2016-07-06 20:28 GMT+08:00 Paolo Bonzini <pbonzini@xxxxxxxxxx>: > > > On 06/07/2016 14:08, Wanpeng Li wrote: >> 2016-07-06 18:44 GMT+08:00 Paolo Bonzini <pbonzini@xxxxxxxxxx>: >>> >>> >>> 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 -- To unsubscribe from this list: send the line "unsubscribe kvm" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
