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    SubjectRe: [KVM TSC trapping / migration 1/2] Add TSC trapping for SVM and VMX
    On 01/06/2011 01:32 AM, Avi Kivity wrote:
    > On 01/06/2011 12:10 PM, Zachary Amsden wrote:
    >> Reasons to trap the TSC are numerous, but we want to avoid it as much
    >> as possible for performance reasons.
    >>
    >> We provide two conservative modes via modules parameters and userspace
    >> hinting. First, the module can be loaded with "tsc_auto=1" as a module
    >> parameter, which turns on conservative TSC trapping only when it is
    >> required (when unstable TSC or faster KHZ CPU is detected).
    >>
    >> For userspace hinting, we enable trapping only if necessary. Userspace
    >> can hint that a VM needs a fixed frequency TSC, and also that SMP
    >> stability will be required. In that case, we conservatively turn on
    >> trapping when it is needed. In addition, users may now specify the
    >> desired TSC rate at which to run. If this rate differs significantly
    >> from the host rate, trapping will be enabled.
    >>
    >> There is also an override control to allow TSC trapping to be turned on
    >> or off unconditionally for testing.
    >>
    >> We indicate to pvclock users that the TSC is being trapped, to allow
    >> avoiding overhead and directly using RDTSCP (only for SVM). This
    >> optimization is not yet implemented.
    >>
    >> Signed-off-by: Zachary Amsden<zamsden@redhat.com>
    >> ---
    >> arch/x86/include/asm/kvm_host.h | 6 +-
    >> arch/x86/include/asm/pvclock-abi.h | 1 +
    >> arch/x86/kvm/svm.c | 20 ++++++
    >> arch/x86/kvm/vmx.c | 21 +++++++
    >> arch/x86/kvm/x86.c | 113
    >> +++++++++++++++++++++++++++++++++---
    >> arch/x86/kvm/x86.h | 2 +
    >> include/linux/kvm.h | 15 +++++
    >> 7 files changed, 168 insertions(+), 10 deletions(-)
    >
    >
    > Haven't reviewed yet, but Documentation/kvm/api.txt is missing here.
    >

    That will be included when I port to upstream head. When dealing with
    software documentation, too much is never enough.

    Zach


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