Comparison between perf, Ftrace, LTTng and GDB tracepoints Rafik - PowerPoint PPT Presentation

Comparison between perf, Ftrace, LTTng and GDB tracepoints Rafik Fahem Department of Computer and Software Engineering June 29, 2010 École Polytechnique, Montreal 1

Content Perf Ftrace LTTng GDB tracepoints Discussion Questions Comparison between perf, Ftrace, LTTng and GDB tracepoints 2 2

Perf ● Used for performance analysis ● Static tracepoints: ● Makes use of the tracepoints available in the kernel(version 2.6.32 and higher) ● Dynamic tracepoints can be defined with: ● Symbols and registers without debuginfo ● C line numbers, function names and local variables with debuginfo Comparison between perf, Ftrace, LTTng and GDB tracepoints 3 3

Perf ● Dynamic tracepoints are implemented with kprobes ● Vmlinux containing the debuginfo has to be a Dwarf binary ● Traces only the events generated by a specific program Comparison between perf, Ftrace, LTTng and GDB tracepoints 4 4

Perf ● Available data: ● Number of times the tracepoint was hit ● Execution time ● Calling functions ● Trace is available only after execution Comparison between perf, Ftrace, LTTng and GDB tracepoints 5 5

Ftrace ● Can be used for debugging and latency analysis ● Includes six different tracers: function calls, context switches...etc ● Uses the static tracepoints available in the kernel source ● Dynamic tracepoints unavailable Comparison between perf, Ftrace, LTTng and GDB tracepoints 6 6

Ftrace ● Available data depends on the tracer enabled: execution time, calling functions, PIDs... ● Thousands of filters available to trace only some selected events ● Trace is recorded in debugfs ● Trace can be viewed when tracing Comparison between perf, Ftrace, LTTng and GDB tracepoints 7 7

LTTng ● Optimized for static tracing ● Uses the static tracepoints available in the kernel ● Dynamic tracepoints implemented using kprobes ● Several probes can be connected to the same tracepoint ● Live monitoring under development Comparison between perf, Ftrace, LTTng and GDB tracepoints 8 8

GDB tracepoints ● Can only be used in user space ● Only dynamic tracepoints are supported in the current version ● UST tracepoints can be used ● Tracepoints inserted using traps ● Fast tracepoints: ● Faster but restricted in where they may be installed ● Inserted with a jump Comparison between perf, Ftrace, LTTng and GDB tracepoints 9 9

GDB tracepoints ● Data collected can include registers, local variables and global data. ● Tracepoints can be defined with line numbers, function names and addresses ● A trace snapshot is collected every time a tracepoint is hit ● These snapshots are stored in buffers and can be examined later Comparison between perf, Ftrace, LTTng and GDB tracepoints 10 10

Discussion ● Perf: ● Tracing a single program ● Statistics: execution time, calling functions, number of times the tracepoint was hit ● Hardware performance counters ● Ftrace: ● Filters ● Trace in debugfs Comparison between perf, Ftrace, LTTng and GDB tracepoints 11 11

Discussion ● LTTng: ● Optimized static tracing ● User-space tracing ● Trace streaming ● GDB tracepoints: ● Fast tracepoints using jumps ● Debuginfo is needed to access variables(SystemTap) Comparison between perf, Ftrace, LTTng and GDB tracepoints 12 12

Questions? Comparison between perf, Ftrace, LTTng and GDB tracepoints 13 13