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Diffstat (limited to 'tools/perf/Documentation')
| -rw-r--r-- | tools/perf/Documentation/perf-list.txt | 107 |
1 files changed, 106 insertions, 1 deletions
diff --git a/tools/perf/Documentation/perf-list.txt b/tools/perf/Documentation/perf-list.txt index ec723d0a5bb3..a126e97a8114 100644 --- a/tools/perf/Documentation/perf-list.txt +++ b/tools/perf/Documentation/perf-list.txt @@ -93,6 +93,67 @@ 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/ ... + +PER SOCKET PMUS +--------------- + +Some PMUs are not associated with a core, but with a whole CPU socket. +Events on these PMUs generally cannot be sampled, but only counted globally +with perf stat -a. They can be bound to one logical CPU, but will measure +all the CPUs in the same socket. + +This example measures memory bandwidth every second +on the first memory controller on socket 0 of a Intel Xeon system + + perf stat -C 0 -a uncore_imc_0/cas_count_read/,uncore_imc_0/cas_count_write/ -I 1000 ... + +Each memory controller has its own PMU. Measuring the complete system +bandwidth would require specifying all imc PMUs (see perf list output), +and adding the values together. + +This example measures the combined core power every second + + perf stat -I 1000 -e power/energy-cores/ -a + +ACCESS RESTRICTIONS +------------------- + +For non root users generally only context switched PMU events are available. +This is normally only the events in the cpu PMU, the predefined events +like cycles and instructions and some software events. + +Other PMUs and global measurements are normally root only. +Some event qualifiers, such as "any", are also root only. + +This can be overriden by setting the kernel.perf_event_paranoid +sysctl to -1, which allows non root to use these events. + +For accessing trace point events perf needs to have read access to +/sys/kernel/debug/tracing, even when perf_event_paranoid is in a relaxed +setting. + +TRACING +------- + +Some PMUs control advanced hardware tracing capabilities, such as Intel PT, +that allows low overhead execution tracing. These are described in a separate +intel-pt.txt document. + PARAMETERIZED EVENTS -------------------- @@ -106,6 +167,50 @@ 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}' ... + +The number of available performance counters depend on the CPU. A group +cannot contain more events than available counters. +For example Intel Core CPUs typically have four generic performance counters +for the core, plus three fixed counters for instructions, cycles and +ref-cycles. Some special events have restrictions on which counter they +can schedule, and may not support multiple instances in a single group. +When too many events are specified in the group none of them will not +be measured. + +Globally pinned events can limit the number of counters available for +other groups. On x86 systems, the NMI watchdog pins a counter by default. +The nmi watchdog can be disabled as root with + + echo 0 > /proc/sys/kernel/nmi_watchdog + +Events from multiple different PMUs cannot be mixed in a group, with +some exceptions for software events. + +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 ------- @@ -143,5 +248,5 @@ SEE ALSO -------- linkperf:perf-stat[1], linkperf:perf-top[1], linkperf:perf-record[1], -http://www.intel.com/Assets/PDF/manual/253669.pdf[Intel® 64 and IA-32 Architectures Software Developer's Manual Volume 3B: System Programming Guide], +http://www.intel.com/sdm/[Intel® 64 and IA-32 Architectures Software Developer's Manual Volume 3B: System Programming Guide], http://support.amd.com/us/Processor_TechDocs/24593_APM_v2.pdf[AMD64 Architecture Programmer’s Manual Volume 2: System Programming] |