linux-kernel - [PATCH v3 0/4] perf: Support PERF_SAMPLE_READ with inherit

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Date: Fri, 22 Mar 2024 13:04:10 +0000
From: Ben Gainey <ben.gainey@....com>
To: peterz@...radead.org,
	mingo@...hat.com,
	acme@...nel.org,
	namhyung@...nel.org
Cc: james.clark@....com,
	mark.rutland@....com,
	alexander.shishkin@...ux.intel.com,
	jolsa@...nel.org,
	irogers@...gle.com,
	adrian.hunter@...el.com,
	linux-perf-users@...r.kernel.org,
	linux-kernel@...r.kernel.org,
	Ben Gainey <ben.gainey@....com>
Subject: [PATCH v3 0/4] perf: Support PERF_SAMPLE_READ with inherit_stat

This change allows events to use PERF_SAMPLE READ with inherit so long 
as both inherit_stat and PERF_SAMPLE_TID are set.

Currently it is not possible to use PERF_SAMPLE_READ with inherit. This 
restriction assumes the user is interested in collecting aggregate 
statistics as per `perf stat`. It prevents a user from collecting 
per-thread samples using counter groups from a multi-threaded or 
multi-process application, as with `perf record -e '{....}:S'`. Instead 
users must use system-wide mode, or forgo the ability to sample counter 
groups. System-wide mode is often problematic as it requires specific 
permissions (no CAP_PERFMON / root access), or may lead to capture of 
significant amounts of extra data from other processes running on the 
system. 

Perf already supports the ability to collect per-thread counts with 
`inherit` via the `inherit_stat` flag. This patch changes 
`perf_event_alloc` relaxing the restriction to combine `inherit` with 
`PERF_SAMPLE_READ` so that the combination will be allowed so long as 
`inherit_stat` and `PERF_SAMPLE_TID` are enabled.

In this configuration stream ids (such as may appear in the read_format 
field of a PERF_RECORD_SAMPLE) are no longer globally unique, rather 
the pair of (stream id, tid) uniquely identify each event. Tools that 
rely on this, for example to calculate a delta between samples, would 
need updating to take this into account. Previously valid event 
configurations (system-wide, no-inherit and so on) where each stream id 
is the identifier are unaffected.

Changes since v2:
 - Rebase on v6.8
 - Respond to James Clarke's feedback; fixup some typos and move some
   repeated checks into a helper macro.
 - Cleaned up checkpatch lints.
 - Updated perf test; fixed evsel handling so that existing tests pass
   and added new tests to cover the new behaviour.

Changes since v1:
 - Rebase on v6.8-rc1
 - Fixed value written into sample after child exists.
 - Modified handling of switch-out so that context with these events
   take the slow path, so that the per-event/per-thread PMU state is
   correctly switched.
 - Modified perf tools to support this mode of operation.

Ben Gainey (4):
  perf: Support PERF_SAMPLE_READ with inherit_stat
  tools/perf: Track where perf_sample_ids need per-thread periods
  tools/perf: Correctly calculate sample period for inherited
    SAMPLE_READ values
  tools/perf: Allow inherit + inherit_stat + PERF_SAMPLE_READ when
    opening events

 include/linux/perf_event.h                    |  1 +
 kernel/events/core.c                          | 62 ++++++++++----
 tools/lib/perf/evlist.c                       |  1 +
 tools/lib/perf/evsel.c                        | 48 +++++++++++
 tools/lib/perf/include/internal/evsel.h       | 55 ++++++++++++-
 tools/perf/tests/attr/base-record             |  2 +-
 tools/perf/tests/attr/base-stat               |  2 +-
 tools/perf/tests/attr/system-wide-dummy       |  2 +-
 tools/perf/tests/attr/test-record-dummy-C0    |  2 +-
 .../test-record-group-sampling-inherit-stat   | 62 ++++++++++++++
 tools/perf/util/evsel.c                       | 82 ++++++++++++++++++-
 tools/perf/util/evsel.h                       |  1 +
 tools/perf/util/session.c                     | 11 ++-
 13 files changed, 305 insertions(+), 26 deletions(-)
 create mode 100644 tools/perf/tests/attr/test-record-group-sampling-inherit-stat

-- 
2.44.0