• sources
• Quick ref
• Concepts
• Code path:
• How it works
• ftrace event tracing
• Top-down analysis
• MISC::tooltips
• MISC::How does perf work
• MISC::TPEBS (Intel)
• MISC::TRIVIAS

# sources

• https://perfwiki.github.io/main/

# Quick ref

Listing supported events:

$ perf list

Manually tackling ftrace:

# set trace points for kmalloc
$ echo kmalloc > /sys/kernel/debug/tracing/set_event
$ cat /sys/kernel/debug/tracing/trace

# Concepts

top-down analysis

https://ieeexplore.ieee.org/document/6844459/

perf Events

• HW events / HW cache events: events measured by processor’s PMU.
• Software Events: events measurable by kernel counter. (e.g. cpu-clock, page-faults)
• tracepoint events: code locations built into the kernel to collect trace information
• probe events: user-defined events dynamically inserted into the kernel

# Code path:

Slides Perf for User Space Program Analysis, Tetsuo Takata, NTT DATA CORP.

perf_event_open API
userspace commands are commited via perf_event_open syscall, which may

• register sw event handler.
• enable ftrace events.
• enable kprobes
• configure PMU (hardware Performance Monitor Units)

Sampling
perf module collects samples what about user space function tracing?) when an event occurs. Collected data includes {IP, user/kernel stack, timer, HW stuffs}. The collected data are written to a dedicated perf buffer to avoid kernel-to-user copying.

The triggering events could be HW event, interrupt/exception event (timer irq, page fault..) or kernel SW event (context switch, cpu migration..)

# How it works

https://alex.dzyoba.com/blog/perf/

# ftrace event tracing

https://alex.dzyoba.com/blog/ftrace/

ftrace provides lockless ringbuffer framework; tracers builds the actual tracings

• function - default tracer
• function_graph
• latency tracers: {irqsoff, preempoff, preemptirqsoff, wakeup etc.}
• additional features: kernel tracepoints, kprobes, blktrace ..

function tracing

events tracing

kprobes tracing

# Top-down analysis

# MISC::tooltips

perf privileges / permissions

# MISC::How does perf work

# MISC::TPEBS (Intel)

• TPEBS: Timed Process Event Based Sampling¹
• TMA: Top-down Microarchitecture Analysis

# MISC::TRIVIAS

there are tools built upon the same kernel perf support: {perf, oprofile, gprof, sysprof}. Perf is the most versatile and most relevant one.