Messages in this thread Patch in this message | | | From | Andi Kleen <> | Subject | [PATCH 1/2] perf, tools: Document event specifications better | Date | Mon, 21 Mar 2016 08:56:32 -0700 |
| |
From: Andi Kleen <ak@linux.intel.com>
Document some undocumented features for specifying events in the perf list manpage:
- Event groups - Leader sampling - How to specify raw PMU events in the new syntax
Signed-off-by: Andi Kleen <ak@linux.intel.com> --- tools/perf/Documentation/perf-list.txt | 49 ++++++++++++++++++++++++++++++++++ 1 file changed, 49 insertions(+)
diff --git a/tools/perf/Documentation/perf-list.txt b/tools/perf/Documentation/perf-list.txt index 79483f4..240c8ff 100644 --- a/tools/perf/Documentation/perf-list.txt +++ b/tools/perf/Documentation/perf-list.txt @@ -91,6 +91,22 @@ raw encoding of 0x1A8 can be used: You should refer to the processor specific documentation for getting these details. Some of them are referenced in the SEE ALSO section below. +ARBITRARY PMUS +-------------- + +perf also supports an extended syntax for specifying raw parameters +to PMUs. Using this typically requires looking up the specific event +in the CPU vendor specific documentation. + +The available PMUs and their raw parameters can be listed with + + ls /sys/devices/*/format + +For example the raw event LSD.UOPS core pmu event above could +be specified as + + perf stat -e cpu/event=0xa8,umask=0x1,name=LSD.UOPS_CYCLES,cmask=1/ ... + PARAMETERIZED EVENTS -------------------- @@ -104,6 +120,39 @@ also be supplied. For example: perf stat -C 0 -e 'hv_gpci/dtbp_ptitc,phys_processor_idx=0x2/' ... +EVENT GROUPS +------------ + +Perf supports time based multiplexing of events, when the number of events +active exceeds the number of hardware performance counters. Multiplexing +can cause measurement errors when the workload changes its execution +profile. + +When metrics are computed using formulas from event counts, it is useful to +ensure some events are always measured together as a group to minimize multiplexing +errors. Event groups can be specified using { }. + + perf stat -e '{instructions,cycles}' ... + +When too many events are specified in the group perf the event will not +be measured. The number of available performance counters depend on the CPU. +For example Intel Core CPUs have typically four generic performance counters +for the core, plus a number of specialized fixed counters. + +Events from multiple different PMUs cannot be mixed in a group. + +LEADER SAMPLING +--------------- + +perf also supports group leader sampling using the :S specifier. + + perf record -e '{cycles,instructions}:S' ... + perf report --group + +Normally all events in a event group sample, but with :S only +the first event (the leader) samples, and it only reads the values of the +other events in the group. + OPTIONS ------- -- 2.5.5
| |