linux-kernel - Re: Announcing simple-pt -- a simple Processor Trace implementation for Linux

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Date:	Mon, 17 Aug 2015 15:09:33 +0200
From:	Frederic Weisbecker <fweisbec@...il.com>
To:	Andi Kleen <andi@...stfloor.org>
Cc:	LKML <linux-kernel@...r.kernel.org>,
	perf group <linux-perf-users@...r.kernel.org>
Subject: Re: Announcing simple-pt -- a simple Processor Trace implementation
 for Linux

2015-08-17 6:31 GMT+02:00 Andi Kleen <andi@...stfloor.org>:
>
> 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 “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

Nice. So I guess +x is the address offset. How hard would it be to
translate to file lines?

Thanks.

>         ...
>
> Available from https://github.com/andikleen/simple-pt
>
> --
> ak@...ux.intel.com -- Speaking for myself only.
> --
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