On 15.09.23 18:10, Thomas Gleixner wrote:
> On Fri, Aug 18 2023 at 03:20, Peter Hilber wrote:
>> --- a/kernel/time/timekeeping.c
>> +++ b/kernel/time/timekeeping.c
>> @@ -1247,7 +1247,8 @@ int get_device_system_crosststamp(int (*get_time_fn)
>> */
>> now = tk_clock_read(&tk->tkr_mono);
>> interval_start = tk->tkr_mono.cycle_last;
>> - if (!cycle_between(interval_start, cycles, now)) {
>> + if (!cycle_between(interval_start, cycles, now) &&
>> + cycles != interval_start) {
>> clock_was_set_seq = tk->clock_was_set_seq;
>> cs_was_changed_seq = tk->cs_was_changed_seq;
>> cycles = interval_start;
>
> So the explanation in the changelog makes some sense, but this code
> without any further explanation just makes my brain explode.
>
> This whole thing screams for a change to cycle_between() so it becomes:
>
> timestamp_in_interval(start, end, ts)
>
> and make start inclusive and not exclusive, no?
I tried like this in v1 (having 'end' inclusive as well), but didn't like
the effect at the second usage site.
>
> That's actually correct for both usage sites because for interpolation
> the logic is the same. history_begin->cycles is a valid timestamp, no?
AFAIU, with the timestamp_in_interval() change, history_begin->cycles would
become a valid timestamp. To me it looks like
adjust_historical_crosststamp() should then work unmodified for now. But
one would have to be careful with the additional corner case in the future.
So, document the current one-line change, or switch to
timestamp_in_interval()?
Thanks for the review!
Peter
On Fri, Sep 15 2023 at 19:30, Peter Hilber wrote:
> On 15.09.23 18:10, Thomas Gleixner wrote:
>> So the explanation in the changelog makes some sense, but this code
>> without any further explanation just makes my brain explode.
>>
>> This whole thing screams for a change to cycle_between() so it becomes:
>>
>> timestamp_in_interval(start, end, ts)
>>
>> and make start inclusive and not exclusive, no?
>
> I tried like this in v1 (having 'end' inclusive as well), but didn't like
> the effect at the second usage site.
>
>>
>> That's actually correct for both usage sites because for interpolation
>> the logic is the same. history_begin->cycles is a valid timestamp, no?
>
> AFAIU, with the timestamp_in_interval() change, history_begin->cycles would
> become a valid timestamp. To me it looks like
> adjust_historical_crosststamp() should then work unmodified for now. But
> one would have to be careful with the additional corner case in the future.
>
> So, document the current one-line change, or switch to
> timestamp_in_interval()?
I really prefer the consistent function which treats the start as
inclusive as that makes the most sense and is self explanatory.
Thanks,
tglx