Hardware Counter Lists

Hardware counters are processor-specific, so the choice of counters available to you depends on the processor that you are using. The performance tools provide aliases for a number of counters that are likely to be in common use. You can obtain a list of available hardware counters on any particular system from the Collector by typing collect with no arguments in a terminal window on that system. If the processor and system support hardware counter profiling, the collect command prints two lists containing information about hardware counters. The first list contains hardware counters that are aliased to common names; the second list contains raw hardware counters. If neither the performance counter subsystem nor the collect command know the names for the counters on a specific system, the lists are empty. In most cases, however, the counters can be specified numerically.

Here is an example that shows the entries in the counter list. The counters that are aliased are displayed first in the list, followed by a list of the raw hardware counters. Each line of output in this example is formatted for print.

Aliased HW counters available for profiling:
cycles[/{0|1}],9999991 (’CPU Cycles’, alias for Cycle_cnt; CPU-cycles)
insts[/{0|1}],9999991 (’Instructions Executed’, alias for Instr_cnt; events)
dcrm[/1],100003 (’D$ Read Misses’, alias for DC_rd_miss; load events)
...
Raw HW counters available for profiling:
Cycle_cnt[/{0|1}],1000003 (CPU-cycles)
Instr_cnt[/{0|1}],1000003 (events)
DC_rd[/0],1000003 (load events)

Format of the Aliased Hardware Counter List

In the aliased hardware counter list, the first field (for example, cycles) gives the alias name that can be used in the -h counter... argument of the collect command. This alias name is also the identifier to use in the er_print command.

The second field lists the available registers for the counter; for example, [/{0|1}].

The third field, for example, 9999991, is the default overflow value for the counter. For aliased counters, the default value has been chosen to provide a reasonable sample rate. Because actual rates vary considerably, you might need to specify a non-default value.

The fourth field, in parentheses, contains type information. It provides a short description (for example, CPU Cycles), the raw hardware counter name (for example, Cycle_cnt), and the type of units being counted (for example, CPU-cycles).

If the first word of type information is:

• load, store, or load-store, the counter is memory-related. You can prepend a + sign to the counter name (for example, +dcrm) in the collect -h command, to request a search for the precise instruction and virtual address that caused the event. The + sign also enables dataspace profiling; see The DataObjects Tab, The DataLayout Tab, and The MemoryObjects Tabs for details.

• not-program-related, the counter captures events initiated by some other program, such as CPU-to-CPU cache snoops. Using the counter for profiling generates a warning and profiling does not record a call stack.

If the second or only word of the type information is:

• CPU-cycles, the counter can be used to provide a time-based metric. The metrics reported for such counters are converted by default to inclusive and exclusive times, but can optionally be shown as event counts.

• events, the metric is inclusive and exclusive event counts, and cannot be converted to a time.

In the aliased hardware counter list in the example, the type information contains one word, CPU-cycles for the first counter and events for the second counter. For the third counter, the type information contains two words, load events.

Format of the Raw Hardware Counter List

The information included in the raw hardware counter list is a subset of the information in the aliased hardware counter list. Each line in the raw hardware counter list includes the internal counter name as used by cpu-track(1), the register numbers on which that counter can be used, the default overflow value, and the counter units, which can be either CPU-cycles or Events.

If the counter measures events unrelated to the program running, the first word of type information is not-program-related. For such a counter, profiling does not record a call stack, but instead shows the time being spent in an artificial function, collector_not_program_related . Thread and LWP ID’s are recorded, but are meaningless.

The default overflow value for raw counters is 1000003. This value is not ideal for most raw counters, so you should specify overflow values when specifying raw counters.