...
1.0 | Use Linux perf interface to collect data about performance events on a per core basis | |||
2.0 | Use jevents library (PMU tools) | |||
3.0 | Should have a configurable interval | |||
4.0 | Should have configurable hardware specific events list | |||
5.0 | Provide SNMP support for any collectd values, through an PMU MIB | 6.0 | Provide support for multi PMU uncore events | |
| 76.0 | Provide option to choose all the events from json event list file |
...
The intel_pmu plugin collects information provided by Linux perf interface. It is not done directly, but through jevents API. Using this interface, the intel_pmu plugin collects the hardware specific metrics defined in event list file which should contain definitions of PMU events. The list of events to monitor is configurable.
Plugin configuration
The following configuration options should be supported by intel_pmu collectd plugin:
Name | Description | Comment |
Interval | The interval within which to retrieve statistics on monitored events in seconds | Interval option is supported by collectd and is defined in <LoadPlugin> block. No additional functionality should be developed in intel_pmu plugin to support this option. |
| EventList | Path to hardware events list file for current CPU. | File can be downloaded by event_download.py script which is part of pmu-tools package. |
HardwareEvents | String containing comma separated list of hardware specific events to monitor | "All" can be used to set all events from Event List. |
| Cores | Core groups definition. Monitored metrics are reported only for configured cores. If this option is omitted all available cores are monitored. If a group is enclosed in square brackets each core is added individually to a separate group (that is statistics are not aggregated). | Allowed formats: |
| DispatchMultiPmu | Enable/disable dispatching of cloned multi PMU for uncore events. If disabled only total sum is dispatched as single event. If enabled separate metric is dispatched for every counter. | Uncore event example: UNC_CHA_DIR_LOOKUP.NO_SNP. If enabled information about event type is added to type_instance, e.g.: "UNC_CHA_DIR_LOOKUP.NO_SNP:type=30". It allows to distinguish between multiple counters for one event. |
...
EventList "/var/cache/pmu/GenuineIntel-6-55-core.json"
HWSpecificEventsHardwareEvents "L2_RQSTS.CODE_RD_HIT,L2_RQSTS.CODE_RD_MISS" "L2_RQSTS.ALL_CODE_RD"
Cores ""
HardwareEvents "L2_RQSTS.PF_MISS"
Cores "1"
DispatchMultiPmu false
</Plugin>
In above example events L2_RQSTS.CODE_RD_HIT,L2_RQSTS.CODE_RD_MISS and L2_RQSTS.ALL_CODE_RD are going to be monitored on
all available cores, and event L2_RQSTS.PF_MISS is going to be monitored on core 1.
Another example with only uncore events set:
...
EventList "/var/cache/pmu/GenuineIntel-6-55-uncore.json"
HWSpecificEventsHardwareEvents "UNC_CHA_TOR_INSERTS.IA_MISS:config1=0x4043200000000" "UNC_IIO_TXN_REQ_BY_CPU.MEM_WRITE.PART0"
...
plugin API | jevents API | Description |
pmu_config | Parse events groups to monitor provided by user in collectd.conf | |
pmu_init | alloc_eventlist | Allocate memory for new eventlist |
resolve_event_extra | Resolve hardware specific events names to perf events (perf_event_attr) | |
jevent_pmu_uncore | Check if event is uncore event | |
jevent_next_pmu | Expand event into multiple PMU if neccessary (in use for uncore events) | |
setup_event | Setup perf events for monitoring | |
pmu_read | read_all_events | Read values of all monitored events |
pmu_shutdown | free_eventlist | Free memory allocated for eventlist (recursively including all events) |
...
For more details on plugin API see collectd plugin implementation guide https://collectd.org/wiki/index.php/Plugin_architecture.
Hardware Specific Events
In addition to standard groups of events supported by Linux perf (hardware cache, kernel pmu, software) The intel_pmu plugin allows to monitor hardware specific events. To support this functionality plugin will use feature provided by jevents library – resolving symbolic event names using downloaded event files. To be able to use hardware specific event names in configuration file user will have to download events list file for current CPU before using intel_pmu plugin. This can be done using event_download.py script which is part of pmu-tools package.
Note: For uncore events values can be collected only for first core of every socket e.g. '0' '18' etc.
Time based multiplexing
If there are more events than counters, the kernel uses time multiplexing to give each event a chance to access the monitoring hardware. With multiplexing, an event is not measured all the time. At the end of the run, the tool scales the count based on total time enabled vs time running. The actual formula is:
scaledcount = rawcount * timeenabled / timerunning
This provides an estimate of what the count would have been, had the event been measured during the entire run. Note that this is an estimate not an actual count. Depending on the workload, there will be blind spots which can introduce errors during scaling.
The plugin dispatches all the four values, that is scaled, raw, time enabled & running, to the user. The values type is COUNTER.
SNMP Support
All metrics collected by intel_pmu plugin should be available through SNMP. This will be achieved by creating proper configuration for snmp_agent collectd plugin. No additional functionality needed in intel_pmu plugin to support SNMP. See description of SNMP feature for more details on snmp_agent plugin.
...
Configuration Considerations
When using intel_pmu plugin number of reading threads in collectd should be increased. The value should be more than a half of configured cores, so for
60 monitored cores the recommendation is to set ReadThreads > 30 (e.g. 35).
Deployment Considerations
...
The Tests should be carried out on a system underload under load as well as a relatively idle system.
...
Ref | Dependency | Status |
1 | libjevents | |
2Net-SNMP | ||
3 | ||
4 |