.com Signed-off-by: Ingo Molnar --- kernel/locking/qspinlock_paravirt.h | 12 +++--------- kernel/locking/qspinlock_stat.h | 4 ++-- 2 files changed, 5 insertions(+), 11 deletions(-) diff --git a/kernel/locking/qspinlock_paravirt.h b/kernel/locking/qspinlock_paravirt.h index 429c3dc2a5f3..3acf16d79cf4 100644 --- a/kernel/locking/qspinlock_paravirt.h +++ b/kernel/locking/qspinlock_paravirt.h @@ -288,12 +288,10 @@ static void pv_wait_node(struct mcs_spinlock *node, struct mcs_spinlock *prev) { struct pv_node *pn = (struct pv_node *)node; struct pv_node *pp = (struct pv_node *)prev; - int waitcnt = 0; int loop; bool wait_early; - /* waitcnt processing will be compiled out if !QUEUED_LOCK_STAT */ - for (;; waitcnt++) { + for (;;) { for (wait_early = false, loop = SPIN_THRESHOLD; loop; loop--) { if (READ_ONCE(node->locked)) return; @@ -317,7 +315,6 @@ static void pv_wait_node(struct mcs_spinlock *node, struct mcs_spinlock *prev) if (!READ_ONCE(node->locked)) { qstat_inc(qstat_pv_wait_node, true); - qstat_inc(qstat_pv_wait_again, waitcnt); qstat_inc(qstat_pv_wait_early, wait_early); pv_wait(&pn->state, vcpu_halted); } @@ -458,12 +455,9 @@ pv_wait_head_or_lock(struct qspinlock *lock, struct mcs_spinlock *node) pv_wait(&l->locked, _Q_SLOW_VAL); /* - * The unlocker should have freed the lock before kicking the - * CPU. So if the lock is still not free, it is a spurious - * wakeup or another vCPU has stolen the lock. The current - * vCPU should spin again. + * Because of lock stealing, the queue head vCPU may not be + * able to acquire the lock before it has to wait again. */ - qstat_inc(qstat_pv_spurious_wakeup, READ_ONCE(l->locked)); } /* diff --git a/kernel/locking/qspinlock_stat.h b/kernel/locking/qspinlock_stat.h index b9d031516254..eb0a599fcf58 100644 --- a/kernel/locking/qspinlock_stat.h +++ b/kernel/locking/qspinlock_stat.h @@ -24,8 +24,8 @@ * pv_latency_wake - average latency (ns) from vCPU kick to wakeup * pv_lock_slowpath - # of locking operations via the slowpath * pv_lock_stealing - # of lock stealing operations - * pv_spurious_wakeup - # of spurious wakeups - * pv_wait_again - # of vCPU wait's that happened after a vCPU kick + * pv_spurious_wakeup - # of spurious wakeups in non-head vCPUs + * pv_wait_again - # of wait's after a queue head vCPU kick * pv_wait_early - # of early vCPU wait's * pv_wait_head - # of vCPU wait's at the queue head * pv_wait_node - # of vCPU wait's at a non-head queue node