Announcing simple-pt — A simple Processor Trace implementation
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 already has a 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 “unix style” 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