3. Specifying performance counter events

Whether profiling with operf or doing simple event counting with ocount, you can collect information about one more native hardware events using the --events option -- a comma-separated list of event specfications. The event specification is the means to provide details of how each hardware performance counter should be set up. For profiling, the event specification is a colon-separated string of the form name:count:unitmask:kernel:user as described in the table below. For ocount, specification is of the form name:unitmask:kernel:user. Note the presence of the count field for profiling. The count field tells the profiler how many events should occur between a profile snapshot (usually referred to as a "sample"). Since ocount does not do sampling, the count field is not needed.

If no event specs are passed to operf or ocount, the default event will be used.

Note

The perf_events kernel subsystem allocates hardware counters as necessary, but some processor types have restrictions as to what hardware events may be counted simultaneously. The kernel employs a multiplexing technique when such hardware restrictions are encountered, such that events are monitored on a rotating basis.

name The symbolic event name, e.g. CPU_CLK_UNHALTED
count The counter reset value, e.g. 100000; use only for profiling
unitmask The unit mask, as given in the events list: e.g. 0x0f; or a symbolic name if a name=<um_name> field is present
kernel Enable profiling of kernel code
user Enable profiling of userspace code

The last three values are optional; if you omit them (e.g. operf --events=DATA_MEM_REFS:30000), they will be set to the default values (i.e., the default unit mask value for the given event, and profiling (or counting) both kernel and userspace code will be enabled). Note that on some architectures, some events may require a unit mask be specified.

You can specify unit mask values using either a numerical value (hex values must begin with "0x") or a symbolic name (if the name=<um_name> field is shown in the ophelp output). For some named unit masks, the hex value is not unique; thus, OProfile tools enforce specifying such unit masks value by name.

The table below lists the default profiling event for various processor types. The same events can be used for ocount, minus the count field.

Processor cpu_type Default event
Alpha EV67 alpha/ev67 CYCLES:100000:0:1:1
ARM/XScale PMU1 arm/xscale1 CPU_CYCLES:100000:0:1:1
ARM/XScale PMU2 arm/xscale2 CPU_CYCLES:100000:0:1:1
ARM/MPCore arm/mpcore CPU_CYCLES:100000:0:1:1
Athlon i386/athlon CPU_CLK_UNHALTED:100000:0:1:1
Pentium Pro i386/ppro CPU_CLK_UNHALTED:100000:0:1:1
Pentium II i386/pii CPU_CLK_UNHALTED:100000:0:1:1
Pentium III i386/piii CPU_CLK_UNHALTED:100000:0:1:1
Pentium M (P6 core) i386/p6_mobile CPU_CLK_UNHALTED:100000:0:1:1
Pentium 4 (non-HT) i386/p4 GLOBAL_POWER_EVENTS:100000:1:1:1
Pentium 4 (HT) i386/p4-ht GLOBAL_POWER_EVENTS:100000:1:1:1
Hammer x86-64/hammer CPU_CLK_UNHALTED:100000:0:1:1
Family10h x86-64/family10 CPU_CLK_UNHALTED:100000:0:1:1
Family11h x86-64/family11h CPU_CLK_UNHALTED:100000:0:1:1
IBM pseries ppc64/power{ 4|5|6|7|8|970 } CYCLES:100000:0:1:1
IBM s390 s390/{ z10|z196|zEC12 } HWSAMPLING:4127518:0:1:1