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    SubjectRe: [RFC 00/79] perf tools: Initial libperf separation
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    > On Jul 24, 2019, at 1:33 AM, Jiri Olsa <jolsa@redhat.com> wrote:
    >
    > On Wed, Jul 24, 2019 at 07:42:50AM +0000, Song Liu wrote:
    >> Hi Jiri,
    >>
    >>> On Jul 21, 2019, at 4:23 AM, Jiri Olsa <jolsa@kernel.org> wrote:
    >>>
    >>> hi,
    >>> we have long term goal to separate some of the perf functionality
    >>> into library. This patchset is initial effort on separating some
    >>> of the interface.
    >>>
    >>> Currently only the basic counting interface is exported, it allows
    >>> to:
    >>> - create cpu/threads maps
    >>> - create evlist/evsel objects
    >>> - add evsel objects into evlist
    >>> - open/close evlist/evsel objects
    >>> - enable/disable events
    >>> - read evsel counts
    >>
    >> Based on my understanding, evsel and evlist are abstractions in
    >> perf utilities. I think most other tools that use perf UAPIs are
    >> not built based on these abstractions. I looked at a few internal
    >
    > AFAICS some abstraction is needed to carry on the needed stuff
    > like mmaps, counts, group links, PMU details (type, cpus..)
    >
    >> tools. Most of them just uses sys_perf_event_open() and struct
    >> perf_event_attr. I am not sure whether these tools would adopt
    >> libperf, as libperf changes their existing concepts/abstractions.
    >
    > well, besides that we wanted to do this separation for tools/* sake,
    > I think that once libperf shares more interface on sampling and pmu
    > events parsing, it will be considerable choice also for out of the
    > tree tools

    Yeah, in tree tools would benefit from it for sure. And they should
    also motivate out of the tree tools to use libperf.

    >
    >>>
    >>> The initial effort was to have total separation of the objects
    >>> from perf code, but it showed not to be a good way. The amount
    >>> of changed code was too big with high chance for regressions,
    >>> mainly because of the code embedding one of the above objects
    >>> statically.
    >>>
    >>> We took the other approach of sharing the objects/struct details
    >>> within the perf and libperf code. This way we can keep perf
    >>> functionality without any major changes and the libperf users
    >>> are still separated from the object/struct details. We can move
    >>> to total libperf's objects separation gradually in future.
    >>
    >> I found some duplicated logic between libperf and perf, for
    >> example, perf_evlist__open() and evlist__open(). Do we plan to
    >> merge them in the future?
    >
    > yea, as I wrote in the perf_evsel__open patch changelog:
    >
    > It's a simplified version of evsel__open without fallback
    > stuff. We can try to merge it in the future to libperf,
    > but it has many glitches.

    I was reading the code in your git tree and missed the change
    log.

    Thanks for the explanations.

    Song


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