linux-kernel - [RFCv4 0/7] arm_pmu/perf tools: play nicely with CPU PMU cpumasks

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Date:   Thu,  8 Sep 2016 11:21:45 +0100
From:   Mark Rutland <mark.rutland@....com>
To:     linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org
Cc:     acme@...nel.org, alexander.shishkin@...ux.intel.com,
        jolsa@...nel.org, mark.rutland@....com, mingo@...hat.com,
        peterz@...radead.org, will.deacon@....com
Subject: [RFCv4 0/7]  arm_pmu/perf tools: play nicely with CPU PMU cpumasks

Hi,

I'm trying to make the perf tool play better with PMUs in heterogeneous systems
(e.g. big.LITTLE), where there are several logical PMUs, each covering a subset
of CPUs.

Currently perf-record doesn't work for these PMUs, unless forced to use
per-thread mmaps. In the absence of a cpumask, it tries to open events on CPUs
not supported by a PMU, and gives up. In the presence of a cpumask, it ends up
failing to mmap, as the evlist->cpus map contains a different set of CPUs from
the evsel->cpus map populated from the cpumask. This is addressed by the
penultimate patch in this series.

Complicating matters, prior to commit 00e727bb389359c8 ("perf stat: Balance
opening and reading events"), from version two of this series, perf-stat would
behave erroneously in the presence of a cpumask file, blocking forever after
the workload completed. While this is now fixed, existing binaries (e.g. those
shipped by distributions) would be broken by the addition of a cpumask file
kernel-side.

To cater for this, this series adds support for a new PMU sysfs file, named
'cpus' rather than 'cpumask', listing a number of CPUs that a logical PMU
covers. As old binaries will not look for this, this can be safely added to the
kernel without risk of breakage.

I've included the kernel and userspace parts in this series as they've proven
difficult to review in isolation.

Thanks,
Mark.

Since v1 [1]:
* Avoid double cpu_map__idx() call in perf_evlist__mmap_per_evsel
* Look for a supported_cpumask file when a cpumask file is not present

Since v2 [2]:
* Drop patches which have been picked up from v2
* Rebase to v4.8-rc1
* Better describe the issue in the supported_cpumask patch

Since v3 [3]:
* Prepend patches exporting the cpus file for ARM PMUs
* s/supported_cpus/cpus/

[1] http://lkml.kernel.org/r/1467907474-3290-1-git-send-email-mark.rutland@arm.com
[2] http://lkml.kernel.org/r/1468577293-19667-1-git-send-email-mark.rutland@arm.com
[3] http://lkml.kernel.org/r/1470933366-1364-1-git-send-email-mark.rutland@arm.com

Mark Rutland (7):
  drivers/perf: arm_pmu: add common attr group fields
  arm64: perf: move to common attr_group fields
  arm: perf: move to common attr_group fields
  drivers/perf: arm_pmu: only use common attr_groups
  drivers/perf: arm_pmu: expose a cpumask in sysfs
  perf: util: only open events on CPUs an evsel permits
  perf: util: support alternative sysfs cpumask

 arch/arm/kernel/perf_event_v7.c | 47 ++++++++++++++++++++++++-----------------
 arch/arm64/kernel/perf_event.c  | 36 ++++++++++++++++++++-----------
 drivers/perf/arm_pmu.c          | 23 ++++++++++++++++++++
 include/linux/perf/arm_pmu.h    | 10 ++++++++-
 tools/perf/util/evlist.c        |  8 ++++++-
 tools/perf/util/pmu.c           | 15 ++++++++++---
 6 files changed, 103 insertions(+), 36 deletions(-)

-- 
1.9.1