Messages in this thread | | | From | kan.liang@linux ... | Subject | [PATCH V2 0/5] Support metric group constraint | Date | Mon, 24 Feb 2020 13:59:19 -0800 |
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From: Kan Liang <kan.liang@linux.intel.com>
Changes since V1: - Remove global static flag violate_nmi_constraint, and add a new function metricgroup___watchdog_constraint_hint() for all watchdog constraint hints in patch 4. The rest of the patches are not changed.
Some metric groups, e.g. Page_Walks_Utilization, will never count when NMI watchdog is enabled.
$echo 1 > /proc/sys/kernel/nmi_watchdog $perf stat -M Page_Walks_Utilization
Performance counter stats for 'system wide':
<not counted> itlb_misses.walk_pending (0.00%) <not counted> dtlb_load_misses.walk_pending (0.00%) <not counted> dtlb_store_misses.walk_pending (0.00%) <not counted> ept.walk_pending (0.00%) <not counted> cycles (0.00%)
2.343460588 seconds time elapsed
Some events weren't counted. Try disabling the NMI watchdog: echo 0 > /proc/sys/kernel/nmi_watchdog perf stat ... echo 1 > /proc/sys/kernel/nmi_watchdog The events in group usually have to be from the same PMU. Try reorganizing the group.
A metric group is a weak group, which relies on group validation code in the kernel to determine whether to be opened as a group or a non-group. However, group validation code may return false-positives, especially when NMI watchdog is enabled. (The metric group is allowed as a group but will never be scheduled.)
The attempt to fix the group validation code has been rejected. https://lore.kernel.org/lkml/20200117091341.GX2827@hirez.programming.kicks-ass.net/ Because we cannot accurately predict whether the group can be scheduled as a group, only by checking current status.
This patch set provides another solution to mitigate the issue. Add "MetricConstraint" in event list, which provides a hint for perf tool, e.g. "MetricConstraint": "NO_NMI_WATCHDOG". Perf tool can change the metric group to non-group (standalone metrics) if NMI watchdog is enabled.
After applying the patch,
$echo 1 > /proc/sys/kernel/nmi_watchdog $perf stat -M Page_Walks_Utilization Splitting metric group Page_Walks_Utilization into standalone metrics. Try disabling the NMI watchdog to comply NO_NMI_WATCHDOG metric constraint: echo 0 > /proc/sys/kernel/nmi_watchdog perf stat ... echo 1 > /proc/sys/kernel/nmi_watchdog
Performance counter stats for 'system wide':
18,253,454 itlb_misses.walk_pending # 0.0 Page_Walks_Utilization (50.55%) 78,051,525 dtlb_load_misses.walk_pending (50.55%) 29,213,063 dtlb_store_misses.walk_pending (50.55%) 0 ept.walk_pending (50.55%) 2,542,132,364 cycles (49.92%)
1.037095993 seconds time elapsed
Kan Liang (5): perf jevents: Support metric constraint perf metricgroup: Factor out metricgroup__add_metric_weak_group() perf util: Factor out sysctl__nmi_watchdog_enabled() perf metricgroup: Support metric constraint perf vendor events: Add NO_NMI_WATCHDOG metric constraint
.../arch/x86/cascadelakex/clx-metrics.json | 3 +- .../pmu-events/arch/x86/skylake/skl-metrics.json | 3 +- .../pmu-events/arch/x86/skylakex/skx-metrics.json | 3 +- tools/perf/pmu-events/jevents.c | 19 ++-- tools/perf/pmu-events/jevents.h | 2 +- tools/perf/pmu-events/pmu-events.h | 1 + tools/perf/util/metricgroup.c | 109 ++++++++++++++++----- tools/perf/util/stat-display.c | 6 +- tools/perf/util/util.c | 18 ++++ tools/perf/util/util.h | 2 + 10 files changed, 128 insertions(+), 38 deletions(-)
-- 2.7.4
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