linux-kernel - Re: [PATCH 12/17] Add helper function get_kernel

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Date:	Tue, 15 Jun 2010 11:03:33 -1000
From:	Zachary Amsden <zamsden@...hat.com>
To:	Avi Kivity <avi@...hat.com>
CC:	mtosatti@...hat.com, glommer@...hat.com, kvm@...r.kernel.org,
	linux-kernel@...r.kernel.org, john stultz <johnstul@...ibm.com>,
	Thomas Gleixner <tglx@...utronix.de>
Subject: Re: [PATCH 12/17] Add helper function get_kernel_ns

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@...hat.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
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