From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753245AbbGVUNO (ORCPT ); Wed, 22 Jul 2015 16:13:14 -0400 Received: from g4t3427.houston.hp.com ([15.201.208.55]:53047 "EHLO g4t3427.houston.hp.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1750910AbbGVUNL (ORCPT ); Wed, 22 Jul 2015 16:13:11 -0400 From: Waiman Long To: Peter Zijlstra , Ingo Molnar , Thomas Gleixner , "H. Peter Anvin" Cc: x86@kernel.org, linux-kernel@vger.kernel.org, Scott J Norton , Douglas Hatch , Davidlohr Bueso , Waiman Long Subject: [PATCH v3 1/7] locking/pvqspinlock: Unconditional PV kick with _Q_SLOW_VAL Date: Wed, 22 Jul 2015 16:12:36 -0400 Message-Id: <1437595962-21472-2-git-send-email-Waiman.Long@hp.com> X-Mailer: git-send-email 1.7.1 In-Reply-To: <1437595962-21472-1-git-send-email-Waiman.Long@hp.com> References: <1437595962-21472-1-git-send-email-Waiman.Long@hp.com> Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org The smp_store_release() is not a full barrier. In order to avoid missed wakeup, we may need to add memory barrier around locked and cpu state variables adding to complexity. As the chance of spurious wakeup is very low, it is easier and safer to just do an unconditional kick at unlock time. Signed-off-by: Waiman Long --- kernel/locking/qspinlock_paravirt.h | 4 +--- 1 files changed, 1 insertions(+), 3 deletions(-) diff --git a/kernel/locking/qspinlock_paravirt.h b/kernel/locking/qspinlock_paravirt.h index 15d3733..37bc363 100644 --- a/kernel/locking/qspinlock_paravirt.h +++ b/kernel/locking/qspinlock_paravirt.h @@ -240,7 +240,6 @@ static void pv_wait_head(struct qspinlock *lock, struct mcs_spinlock *node) cpu_relax(); } - WRITE_ONCE(pn->state, vcpu_halted); if (!lp) { /* ONCE */ lp = pv_hash(lock, pn); /* @@ -321,8 +320,7 @@ __visible void __pv_queued_spin_unlock(struct qspinlock *lock) * At this point the memory pointed at by lock can be freed/reused, * however we can still use the pv_node to kick the CPU. */ - if (READ_ONCE(node->state) == vcpu_halted) - pv_kick(node->cpu); + pv_kick(node->cpu); } /* * Include the architecture specific callee-save thunk of the -- 1.7.1