From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754428AbcGFNDG (ORCPT ); Wed, 6 Jul 2016 09:03:06 -0400 Received: from mail-oi0-f68.google.com ([209.85.218.68]:35519 "EHLO mail-oi0-f68.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751622AbcGFNDE (ORCPT ); Wed, 6 Jul 2016 09:03:04 -0400 MIME-Version: 1.0 In-Reply-To: <8e8edf1b-b64b-3c44-b580-b9271663844c@redhat.com> References: <1467124991-13164-1-git-send-email-xinhui.pan@linux.vnet.ibm.com> <20160706065255.GH30909@twins.programming.kicks-ass.net> <14a24854-9787-e4a1-c9a8-76eba4e97301@redhat.com> <8e8edf1b-b64b-3c44-b580-b9271663844c@redhat.com> From: Wanpeng Li Date: Wed, 6 Jul 2016 21:03:01 +0800 Message-ID: Subject: Re: [PATCH v2 0/4] implement vcpu preempted check To: Paolo Bonzini Cc: Peter Zijlstra , Pan Xinhui , linux-s390 , Davidlohr Bueso , mpe@ellerman.id.au, boqun.feng@gmail.com, will.deacon@arm.com, "linux-kernel@vger.kernel.org" , Waiman Long , virtualization@lists.linux-foundation.org, Ingo Molnar , Paul Mackerras , benh@kernel.crashing.org, schwidefsky@de.ibm.com, Paul McKenney , linuxppc-dev@lists.ozlabs.org, kvm Content-Type: text/plain; charset=UTF-8 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org 2016-07-06 20:28 GMT+08:00 Paolo Bonzini : > > > On 06/07/2016 14:08, Wanpeng Li wrote: >> 2016-07-06 18:44 GMT+08:00 Paolo Bonzini : >>> >>> >>> On 06/07/2016 08:52, Peter Zijlstra wrote: >>>> On Tue, Jun 28, 2016 at 10:43:07AM -0400, Pan Xinhui wrote: >>>>> change fomr v1: >>>>> a simplier definition of default vcpu_is_preempted >>>>> skip mahcine type check on ppc, and add config. remove dedicated macro. >>>>> add one patch to drop overload of rwsem_spin_on_owner and mutex_spin_on_owner. >>>>> add more comments >>>>> thanks boqun and Peter's suggestion. >>>>> >>>>> This patch set aims to fix lock holder preemption issues. >>>>> >>>>> test-case: >>>>> perf record -a perf bench sched messaging -g 400 -p && perf report >>>>> >>>>> 18.09% sched-messaging [kernel.vmlinux] [k] osq_lock >>>>> 12.28% sched-messaging [kernel.vmlinux] [k] rwsem_spin_on_owner >>>>> 5.27% sched-messaging [kernel.vmlinux] [k] mutex_unlock >>>>> 3.89% sched-messaging [kernel.vmlinux] [k] wait_consider_task >>>>> 3.64% sched-messaging [kernel.vmlinux] [k] _raw_write_lock_irq >>>>> 3.41% sched-messaging [kernel.vmlinux] [k] mutex_spin_on_owner.is >>>>> 2.49% sched-messaging [kernel.vmlinux] [k] system_call >>>>> >>>>> We introduce interface bool vcpu_is_preempted(int cpu) and use it in some spin >>>>> loops of osq_lock, rwsem_spin_on_owner and mutex_spin_on_owner. >>>>> These spin_on_onwer variant also cause rcu stall before we apply this patch set >>>> >>>> Paolo, could you help out with an (x86) KVM interface for this? >>> >>> If it's just for spin loops, you can check if the version field in the >>> steal time structure has changed. >> >> Steal time will not be updated until ahead of next vmentry except >> wrmsr MSR_KVM_STEAL_TIME. So it can't represent it is preempted >> currently, right? > > Hmm, you're right. We can use bit 0 of struct kvm_steal_time's flags to > indicate that pad[0] is a "VCPU preempted" field; if pad[0] is 1, the > VCPU has been scheduled out since the last time the guest reset the bit. > The guest can use an xchg to test-and-clear it. The bit can be > accessed at any time, independent of the version field. I will try to implement it tomorrow, thanks for your proposal. :) Regards, Wanpeng Li From mboxrd@z Thu Jan 1 00:00:00 1970 From: Wanpeng Li Subject: Re: [PATCH v2 0/4] implement vcpu preempted check Date: Wed, 6 Jul 2016 21:03:01 +0800 Message-ID: References: <1467124991-13164-1-git-send-email-xinhui.pan@linux.vnet.ibm.com> <20160706065255.GH30909@twins.programming.kicks-ass.net> <14a24854-9787-e4a1-c9a8-76eba4e97301@redhat.com> <8e8edf1b-b64b-3c44-b580-b9271663844c@redhat.com> Mime-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Cc: linux-s390 , Davidlohr Bueso , benh@kernel.crashing.org, kvm , Peter Zijlstra , Pan Xinhui , boqun.feng@gmail.com, will.deacon@arm.com, "linux-kernel@vger.kernel.org" , Waiman Long , virtualization@lists.linux-foundation.org, Ingo Molnar , Paul Mackerras , mpe@ellerman.id.au, schwidefsky@de.ibm.com, Paul McKenney , linuxppc-dev@lists.ozlabs.org To: Paolo Bonzini Return-path: In-Reply-To: <8e8edf1b-b64b-3c44-b580-b9271663844c@redhat.com> List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Sender: virtualization-bounces@lists.linux-foundation.org Errors-To: virtualization-bounces@lists.linux-foundation.org List-Id: kvm.vger.kernel.org 2016-07-06 20:28 GMT+08:00 Paolo Bonzini : > > > On 06/07/2016 14:08, Wanpeng Li wrote: >> 2016-07-06 18:44 GMT+08:00 Paolo Bonzini : >>> >>> >>> On 06/07/2016 08:52, Peter Zijlstra wrote: >>>> On Tue, Jun 28, 2016 at 10:43:07AM -0400, Pan Xinhui wrote: >>>>> change fomr v1: >>>>> a simplier definition of default vcpu_is_preempted >>>>> skip mahcine type check on ppc, and add config. remove dedicated macro. >>>>> add one patch to drop overload of rwsem_spin_on_owner and mutex_spin_on_owner. >>>>> add more comments >>>>> thanks boqun and Peter's suggestion. >>>>> >>>>> This patch set aims to fix lock holder preemption issues. >>>>> >>>>> test-case: >>>>> perf record -a perf bench sched messaging -g 400 -p && perf report >>>>> >>>>> 18.09% sched-messaging [kernel.vmlinux] [k] osq_lock >>>>> 12.28% sched-messaging [kernel.vmlinux] [k] rwsem_spin_on_owner >>>>> 5.27% sched-messaging [kernel.vmlinux] [k] mutex_unlock >>>>> 3.89% sched-messaging [kernel.vmlinux] [k] wait_consider_task >>>>> 3.64% sched-messaging [kernel.vmlinux] [k] _raw_write_lock_irq >>>>> 3.41% sched-messaging [kernel.vmlinux] [k] mutex_spin_on_owner.is >>>>> 2.49% sched-messaging [kernel.vmlinux] [k] system_call >>>>> >>>>> We introduce interface bool vcpu_is_preempted(int cpu) and use it in some spin >>>>> loops of osq_lock, rwsem_spin_on_owner and mutex_spin_on_owner. >>>>> These spin_on_onwer variant also cause rcu stall before we apply this patch set >>>> >>>> Paolo, could you help out with an (x86) KVM interface for this? >>> >>> If it's just for spin loops, you can check if the version field in the >>> steal time structure has changed. >> >> Steal time will not be updated until ahead of next vmentry except >> wrmsr MSR_KVM_STEAL_TIME. So it can't represent it is preempted >> currently, right? > > Hmm, you're right. We can use bit 0 of struct kvm_steal_time's flags to > indicate that pad[0] is a "VCPU preempted" field; if pad[0] is 1, the > VCPU has been scheduled out since the last time the guest reset the bit. > The guest can use an xchg to test-and-clear it. The bit can be > accessed at any time, independent of the version field. I will try to implement it tomorrow, thanks for your proposal. :) Regards, Wanpeng Li