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    SubjectRe: [PATCH 2/3] KVM: send IPI to vcpu only when it's in guest mode
    On 01/05/2011 05:48 PM, Avi Kivity wrote:
    > On 01/05/2011 11:38 AM, Xiao Guangrong wrote:
    >> We can interrupt the vcpu only when it's running in guest mode
    >> to reduce IPI.
    >>
    >> It looks like only ia64 and x86 need to send IPI to other vcpus, so
    >> i only add the implementation of 'vcpu->guest_mode' in ia64, but i
    >> don't know ia64 well, please point out the right way for me if the
    >> implementation is incorrect
    >>
    >> And ia64 is not tested since i don't have ia64 box
    >>
    >> Signed-off-by: Xiao Guangrong<xiaoguangrong@cn.fujitsu.com>
    >> ---
    >> arch/ia64/kvm/kvm-ia64.c | 2 ++
    >> virt/kvm/kvm_main.c | 3 ++-
    >> 2 files changed, 4 insertions(+), 1 deletions(-)
    >>
    >> diff --git a/arch/ia64/kvm/kvm-ia64.c b/arch/ia64/kvm/kvm-ia64.c
    >> index 70d224d..15c11b2 100644
    >> --- a/arch/ia64/kvm/kvm-ia64.c
    >> +++ b/arch/ia64/kvm/kvm-ia64.c
    >> @@ -662,6 +662,7 @@ again:
    >> goto vcpu_run_fail;
    >>
    >> srcu_read_unlock(&vcpu->kvm->srcu, idx);
    >> + atomic_set(&vcpu->guest_mode, 1);
    >> kvm_guest_enter();
    >
    > I think it needs an smp_wmb() (technically x86 needs it too, but x86 is strongly ordered)
    >

    Hi Avi,

    After read the code of ia64 more carefully, i noticed ia64 doesn't check 'vcpu->requests'
    before go to guest mode, so it means we no need memory barrier here? right?

    Certainly, we need an smb_mb between setting vcpu->mode and checking vcpu->request in x86.


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