Re: [PATCH 1/8] perf cs-etm: Don't flush when packet_queue fills up

[James Clark]

On 11/09/2024 09:14, Leo Yan wrote:
> On 9/10/2024 9:28 PM, Leo Yan wrote:
> > On 9/5/2024 11:50 AM, James Clark wrote:
> >
> > [...]
> >
> > > cs_etm__flush(), like cs_etm__sample() is an operation that generates a
> > > sample and then swaps the current with the previous packet. Calling
> > > flush after processing the queues results in two swaps which corrupts
> > > the next sample. Therefore it wasn't appropriate to call flush here so
> > > remove it.
> >
> > In the cs_etm__sample(), if the period is not overflow, it is not necessarily
> > to generate instruction samples and copy back stack entries. This is why we
> > want to call cs_etm__flush() to make sure the last packet can be recorded
> > properly for instruction sample with back stacks.
> >
> > We also need to take account into the case for the end of the session - in
> > this case we need to generate samples for the last packet for complete info.
> >
> > I am wandering should we remove the cs_etm__packet_swap() from cs_etm__sample()?
>
> Sorry for typo. I meant to remove the cs_etm__packet_swap() from cs_etm__flush().
>
> Thanks,
> Leo

Turns out there was already cs_etm__end_block() for the end of the 
session, but it was only called for the timeless modes. I added it for 
timestamped mode too in V2.

I also kept the existing flush() function for discontinuities. I changed 
my mind that the differences to cs_etm__sample() weren't relevant.

So I think we still need to keep the swap in flush() because otherwise 
the next sample won't start from the right place.