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

Zachary Amsden
2010-06-15T21:03:47Z

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.

Zach