Rdpmc topdown

[willowec]

Pull Request Description

This PR fixes #207

Intel's topdown events, if opened using perf_event's perf_event_open() behave differently when read using read() than when they are read using rdpmc(). This has a few unfortunate consequences. When a topdown event is read using read() you get a value that is the number of slots recorded for that topdown category. So to get, for example, the percentage of slots that were retiring, you divide the value of TOPDOWN:RETIRING_SLOTS by the value of TOPDOWN:SLOTS and multiply the result by 100.

However, when any topdown event is read using rdpmc(), the result is always one value containing eight 8-bit percentages, no matter which event was read:

     | mem_bound | fetch_lat | br_mispred | heavy_ops | be_bound | fe_bound | bad_spec | retiring
0x   | XX        | XX        | XX         | XX        | XX       | XX       | XX       | XX

In order to extract a percentage from this, you would instead do some shifting and masking as described in tools/perf/Documentation/topdown.txt

This means that storing and accumulating the values of topdown events makes sense only when rdpmc is disabled in PAPI. In order to account for this, an additional metric field was added to perf_event component's pe_event_info_t struct, and is set during initialization for events matching the TOPDOWN base event. Events with this field set no longer have their reset flag cleared when rdpmc is enabled.

A new validation test, topdown_validation.c is added to verify that the results PAPI obtains agree with a direct call to rdpmc()

Because this patch was developed on an Intel Raptorlake machine, some other additions were also necessary to enable the development of this PR:

• Missing topdown events were added to the adl_glc events header file in libpfm4 (we are still waiting to hear back having this patch added to libpfm4 officially)
• Preset events were added to papi_events.csv for the adl_glc architecture

Author Checklist

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[willowec]

Converting to a draft as not all of the tests are passing for raptorlake

[willowec]

Un-drafting as the failing tests are in the sysdetect component and are due to the heterogeneity of the Raptorlake architecture, unrelated to the contributions of this patch.