Messages in this thread | | | Date | Thu, 27 Jan 2011 15:15:50 +0200 | From | Avi Kivity <> | Subject | Re: [PATCH v3 1/3] KVM: fix rcu usage warning in kvm_arch_vcpu_ioctl_set_sregs() |
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On 01/20/2011 05:27 PM, Marcelo Tosatti wrote: > > Before patch: > > > > real 5m6.493s > > user 3m57.847s > > sys 9m7.115s > > > > real 5m1.750s > > user 4m0.109s > > sys 9m10.192s > > > > > > After patch: > > real 5m0.140s > > user 3m57.956s > > sys 8m58.339s > > > > real 4m56.314s > > user 4m0.303s > > sys 8m55.774s > > Nice. One disadvantageous side effect for the kvm_vcpu_kick path > is that it can race with make_all_cpus_request, which is possibly > doing unrelated, slower work (IPI'ing other vcpus, waiting for > response).
I think we're fine here. The kvm_vcpu_kick() check is
me = get_cpu(); if (cpu != me&& (unsigned)cpu< nr_cpu_ids&& cpu_online(cpu)) - if (atomic_xchg(&vcpu->guest_mode, 0)) + if (kvm_vcpu_exiting_guest_mode(vcpu) == IN_GUEST_MODE) smp_send_reschedule(cpu); put_cpu();
even if it did race, ->mode becomes EXITING_GUEST_MODE and we still avoid the IPI. Note that make_all_cpus_request() cleverly checks for != OUTSIDE_GUEST_MODE, so if it loses the race with kvm_vcpu_kick(), it still sends the IPI to be sure the vcpu loop sees vcpu->requests in time.
> Looks ok, but lets wait for more careful reviews before applying.
Patches applied.
-- error compiling committee.c: too many arguments to function
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