Re: Perf ABI versioning

[Jean Pihet <jean.pihet@newoldbits.com>]

Hi Thomas,

On Mon, Jan 24, 2011 at 5:04 PM, Thomas Renninger <trenn@suse.de> wrote:
> Hi,
>
> as I recently cleaned up the power events with
> some format/abi adjustings...
>
> I realized that it was rather easy to adjust
> the stuff in drivers/tools/perf, because there
> are some nice facilities to query which events
> are available.
>
> I looked at pytimechart, there it's not that nice
> and convenient would be some kind of version number.
>
> pytimechart can parse traces which are simply copied
> away from /sys/kernel/debug/trace and to check for
> available events and their format, one would have to
> do a separate, ugly to implement, iteration of parsing.
>
> Would it make sense to introduce a trace
> ABI version number?
> It would be enough to increase it by one every time
> any event (don't know about other perf facilities) is
> added, removed or modified.
> Ideally the modifications are tracked with a short
> description in a file like Documentation/trace/format.changes
>
> Untested, but the patch at the end should simply add
> a version number on top of
> /sys/kernel/debug/trace file

If needed the ABI versioning should at least contain a major and minor
number, i.e. 'x.y'.

The big question IMO is if it is needed or not. Is this a real problem
in the userland? Are the apps always fitting the kernel ABI in a
packaged distro?

>
> While this should be enough for the kernel, perf record
> would need to include it into it's binary perf.data format
> as well?
>
> Then userspace apps could easily test whether supported
> events would be included at all, whether only a subset of
> supported events were made available and which format they have.
>
> Does this make sense?
>
> Thanks,
>
>    Thomas
>

Regards,
Jean
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