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

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Message-ID: <1276636400.1703.21.camel@localhost>
Date:	Tue, 15 Jun 2010 14:13:20 -0700
From:	john stultz <johnstul@...ibm.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, Thomas Gleixner <tglx@...utronix.de>
Subject: Re: [PATCH 12/17] Add helper function get_kernel_ns

On Tue, 2010-06-15 at 11:03 -1000, 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.

Yea, probably should move to timekeeping.c or time.h.

You might also want a more descriptive name, since get_kernel_ns()
doesn't really express that this is the bootbased monotonic time. 

The similar sounding current_kernel_time() returns a coarse tick
granular CLOCK_REALTIME, so it could lead to confusion.

thanks
-john


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