From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752062AbcFZGms (ORCPT ); Sun, 26 Jun 2016 02:42:48 -0400 Received: from mx0a-001b2d01.pphosted.com ([148.163.156.1]:16530 "EHLO mx0a-001b2d01.pphosted.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751892AbcFZGmc (ORCPT ); Sun, 26 Jun 2016 02:42:32 -0400 X-IBM-Helo: d03dlp02.boulder.ibm.com X-IBM-MailFrom: xinhui.pan@linux.vnet.ibm.com From: Pan Xinhui To: linux-kernel@vger.kernel.org Cc: peterz@infradead.org, mingo@redhat.com, boqun.feng@gmail.com, Pan Xinhui Subject: [PATCH 2/2] locking/osq: Drop the overload of osq_lock() Date: Sun, 26 Jun 2016 06:41:55 -0400 X-Mailer: git-send-email 2.4.11 In-Reply-To: <1466937715-6683-1-git-send-email-xinhui.pan@linux.vnet.ibm.com> References: <1466937715-6683-1-git-send-email-xinhui.pan@linux.vnet.ibm.com> X-TM-AS-GCONF: 00 X-Content-Scanned: Fidelis XPS MAILER x-cbid: 16062606-0028-0000-0000-0000050A1AE6 X-IBM-AV-DETECTION: SAVI=unused REMOTE=unused XFE=unused x-cbparentid: 16062606-0029-0000-0000-00002CFEECEC Message-Id: <1466937715-6683-3-git-send-email-xinhui.pan@linux.vnet.ibm.com> X-Proofpoint-Virus-Version: vendor=fsecure engine=2.50.10432:,, definitions=2016-06-26_04:,, signatures=0 X-Proofpoint-Spam-Details: rule=outbound_notspam policy=outbound score=0 spamscore=0 suspectscore=1 malwarescore=0 phishscore=0 adultscore=0 bulkscore=0 classifier=spam adjust=0 reason=mlx scancount=1 engine=8.0.1-1604210000 definitions=main-1606260074 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org An over-committed guest with more vCPUs than pCPUs has a heavy overload in osq_lock(). This is because vCPU A hold the osq lock and yield out, vCPU B wait per_cpu node->locked to be set. IOW, vCPU B wait vCPU A to run and unlock the osq lock. So lets also use neet_yield_to() to detect if we need stop the spinning Signed-off-by: Pan Xinhui --- kernel/locking/osq_lock.c | 18 +++++++++++++++--- 1 file changed, 15 insertions(+), 3 deletions(-) diff --git a/kernel/locking/osq_lock.c b/kernel/locking/osq_lock.c index 05a3785..4287603 100644 --- a/kernel/locking/osq_lock.c +++ b/kernel/locking/osq_lock.c @@ -21,6 +21,11 @@ static inline int encode_cpu(int cpu_nr) return cpu_nr + 1; } +static inline int node_cpu(struct optimistic_spin_node *node) +{ + return node->cpu - 1; +} + static inline struct optimistic_spin_node *decode_cpu(int encoded_cpu_val) { int cpu_nr = encoded_cpu_val - 1; @@ -84,9 +89,10 @@ osq_wait_next(struct optimistic_spin_queue *lock, bool osq_lock(struct optimistic_spin_queue *lock) { struct optimistic_spin_node *node = this_cpu_ptr(&osq_node); - struct optimistic_spin_node *prev, *next; + struct optimistic_spin_node *prev, *next, *prev_old; int curr = encode_cpu(smp_processor_id()); int old; + unsigned int yield_count; node->locked = 0; node->next = NULL; @@ -114,14 +120,20 @@ bool osq_lock(struct optimistic_spin_queue *lock) * guaranteed their existence -- this allows us to apply * cmpxchg in an attempt to undo our queueing. */ - + prev_old = prev; + yield_count = vcpu_get_yield_count(node_cpu(prev)); while (!READ_ONCE(node->locked)) { /* * If we need to reschedule bail... so we can block. */ - if (need_resched()) + if (need_resched() || + need_yield_to(node_cpu(prev), yield_count)) goto unqueue; + prev = READ_ONCE(node->prev); + if (prev != prev_old) + yield_count = vcpu_get_yield_count(node_cpu(prev)); + cpu_relax_lowlatency(); } return true; -- 2.4.11