Questions tagged [perf]

From perf.wiki.kernel.org:

perf began as a tool for using the performance counters subsystem in Linux, and has had various enhancements to add tracing capabilities.

Performance counters are CPU hardware registers that count hardware events such as instructions executed, cache-misses suffered, or branches mispredicted. They form a basis for profiling applications to trace dynamic control flow and identify hotspots. perf provides rich generalized abstractions over hardware specific capabilities. Among others, it provides per task, per CPU and per-workload counters, sampling on top of these and source code event annotation.

Perf is natively supported in popular Linux distributions, including Red Hat Enterprise Linux and Debian (linux-tools package).

perf is used with several subcommands (short, non-exhaustive list):

• stat: runs a command and gather performance counter statistics;
• top: displays top-like dynamic view of hottest functions;
• record: runs a command and records its profile into perf.data;
• report: analyzes file generated by perf record; can generate flat, or graph profile;
• annotate: reads perf.data (created by perf record) and displays annotated code.

Example output of sudo perf stat tree /proc:

# started on Mon Aug 15 23:52:19 2016


 Performance counter stats for 'tree /proc':

       3929,205496 task-clock                #    0,681 CPUs utilized          
             79325 context-switches          #    0,020 M/sec                  
                33 CPU-migrations            #    0,000 M/sec                  
               273 page-faults               #    0,000 M/sec                  
        5745409809 cycles                    #    1,462 GHz                     [49,96%]
   <not supported> stalled-cycles-frontend 
   <not supported> stalled-cycles-backend  
        1465748665 instructions              #    0,26  insns per cycle         [74,84%]
         329884771 branches                  #   83,957 M/sec                   [75,30%]
          36420135 branch-misses             #   11,04% of all branches         [74,74%]

       5,765637169 seconds time elapsed