Before OProfile can be run, it must be configured. At a minimum,
selecting to monitor the kernel (or selecting not to monitor the
kernel) is required. The following sections describe how to use the
opcontrol utility to configure OProfile.
As the opcontrol commands are executed,
the setup options are saved to the /root/.oprofile/daemonrc file.
First, configure whether OProfile should monitor the kernel.
This is the only configuration option that is required before
starting OProfile. All others are optional.
To monitor the kernel, execute the following command as
root:
opcontrol --setup --vmlinux=/usr/lib/debug/lib/modules/`uname -r`/vmlinux
|
 |
Note |
| |
The debuginfo package must be installed
(which contains the uncompressed kernel) in order to monitor the
kernel.
|
To configure OProfile not to monitor the kernel, execute the
following command as root:
opcontrol --setup --no-vmlinux
|
This command also loads the oprofile kernel module, if it is not
already loaded, and creates the /dev/oprofile/ directory, if it does not already
exist. Refer to Section
41.6 Understanding /dev/oprofile/ for details about this
directory.
|
Note |
| |
Even if OProfile is configured not to profile the kernel, the
SMP kernel still must be running so that the oprofile module can be loaded from it.
|
Setting whether samples should be collected within the kernel
only changes what data is collected, not how or where the collected
data is stored. To generate different sample files for the kernel
and application libraries, refer to Section
41.2.3 Separating Kernel and User-space Profiles.
Most processors contain counters, which
are used by OProfile to monitor specific events. As shown in
Table
41-2, the number of counters available depends on the
processor.
| Processor |
cpu_type |
Number of Counters |
| Pentium Pro |
i386/ppro |
2 |
| Pentium II |
i386/pii |
2 |
| Pentium III |
i386/piii |
2 |
| Pentium 4 (non-hyper-threaded) |
i386/p4 |
8 |
| Pentium 4 (hyper-threaded) |
i386/p4-ht |
4 |
| Athlon |
i386/athlon |
4 |
| AMD64 |
x86-64/hammer |
4 |
| Itanium |
ia64/itanium |
4 |
| Itanium 2 |
ia64/itanium2 |
4 |
| TIMER_INT |
timer |
1 |
| IBM eServer iSeries and pSeries |
timer |
1 |
| |
ppc64/power4 |
8 |
| |
ppc64/power5 |
6 |
| |
ppc64/970 |
8 |
| IBM eServer S/390 and S/390x |
timer |
1 |
| IBM eServer zSeries |
timer |
1 |
Table 41-2. OProfile Processors and Counters
Use Table
41-2 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
41-3.
| Processor |
Default Event for Counter |
Description |
| Pentium Pro, Pentium II, Pentium III, Athlon, AMD64 |
CPU_CLK_UNHALTED |
The processor's clock is not halted |
| Pentium 4 (HT and non-HT) |
GLOBAL_POWER_EVENTS |
The time during which the processor is not stopped |
| Itanium 2 |
CPU_CYCLES |
CPU Cycles |
| TIMER_INT |
(none) |
Sample for each timer interrupt |
| ppc64/power4 |
CYCLES |
Processor Cycles |
| ppc64/power5 |
CYCLES |
Processor Cycles |
| ppc64/970 |
CYCLES |
Processor Cycles |
Table 41-3. Default Events
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:
cat /dev/oprofile/cpu_type
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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):
The events for each counter can be configured via the command
line or with a graphical interface. For more information on the
graphical interface, refer to Section 41.8 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 op_help,
and replace <sample-rate> with
the number of events between samples.
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.
 |
Caution |
| |
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.
|
If the cpu_type is not
timer, unit masks may also be required to further define
the event.
Unit masks for each event are listed with the op_help 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>
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By default, kernel mode and user mode information is gathered
for each event. To configure OProfile not to count events in kernel
mode for a specific counter, execute the following command:
opcontrol --event=<event-name>:<sample-rate>:<unit-mask>:0
|
Execute the following command to start profiling kernel mode for
the counter again:
opcontrol --event=<event-name>:<sample-rate>:<unit-mask>:1
|
To configure OProfile not to count events in user mode for a
specific counter, execute the following command:
opcontrol --event=<event-name>:<sample-rate>:<unit-mask>:<kernel>:0
|
Execute the following command to start profiling user mode for
the counter again:
opcontrol --event=<event-name>:<sample-rate>:<unit-mask>:<kernel>:1
|
When the OProfile daemon writes the profile data to sample
files, it can separate the kernel and library profile data into
separate sample files. To configure how the daemon writes to sample
files, execute the following command as root:
opcontrol --separate=<choice>
|
<choice> can be one of the
following:
-
none — do not separate
the profiles (default)
-
library — generate
per-application profiles for libraries
-
kernel — generate per-application
profiles for the kernel and kernel modules
-
all — generate per-application
profiles for libraries and per-application profiles for the kernel
and kernel modules
If --separate=library is used, the
sample file name includes the name of the executable as well as the
name of the library.
