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

Jason Wang
2010-06-16T08:07:18Z

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.
> Zach
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