perf - What is perf?
- The generic profiler tool for linux
- Provides a rich set of tools that abstracts away CPU hardware differences
- Is available in all modern linux systems
perf - allows you to trace, collect and analyze data
- perf is available in linux-tools-common package
-
perf supports a rich set of commands. Just type ‘perf’..
annotate Read perf.data (created by perf record) and display annotated code list List all symbolic event types record Run a command and record its profile into perf.data report Read perf.data (created by perf record) and display the profile sched Tool to trace/measure scheduler properties (latencies) script Read perf.data (created by perf record) and display trace output stat Run a command and gather performance counter statistics timechart Tool to visualize total system behavior during a workload top System profiling tool.
perf - Sample usage
-
In it’s simplest form:
perf record -a -g -F 99 –
- This records the activity in the system by:
- -F sampling at a sampling frequency of 99Hz
- -a profiling all cores
- -g generating call graph info
-
Now for generating human readable output from the collected traces
perf report
- This displays the performance counter profile info recorded earlier
perf report
+ 27.12% chrome chrome [.] 0x00000000029633cb
+ 5.18% chrome [kernel.kallsyms] [k] trace_graph_entry
+ 2.67% chrome perf-21360.map [.] 0x000018b2828b9a40
+ 2.54% byobu-status [kernel.kallsyms] [k] trace_graph_entry
+ 2.38% swapper [kernel.kallsyms] [k] intel_idle
+ 1.86% swapper [kernel.kallsyms] [k] trace_graph_entry
+ 1.45% Xorg [kernel.kallsyms] [k] trace_graph_entry
+ 1.42% vpnagentd [kernel.kallsyms] [k] trace_graph_entry
+ 1.38% chrome [kernel.kallsyms] [k] prepare_ftrace_return
+ 1.38% sh [kernel.kallsyms] [k] trace_graph_entry
Output of perf report -n –stdio
perf report -n –stdio
# Samples: 556 of event 'cycles'
# Event count (approx.): 6711822878
#
# Overhead Samples Command Shared Object
# ........ ............ .......... ..................
#
27.12% 115 chrome chrome [.] 0x00000000029633cb
|
|
...
5.18% 22 chrome [kernel.kallsyms] [k] trace_graph_entry
|
--- trace_graph_entry
prepare_ftrace_return
ftrace_graph_caller
|
|
...
2.54% 12 byobu-status [kernel.kallsyms] [k] trace_graph_entry
|
--- trace_graph_entry
|
|
Ouput of perf top
perf top
PerfTop: 2852 irqs/sec kernel:74.9% exact: 0.0% [4000Hz cycles], (all, 4 CPUs)
----------------------------------------------------------------------------------------
14.81% [kernel] [k] arch_cpu_idle
3.76% [unknown] [.] 0x76e22324
1.90% [kernel] [k] __memzero
1.27% [unknown] [.] 0x76e21960
1.19% [kernel] [k] finish_task_switch
1.16% [kernel] [k] _raw_spin_unlock_irqrestore
1.01% [unknown] [.] 0x76e22320
0.98% [kernel] [k] rcu_idle_exit
0.92% [unknown] [.] 0x76e21958
0.86% [kernel] [k] copy_page
0.72% [unknown] [.] 0x76e21954
0.71% [kernel] [k] filemap_map_pages
0.67% [kernel] [k] get_page_from_freelist
0.57% [kernel] [k] do_page_fault
0.51% [kernel] [k] handle_mm_fault
0.49% [kernel] [k] unmap_single_vma
0.37% [unknown] [.] 0x76ded280
0.35% [kernel] [k] __wake_up_bit
0.34% [kernel] [k] free_hot_cold_page
0.34% [kernel] [k] memcpy
0.31% [kernel] [k] __usb_hcd_giveback_urb
0.31% [kernel] [k] vector_swi
0.30% [kernel] [k] __sync_icache_dcache
0.28% [kernel] [k] __do_softirq
....
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