Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1757197AbcJSGYH (ORCPT ); Wed, 19 Oct 2016 02:24:07 -0400 Received: from mx0b-001b2d01.pphosted.com ([148.163.158.5]:42530 "EHLO mx0a-001b2d01.pphosted.com" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S1756442AbcJSGW6 (ORCPT ); Wed, 19 Oct 2016 02:22:58 -0400 From: Pan Xinhui To: linux-kernel@vger.kernel.org, linuxppc-dev@lists.ozlabs.org, virtualization@lists.linux-foundation.org, linux-s390@vger.kernel.org, xen-devel-request@lists.xenproject.org, kvm@vger.kernel.org Cc: benh@kernel.crashing.org, paulus@samba.org, mpe@ellerman.id.au, mingo@redhat.com, peterz@infradead.org, paulmck@linux.vnet.ibm.com, will.deacon@arm.com, kernellwp@gmail.com, jgross@suse.com, pbonzini@redhat.com, bsingharora@gmail.com, boqun.feng@gmail.com, borntraeger@de.ibm.com, Pan Xinhui Subject: [PATCH v4 3/5] kernel/locking: Drop the overload of {mutex,rwsem}_spin_on_owner Date: Wed, 19 Oct 2016 06:20:14 -0400 X-Mailer: git-send-email 2.4.11 In-Reply-To: <1476872416-42752-1-git-send-email-xinhui.pan@linux.vnet.ibm.com> References: <1476872416-42752-1-git-send-email-xinhui.pan@linux.vnet.ibm.com> X-TM-AS-GCONF: 00 X-Content-Scanned: Fidelis XPS MAILER x-cbid: 16101906-0004-0000-0000-000010A44BBD X-IBM-SpamModules-Scores: X-IBM-SpamModules-Versions: BY=3.00005938; HX=3.00000240; KW=3.00000007; PH=3.00000004; SC=3.00000187; SDB=6.00770084; UDB=6.00369057; IPR=6.00546549; BA=6.00004818; NDR=6.00000001; ZLA=6.00000005; ZF=6.00000009; ZB=6.00000000; ZP=6.00000000; ZH=6.00000000; ZU=6.00000002; MB=3.00013038; XFM=3.00000011; UTC=2016-10-19 06:22:54 X-IBM-AV-DETECTION: SAVI=unused REMOTE=unused XFE=unused x-cbparentid: 16101906-0005-0000-0000-000079DACA5B Message-Id: <1476872416-42752-4-git-send-email-xinhui.pan@linux.vnet.ibm.com> X-Proofpoint-Virus-Version: vendor=fsecure engine=2.50.10432:,, definitions=2016-10-19_02:,, signatures=0 X-Proofpoint-Spam-Details: rule=outbound_notspam policy=outbound score=0 spamscore=0 suspectscore=0 malwarescore=0 phishscore=0 adultscore=0 bulkscore=0 classifier=spam adjust=0 reason=mlx scancount=1 engine=8.0.1-1609300000 definitions=main-1610190114 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 3703 Lines: 103 An over-committed guest with more vCPUs than pCPUs has a heavy overload in the two spin_on_owner. This blames on the lock holder preemption issue. Kernel has an interface bool vcpu_is_preempted(int cpu) to see if a vCPU is currently running or not. So break the spin loops on true condition. test-case: perf record -a perf bench sched messaging -g 400 -p && perf report before patch: 20.68% sched-messaging [kernel.vmlinux] [k] mutex_spin_on_owner 8.45% sched-messaging [kernel.vmlinux] [k] mutex_unlock 4.12% sched-messaging [kernel.vmlinux] [k] system_call 3.01% sched-messaging [kernel.vmlinux] [k] system_call_common 2.83% sched-messaging [kernel.vmlinux] [k] copypage_power7 2.64% sched-messaging [kernel.vmlinux] [k] rwsem_spin_on_owner 2.00% sched-messaging [kernel.vmlinux] [k] osq_lock after patch: 9.99% sched-messaging [kernel.vmlinux] [k] mutex_unlock 5.28% sched-messaging [unknown] [H] 0xc0000000000768e0 4.27% sched-messaging [kernel.vmlinux] [k] __copy_tofrom_user_power7 3.77% sched-messaging [kernel.vmlinux] [k] copypage_power7 3.24% sched-messaging [kernel.vmlinux] [k] _raw_write_lock_irq 3.02% sched-messaging [kernel.vmlinux] [k] system_call 2.69% sched-messaging [kernel.vmlinux] [k] wait_consider_task Signed-off-by: Pan Xinhui --- kernel/locking/mutex.c | 15 +++++++++++++-- kernel/locking/rwsem-xadd.c | 16 +++++++++++++--- 2 files changed, 26 insertions(+), 5 deletions(-) diff --git a/kernel/locking/mutex.c b/kernel/locking/mutex.c index a70b90d..8927e96 100644 --- a/kernel/locking/mutex.c +++ b/kernel/locking/mutex.c @@ -236,7 +236,13 @@ bool mutex_spin_on_owner(struct mutex *lock, struct task_struct *owner) */ barrier(); - if (!owner->on_cpu || need_resched()) { + /* + * Use vcpu_is_preempted to detech lock holder preemption issue + * and break. vcpu_is_preempted is a macro defined by false if + * arch does not support vcpu preempted check, + */ + if (!owner->on_cpu || need_resched() || + vcpu_is_preempted(task_cpu(owner))) { ret = false; break; } @@ -261,8 +267,13 @@ static inline int mutex_can_spin_on_owner(struct mutex *lock) rcu_read_lock(); owner = READ_ONCE(lock->owner); + + /* + * As lock holder preemption issue, we both skip spinning if task is not + * on cpu or its cpu is preempted + */ if (owner) - retval = owner->on_cpu; + retval = owner->on_cpu && !vcpu_is_preempted(task_cpu(owner)); rcu_read_unlock(); /* * if lock->owner is not set, the mutex owner may have just acquired diff --git a/kernel/locking/rwsem-xadd.c b/kernel/locking/rwsem-xadd.c index 2337b4b..ad0b5bb 100644 --- a/kernel/locking/rwsem-xadd.c +++ b/kernel/locking/rwsem-xadd.c @@ -336,7 +336,11 @@ static inline bool rwsem_can_spin_on_owner(struct rw_semaphore *sem) goto done; } - ret = owner->on_cpu; + /* + * As lock holder preemption issue, we both skip spinning if task is not + * on cpu or its cpu is preempted + */ + ret = owner->on_cpu && !vcpu_is_preempted(task_cpu(owner)); done: rcu_read_unlock(); return ret; @@ -362,8 +366,14 @@ static noinline bool rwsem_spin_on_owner(struct rw_semaphore *sem) */ barrier(); - /* abort spinning when need_resched or owner is not running */ - if (!owner->on_cpu || need_resched()) { + /* + * abort spinning when need_resched or owner is not running or + * owner's cpu is preempted. vcpu_is_preempted is a macro + * defined by false if arch does not support vcpu preempted + * check + */ + if (!owner->on_cpu || need_resched() || + vcpu_is_preempted(task_cpu(owner))) { rcu_read_unlock(); return false; } -- 2.4.11