From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754140AbcGFMax (ORCPT ); Wed, 6 Jul 2016 08:30:53 -0400 Received: from mx1.redhat.com ([209.132.183.28]:45430 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751201AbcGFMav (ORCPT ); Wed, 6 Jul 2016 08:30:51 -0400 Subject: Re: [PATCH v2 0/4] implement vcpu preempted check To: Wanpeng Li 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> 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 From: Paolo Bonzini Message-ID: <8e8edf1b-b64b-3c44-b580-b9271663844c@redhat.com> Date: Wed, 6 Jul 2016 14:28:06 +0200 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:45.0) Gecko/20100101 Thunderbird/45.1.1 MIME-Version: 1.0 In-Reply-To: Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: 8bit X-Greylist: Sender IP whitelisted, not delayed by milter-greylist-4.5.16 (mx1.redhat.com [10.5.110.31]); Wed, 06 Jul 2016 12:29:53 +0000 (UTC) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org 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. Paolo