On 01/06/2016 12:34 PM, Thomas Gleixner wrote:
> On Wed, 6 Jan 2016, John Stultz wrote:
>> On Wed, Jan 6, 2016 at 5:00 AM, Prarit Bhargava <pra...@redhat.com> wrote:
>>> -ktime_t ktime_get_with_offset(enum tk_offsets offs)
>>> +ktime_t ktime_get_with_offset(enum tk_offsets offs, int trylock)
>>> {
>>> struct timekeeper *tk = &tk_core.timekeeper;
>>> unsigned int seq;
>>> ktime_t base, *offset = offsets[offs];
>>> s64 nsecs;
>>> + unsigned long flags = 0;
>>> +
>>> + if (unlikely(!timekeeping_initialized))
>>> + return ktime_set(0, 0);
>>>
>>> WARN_ON(timekeeping_suspended);
>>>
>>> + if (trylock && !raw_spin_trylock_irqsave(&timekeeper_lock, flags))
>>> + return ktime_set(KTIME_MAX, 0);
>>
>> Wait.. this doesn't make sense. The timekeeper lock is only for reading.
>>
>> What I was suggesting to you off line is to have something that avoids
>> spinning on the seqcounter should if a bug occurs and we IPI all the
>> cpus, that we don't deadlock or block any printk messages.
>
> We could also extend the fast timekeeper with boot/real/tai extensions and use
> that for printk. You can use ktime_get_mono_fast_ns() today.
>
Thanks tglx -- I thought about doing that but was put off by the comments
in __ktime_get_fast_ns() which point out that we could see backwards time
stamps. But I see your point -- I could do the same "last_time_stamp" check
and use "??" in the output.
That's a far better approach here, and unless John has any objections I'll
go with that.
P.
> Thanks,
>
> tglx
>
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