Re: [PATCH 1/3] timekeeping: NMI safe converter from a given time to monotonic

[Stephane Eranian]

On Tue, Jan 24, 2023 at 12:52 AM Thomas Gleixner <tglx@xxxxxxxxxxxxx> wrote:
>
> On Mon, Jan 23 2023 at 10:27, kan liang wrote:
> > From: Kan Liang <kan.liang@xxxxxxxxxxxxxxx>
> >
> > It's useful to provide a NMI safe function to convert a given time to
> > monotonic. For example, the perf_event subsystem wants to convert a TSC
> > of a PEBS record to a monotonic clock in a NMI handler.
>
> Why? That's a postprocessing problem, really.
>
Because you want to correlate samples captured by PEBS with samples
from applications timestamped with a user available clock such as
CLOCK_MONOTONIC, for instance.
When I create a perf_event event and I stipulate that
event_attr.clockid=MONOTONIC, I expect all the samples from
that event to be timestamped using the same clock source, regardless
of PEBS or IBS.



> Thanks,
>
>         tglx