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29.2.2. Setting Events to Monitor
Most processors contain counters, which are used by OProfile to monitor specific events. As shown in Table 29.2, “OProfile Processors and Counters”, the number of counters available depends on the processor.
| Processor | cpu_type | Number of Counters |
|---|---|---|
| AMD64 | x86-64/hammer | 4 |
| AMD Athlon | i386/athlon | 4 |
| AMD Family 10h | x86-64/family10 | 4 |
| AMD Family 11h | x86-64/family11 | 4 |
| AMD Family 12h | x86-64/family12 | 4 |
| AMD Family 14h | x86-64/family14 | 4 |
| AMD Family 15h | x86-64/family15 | 6 |
| IBM eServer System i and IBM eServer System p | timer | 1 |
| IBM POWER4 | ppc64/power4 | 8 |
| IBM POWER5 | ppc64/power5 | 6 |
| IBM PowerPC 970 | ppc64/970 | 8 |
| IBM S/390 and IBM System z | timer | 1 |
| Intel Core i7 | i386/core_i7 | 4 |
| Intel Nehalem microarchitecture | i386/nehalem | 4 |
| Intel Pentium 4 (non-hyper-threaded) | i386/p4 | 8 |
| Intel Pentium 4 (hyper-threaded) | i386/p4-ht | 4 |
| Intel Westmere microarchitecture | i386/westmere | 4 |
| TIMER_INT | timer | 1 |
Use Table 29.2, “OProfile Processors and Counters” to verify that the correct processor type was detected and to determine the number of events that can be monitored simultaneously.
timer is used as the processor type if the processor does not have supported performance monitoring hardware.
If
timer is used, events cannot be set for any processor because the hardware does not have support for hardware performance counters. Instead, the timer interrupt is used for profiling.
If
timer is not used as the processor type, the events monitored can be changed, and counter 0 for the processor is set to a time-based event by default. If more than one counter exists on the processor, the counters other than counter 0 are not set to an event by default. The default events monitored are shown in Table 29.3, “Default Events”.
| Processor | Default Event for Counter | Description |
|---|---|---|
| AMD Athlon and AMD64 | CPU_CLK_UNHALTED | The processor's clock is not halted |
| AMD Family 10h, AMD Family 11h, AMD Family 12h | CPU_CLK_UNHALTED | The processor's clock is not halted |
| AMD Family 14h, AMD Family 15h | CPU_CLK_UNHALTED | The processor's clock is not halted |
| IBM POWER4 | CYCLES | Processor Cycles |
| IBM POWER5 | CYCLES | Processor Cycles |
| IBM PowerPC 970 | CYCLES | Processor Cycles |
| Intel Core i7 | CPU_CLK_UNHALTED | The processor's clock is not halted |
| Intel Nehalem microarchitecture | CPU_CLK_UNHALTED | The processor's clock is not halted |
| Intel Pentium 4 (hyper-threaded and non-hyper-threaded) | GLOBAL_POWER_EVENTS | The time during which the processor is not stopped |
| Intel Westmere microarchitecture | CPU_CLK_UNHALTED | The processor's clock is not halted |
| TIMER_INT | (none) | Sample for each timer interrupt |
The number of events that can be monitored at one time is determined by the number of counters for the processor. However, it is not a one-to-one correlation; on some processors, certain events must be mapped to specific counters. To determine the number of counters available, execute the following command:
~]# ls -d /dev/oprofile/[0-9]*
The events available vary depending on the processor type. To determine the events available for profiling, execute the following command as root (the list is specific to the system's processor type):
~]# ophelpNote
Unless OProfile is be properly configured, the
ophelp fails with the following error message:
Unable to open cpu_type file for reading Make sure you have done opcontrol --init cpu_type 'unset' is not valid you should upgrade oprofile or force the use of timer mode
To configure OProfile, follow the instructions in Section 29.2, “Configuring OProfile”.
The events for each counter can be configured via the command line or with a graphical interface. For more information on the graphical interface, see Section 29.9, “Graphical Interface”. If the counter cannot be set to a specific event, an error message is displayed.
To set the event for each configurable counter via the command line, use
opcontrol:
~]# opcontrol --event=event-name:sample-rate
Replace event-name with the exact name of the event from
ophelp, and replace sample-rate with the number of events between samples.
29.2.2.1. Sampling Rate
By default, a time-based event set is selected. It creates a sample every 100,000 clock cycles per processor. If the timer interrupt is used, the timer is set to whatever the jiffy rate is and is not user-settable. If the
cpu_type is not timer, each event can have a sampling rate set for it. The sampling rate is the number of events between each sample snapshot.
When setting the event for the counter, a sample rate can also be specified:
~]# opcontrol --event=event-name:sample-rate
Replace sample-rate with the number of events to wait before sampling again. The smaller the count, the more frequent the samples. For events that do not happen frequently, a lower count may be needed to capture the event instances.
Warning
Be extremely careful when setting sampling rates. Sampling too frequently can overload the system, causing the system to appear as if it is frozen or causing the system to actually freeze.
29.2.2.2. Unit Masks
Some user performance monitoring events may also require unit masks to further define the event.
Unit masks for each event are listed with the
ophelp command. The values for each unit mask are listed in hexadecimal format. To specify more than one unit mask, the hexadecimal values must be combined using a bitwise or operation.
~]# opcontrol --event=event-name:sample-rate:unit-mask