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SubjectRe: [KVM timekeeping 17/35] Implement getnsboottime kernel API
Zachary Amsden wrote:
> On 08/27/2010 08:05 AM, Jan Kiszka wrote:
>> Zachary Amsden wrote:
>>
>>> Add a kernel call to get the number of nanoseconds since boot. This
>>> is generally useful enough to make it a generic call.
>>>
>>> Signed-off-by: Zachary Amsden<zamsden@redhat.com>
>>> ---
>>> include/linux/time.h | 1 +
>>> kernel/time/timekeeping.c | 27 +++++++++++++++++++++++++++
>>> 2 files changed, 28 insertions(+), 0 deletions(-)
>>>
>>> diff --git a/include/linux/time.h b/include/linux/time.h
>>> index ea3559f..5d04108 100644
>>> --- a/include/linux/time.h
>>> +++ b/include/linux/time.h
>>> @@ -145,6 +145,7 @@ extern void getnstimeofday(struct timespec *tv);
>>> extern void getrawmonotonic(struct timespec *ts);
>>> extern void getboottime(struct timespec *ts);
>>> extern void monotonic_to_bootbased(struct timespec *ts);
>>> +extern s64 getnsboottime(void);
>>>
>>> extern struct timespec timespec_trunc(struct timespec t, unsigned gran);
>>> extern int timekeeping_valid_for_hres(void);
>>> diff --git a/kernel/time/timekeeping.c b/kernel/time/timekeeping.c
>>> index caf8d4d..d250f0a 100644
>>> --- a/kernel/time/timekeeping.c
>>> +++ b/kernel/time/timekeeping.c
>>> @@ -285,6 +285,33 @@ void ktime_get_ts(struct timespec *ts)
>>> }
>>> EXPORT_SYMBOL_GPL(ktime_get_ts);
>>>
>>> +
>>> +/**
>>> + * getnsboottime - get the bootbased clock in nsec format
>>> + *
>>> + * The function calculates the bootbased clock from the realtime
>>> + * clock and the wall_to_monotonic offset and stores the result
>>> + * in normalized timespec format in the variable pointed to by @ts.
>>> + */
>>>
>> This thing is not returning anything in some ts variable. And I also had
>> a hard time spotting the key difference to getboottime - the name is
>> really confusing.
>>
>> Besides this, if you have good suggestion how to provide a compat
>> version for older kernels, I'm all ears. Please also have a careful look
>> at kvm-kmod's kvm_getboottime again, right now I'm a bit confused about
>> what it is supposed to return and what it actually does (note that
>> kvm-kmod cannot account for time spent in suspend state).
>>
>> Thanks!
>> Jan
>>
>>
>>> +s64 getnsboottime(void)
>>> +{
>>> + unsigned int seq;
>>> + s64 secs, nsecs;
>>> +
>>> + WARN_ON(timekeeping_suspended);
>>> +
>>> + do {
>>> + seq = read_seqbegin(&xtime_lock);
>>> + secs = xtime.tv_sec + wall_to_monotonic.tv_sec;
>>> + secs += total_sleep_time.tv_sec;
>>> + nsecs = xtime.tv_nsec + wall_to_monotonic.tv_nsec;
>>> + nsecs += total_sleep_time.tv_nsec + timekeeping_get_ns();
>>> +
>>> + } while (read_seqretry(&xtime_lock, seq));
>>> + return nsecs + (secs * NSEC_PER_SEC);
>>> +}
>>> +EXPORT_SYMBOL_GPL(getnsboottime);
>>> +
>>> /**
>>> * do_gettimeofday - Returns the time of day in a timeval
>>> * @tv: pointer to the timeval to be set
>>>
>>
>
> Yes, we should probably change the name before making this an actual
> kernel API, John made some better suggestions.
>
> For kvm-kmod, the following conversion should work:
>
> 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);
> }
>
> The only real point to getnsboottime is to stop the unnecessary
> conversions, but looking at it now, it doesn't appear to actually save
> any, does it? Maybe it is better to just drop the thing all-together.

It looks like. Will you post a removal patch kvm.git? I'll better wait
with updating kvm-kmod then.

Jan

--
Siemens AG, Corporate Technology, CT T DE IT 1
Corporate Competence Center Embedded Linux


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