From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1751021AbcGNIQH (ORCPT ); Thu, 14 Jul 2016 04:16:07 -0400 Received: from mail-pf0-f194.google.com ([209.85.192.194]:35726 "EHLO mail-pf0-f194.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1750947AbcGNIQB (ORCPT ); Thu, 14 Jul 2016 04:16:01 -0400 From: Wanpeng Li X-Google-Original-From: Wanpeng Li To: linux-kernel@vger.kernel.org Cc: Wanpeng Li , "Peter Zijlstra (Intel)" , Ingo Molnar , Waiman Long , Davidlohr Bueso Subject: [PATCH v2] locking/pvqspinlock: restore/set vcpu_hashed state after failing adaptive locking spinning Date: Thu, 14 Jul 2016 16:15:56 +0800 Message-Id: <1468484156-4521-1-git-send-email-wanpeng.li@hotmail.com> X-Mailer: git-send-email 1.9.1 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org From: Wanpeng Li When the lock holder vCPU is racing with the queue head: CPU 0 (lock holder) CPU1 (queue head) =================== ================= spin_lock(); spin_lock(); pv_kick_node(): pv_wait_head_or_lock(): if (!lp) { lp = pv_hash(lock, pn); xchg(&l->locked, _Q_SLOW_VAL); } WRITE_ONCE(pn->state, vcpu_halted); cmpxchg(&pn->state, vcpu_halted, vcpu_hashed); WRITE_ONCE(l->locked, _Q_SLOW_VAL); (void)pv_hash(lock, pn); In this case, lock holder inserts the pv_node of queue head into the hash table and set _Q_SLOW_VAL unnecessary. This patch avoids it by restoring/setting vcpu_halted state after failing adaptive locking spinning. Cc: Peter Zijlstra (Intel) Cc: Ingo Molnar Cc: Waiman Long Cc: Davidlohr Bueso Signed-off-by: Wanpeng Li --- v1 -> v2: * adjust patch description kernel/locking/qspinlock_paravirt.h | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) diff --git a/kernel/locking/qspinlock_paravirt.h b/kernel/locking/qspinlock_paravirt.h index 21ede57..ac7d20b 100644 --- a/kernel/locking/qspinlock_paravirt.h +++ b/kernel/locking/qspinlock_paravirt.h @@ -450,7 +450,7 @@ pv_wait_head_or_lock(struct qspinlock *lock, struct mcs_spinlock *node) goto gotlock; } } - WRITE_ONCE(pn->state, vcpu_halted); + WRITE_ONCE(pn->state, vcpu_hashed); qstat_inc(qstat_pv_wait_head, true); qstat_inc(qstat_pv_wait_again, waitcnt); pv_wait(&l->locked, _Q_SLOW_VAL); -- 1.9.1