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. Paolo _______________________________________________ Virtualization mailing list Virtualization@xxxxxxxxxxxxxxxxxxxxxxxxxx https://lists.linuxfoundation.org/mailman/listinfo/virtualization
