User guide

Perf Tool Commands

switches. For example, PCL counters can compute the Instructions Per Clock (IPC) from a process's

counts of instructions retired and processor clock cycles. A low IPC ratio indicates the code makes

poor use of the CPU. Other hardware events can also be used to diagnose poor CPU performance.

Performance counters can also be configured to record samples. The relative frequency of samples

can be used to identify which regions of code have the greatest impact on performance.

6.6.1. Perf Tool Commands

Useful perf commands include the following:

perf stat

This perf command provides overall statistics for common performance events, including

instructions executed and clock cycles consumed. Options allow selection of events other than the

default measurement events.

perf record

This perf command records performance data into a file which can be later analyzed using perf

report.

perf report

This perf command reads the performance data from a file and analyzes the recorded data.

perf list

This perf command lists the events available on a particular machine. These events will vary

based on the performance monitoring hardware and the software configuration of the system.

Use perf help to obtain a complete list of perf commands. To retrieve man page information on

each perf command, use perf help command.

6.6.2. Using Perf

Using the basic PCL infrastructure for collecting statistics or samples of program execution is relatively

straightforward. This section provides simple examples of overall statistics and sampling.

To collect statistics on make and its children, use the following command:

perf stat -- make all

The perf command will collect a number of different hardware and software counters. It will then print

the following information:

Performance counter stats for 'make all':

244011.782059 task-clock-msecs # 0.925 CPUs

53328 context-switches # 0.000 M/sec

515 CPU-migrations # 0.000 M/sec

1843121 page-faults # 0.008 M/sec

789702529782 cycles # 3236.330 M/sec

1050912611378 instructions # 1.331 IPC

275538938708 branches # 1129.203 M/sec

2888756216 branch-misses # 1.048 %

4343060367 cache-references # 17.799 M/sec

428257037 cache-misses # 1.755 M/sec

263.779192511 seconds time elapsed