Messages in this thread | | | Date | Tue, 12 Jul 2016 14:16:30 -0400 | From | Waiman Long <> | Subject | Re: [PATCH v2 0/4] implement vcpu preempted check |
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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
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