Re: [PATCH] perf arm-spe: Fix incorrect sample timestamp in perf script

[Yang Jihong]

Hello Leo,

On 2021/6/28 15:29, Leo Yan wrote:
> On Mon, Jun 28, 2021 at 02:30:56PM +0800, Yang Jihong wrote:
> > Hello Leo,
> >
> > On 2021/6/28 12:07, Leo Yan wrote:
> > > On Mon, Jun 28, 2021 at 11:45:07AM +0800, Yang Jihong wrote:
> > >
> > > [...]
> > >
> > > > The timestamp does not match. Each timestamp has a difference of
> > > > 213.98296702 seconds. Is the command I executed wrong?
> > >
> > > I don't understand what's your meaning "a difference of 213.98296702
> > > seconds".
> > >
> > > But let me give an explaination with your below examples.  You could
> > > the command "perf script" outputs the timestamp 314938.859071370 which
> > > is the kernel's timestamp, if using the command "perf script -D", it
> > > outputs the value 31515284203839 which is the Arch timer's raw counter
> > > value.
> > >
> > > In theory, the arch timer's counter is enabled at the very early
> > > time before kernel's booting (e.g. bootloaders, UEFI, etc...).  So for
> > > the kernel's timestamp, it should calibrate the timestamp and reduce
> > > the offset prior to the kernel's booting.  I think this is the reason
> > > why you observed 213.98296702 seconds difference (if compared with
> > > your own patch?)
> > >
> > > If still see any issue, please let me know.  Thanks a lot for the
> > > testing!
> > Thanks for the very detailed explanation.
> > To keep the correct relative time sequence between events in SPE and other
> > events, we should use kernel timestamp instead of arch time. Therefore, we
> > need to calibrate the time. Is this correct?
>
> Yes, correct!
I see. Thank you for your answer.:)

Jihong
> .