Re: [PATCH 4/5] perf arm-spe: Implement find_snapshot callback

Will Deacon
2021-10-12T08:20:02Z

On Mon, Oct 11, 2021 at 04:55:37PM +0100, German Gomez wrote:
> Hi Leo,
>
> On 06/10/2021 10:51, Leo Yan wrote:
> > On Wed, Oct 06, 2021 at 10:35:20AM +0100, German Gomez wrote:
> >
> > [...]
> >
> >>> So simply say, I think the head pointer monotonically increasing is
> >>> the right thing to do in Arm SPE driver.
> >> I will talk to James about how we can proceed on this.
> > Thanks!
>
> I took this offline with James and, though it looks possible to patch
> the SPE driver to have a monotonically increasing head pointer in order
> to simplify the handling in the perf tool, it could be a breaking change
> for users of the perf_event_open syscall that currently rely on the way
> it works now.
>
> An alternative way we considered to simplify the patch is to change the
> logic inside the find_snapshot callback so that it records the entire
> contents of the aux buffer every time.
>
> What do you think?

What does intel-pt do?

Will