Messages in this thread | | | Date | Wed, 26 Feb 2020 16:35:49 +0100 | From | Jiri Olsa <> | Subject | Re: [PATCH V2 0/5] Support metric group constraint |
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On Mon, Feb 24, 2020 at 01:59:19PM -0800, kan.liang@linux.intel.com wrote: > 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.
Acked-by: Jiri Olsa <jolsa@redhat.com>
thanks, jirka
> > 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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