Re: [PATCH 12/17] Add helper function get_kernel_ns

Glauber Costa
2010-06-16T14:03:31Z

On Wed, Jun 16, 2010 at 04:12:46PM +0800, Jason Wang wrote:
> Zachary Amsden wrote:
> > On 06/14/2010 10:41 PM, Avi Kivity wrote:
> >
> >> On 06/15/2010 10:34 AM, Zachary Amsden wrote:
> >>
> >>> Add a helper function for the multiple places this is used. Note
> >>> that it
> >>> must not be called in preemptible context, as that would mean the kernel
> >>> could enter software suspend state, which would cause non-atomic
> >>> operation
> >>> of the monotonic_to_bootbased computation.
> >>>
> >>> Open question: should the KVM_SET_CLOCK / KVM_GET_CLOCK ioctls use this
> >>> as well? Currently, they are not bootbased (but perhaps should be).
> >>>
> >>> Signed-off-by: Zachary Amsden<zamsden@redhat.com>
> >>> ---
> >>> arch/x86/kvm/x86.c | 26 +++++++++++++-------------
> >>> 1 files changed, 13 insertions(+), 13 deletions(-)
> >>>
> >>> diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
> >>> index 703ea43..15c7317 100644
> >>> --- a/arch/x86/kvm/x86.c
> >>> +++ b/arch/x86/kvm/x86.c
> >>> @@ -915,6 +915,16 @@ static void kvm_get_time_scale(uint32_t
> >>> scaled_khz, uint32_t base_khz,
> >>> __func__, base_khz, scaled_khz, shift, *pmultiplier);
> >>> }
> >>>
> >>> +static inline u64 get_kernel_ns(void)
> >>> +{
> >>> + struct timespec ts;
> >>> +
> >>> + WARN_ON(preemptible());
> >>> + ktime_get_ts(&ts);
> >>> + monotonic_to_bootbased(&ts);
> >>> + return timespec_to_ns(&ts);
> >>> +}
> >>> +
> >>> static DEFINE_PER_CPU(unsigned long, cpu_tsc_khz);
> >>>
> >>>
> >> Isn't something like this a candidate for the time infrastructure?
> >>
> >>
> >
> > Should it be? It certainly seems reasonable.
> >
> >
> > Also, should we be using it for the cases KVM_GET_CLOCK /
> > KVM_SET_CLOCK? It seems global kvmclock_offset for the VM ignores the
> > bootbased conversion.
> >
> >
> Yes we should.
indeed. Also shows the importance of doing it in a central place.
Have we had an acessor like that before, we would probably not have
made this mistake.