Re: [KVM TSC trapping / migration 1/2] Add TSC trapping for SVM and VMX

Avi Kivity
2011-01-06T11:32:18Z

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.

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error compiling committee.c: too many arguments to function