Announcing simple-pt -- a simple Processor Trace implementation for Linux

From: Andi Kleen
Date: Mon Aug 17 2015 - 00:32:02 EST



Modern Intel Core CPUs (5th and 6th generation) have a Intel Processor Trace (PT) feature
to trace branch execution with low overhead. This is useful for performance analysis and debugging.

simple-pt is a simple standalone driver and decoder tool to implement PT on Linux.

Starting with Linux 4.1 Linux has an integrated PT implementation in perf
(see https://lwn.net/Articles/648154/).
simple-pt is an alternative implementation. It has many disadvantages over the perf PT
implementation, such as:
- needs to run as root
- no long term tracing or sampling with interrupts
- no support for interactive debugging (use gdb 7.10 on perf for that)
- no support for histograms
- somewhat experimental
- not as well supported as perf

On the positive side simple-pt is:
- simple
- standalone. No kernel changes needed. Could be ported to older kernels or other operating systems
- easy to modify and experiment with
- more ftrace like decoding tool
- support for kprobes based triggers
- modular âunix styleâ design with simple tools that do only one thing each
- BSD licensed

Example output:


% sptcmd -c tcall taskset -c 0 ./tcall
cpu 0 offset 1027688, 1003 KB, writing to ptout.0
...
Wrote sideband to ptout.sideband
% sptdecode --sideband ptout.sideband --pt ptout.0 | less
TIME DELTA INSNs OPERATION
frequency 32
0 [+0] [+ 1] _dl_aux_init+436
[+ 6] __libc_start_main+455 -> _dl_discover_osversion
...
[+ 13] __libc_start_main+446 -> main
[+ 9] main+22 -> f1
[+ 4] f1+9 -> f2
[+ 2] f1+19 -> f2
[+ 5] main+22 -> f1
[+ 4] f1+9 -> f2
[+ 2] f1+19 -> f2
[+ 5] main+22 -> f1
...

Available from https://github.com/andikleen/simple-pt

--
ak@xxxxxxxxxxxxxxx -- Speaking for myself only.
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