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

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Message-ID: <4C18877E.9070605@redhat.com>
Date:	Wed, 16 Jun 2010 16:12:46 +0800
From:	Jason Wang <jasowang@...hat.com>
To:	Zachary Amsden <zamsden@...hat.com>
CC:	Avi Kivity <avi@...hat.com>, 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

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@...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.
>
>   
Yes we should.
> Zach
> --
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>   

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