From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from NAM03-BY2-obe.outbound.protection.outlook.com (mail-by2nam03on0133.outbound.protection.outlook.com [104.47.42.133]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-SHA384 (256/256 bits)) (No client certificate requested) by lists.ozlabs.org (Postfix) with ESMTPS id 3rpqtR3hrczDqDT for ; Wed, 13 Jul 2016 04:17:03 +1000 (AEST) Message-ID: <578533FE.9050606@hpe.com> Date: Tue, 12 Jul 2016 14:16:30 -0400 From: Waiman Long MIME-Version: 1.0 To: Juergen Gross CC: Peter Zijlstra , , , , Pan Xinhui , , , , , , , , , , , Subject: Re: [PATCH v2 0/4] implement vcpu preempted check References: <1467124991-13164-1-git-send-email-xinhui.pan@linux.vnet.ibm.com> <20160706065255.GH30909@twins.programming.kicks-ass.net> <5783B6D7.7020903@hpe.com> <57846F02.7000306@suse.com> In-Reply-To: <57846F02.7000306@suse.com> Content-Type: text/plain; charset="ISO-8859-1"; format=flowed List-Id: Linux on PowerPC Developers Mail List List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , On 07/12/2016 12:16 AM, Juergen Gross wrote: > On 11/07/16 17:10, Waiman Long wrote: >> On 07/06/2016 02:52 AM, 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? >>> >>> Waiman, could you see if you can utilize this to get rid of the >>> SPIN_THRESHOLD in qspinlock_paravirt? >> That API is certainly useful to make the paravirt spinlock perform >> better. However, I am not sure if we can completely get rid of the >> SPIN_THRESHOLD at this point. It is not just the kvm, the xen code need >> to be modified as well. > This should be rather easy. The relevant information is included in the > runstate data mapped into kernel memory. I can provide a patch for Xen > if needed. > > > Juergen Thanks for the offering. We will wait until Xinhui's patch comes through before working on the next step. As for the elimination of SPIN_THRESHOLD, the queue head may not always have the right CPU number of the lock holder. So I don't think we can eliminate that for the queue head spinning. I think we can eliminates the SPIN_THRESHOLD spinning for the other queue node vCPUs. Cheers, Longman