From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mx0a-001b2d01.pphosted.com (mx0a-001b2d01.pphosted.com [148.163.156.1]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by lists.ozlabs.org (Postfix) with ESMTPS id 3rf2VN5BRszDqs1 for ; Tue, 28 Jun 2016 20:44:12 +1000 (AEST) Received: from pps.filterd (m0098399.ppops.net [127.0.0.1]) by mx0a-001b2d01.pphosted.com (8.16.0.11/8.16.0.11) with SMTP id u5SAcwoO100765 for ; Tue, 28 Jun 2016 06:44:11 -0400 Received: from e35.co.us.ibm.com (e35.co.us.ibm.com [32.97.110.153]) by mx0a-001b2d01.pphosted.com with ESMTP id 23sp42b5ey-1 (version=TLSv1.2 cipher=AES256-SHA bits=256 verify=NOT) for ; Tue, 28 Jun 2016 06:44:10 -0400 Received: from localhost by e35.co.us.ibm.com with IBM ESMTP SMTP Gateway: Authorized Use Only! Violators will be prosecuted for from ; Tue, 28 Jun 2016 04:44:10 -0600 From: Pan Xinhui To: linux-kernel@vger.kernel.org, linuxppc-dev@lists.ozlabs.org, virtualization@lists.linux-foundation.org, linux-s390@vger.kernel.org Cc: peterz@infradead.org, mingo@redhat.com, mpe@ellerman.id.au, paulus@samba.org, benh@kernel.crashing.org, paulmck@linux.vnet.ibm.com, waiman.long@hpe.com, will.deacon@arm.com, boqun.feng@gmail.com, dave@stgolabs.net, schwidefsky@de.ibm.com, Pan Xinhui Subject: [PATCH v2 4/4] kernel/locking: Drop the overload of {mutex, rwsem}_spin_on_owner Date: Tue, 28 Jun 2016 10:43:11 -0400 In-Reply-To: <1467124991-13164-1-git-send-email-xinhui.pan@linux.vnet.ibm.com> References: <1467124991-13164-1-git-send-email-xinhui.pan@linux.vnet.ibm.com> Message-Id: <1467124991-13164-5-git-send-email-xinhui.pan@linux.vnet.ibm.com> List-Id: Linux on PowerPC Developers Mail List List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , 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 79d2d76..ef0451b2 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 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 09e30c6..828ca7c 100644 --- a/kernel/locking/rwsem-xadd.c +++ b/kernel/locking/rwsem-xadd.c @@ -319,7 +319,11 @@ 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 not + * on cpu or its cpu is preempted + */ + ret = owner->on_cpu && !vcpu_is_preempted(task_cpu(owner)); done: rcu_read_unlock(); return ret; @@ -340,8 +344,14 @@ bool rwsem_spin_on_owner(struct rw_semaphore *sem, struct task_struct *owner) */ 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