[PATCH] pmcannotate tool

Ray Kinsella raykinsella78 at gmail.com
Sun Nov 23 12:26:30 PST 2008

I know I am going to really show my FreeBSD ignorance here, but this is a
patch of FreeBSD 8.0 Current isn't it ?


Ray Kinsella

On Sun, Nov 23, 2008 at 1:02 PM, Attilio Rao <attilio at freebsd.org> wrote:

> pmcannotate is a tool that prints out sources of a tool (in C or
> assembly) with inlined profiling informations retrieved by a prior
> pmcstat analysis.
> If compared with things like callgraph generation, it prints out
> profiling on a per-instance basis and this can be useful to find, for
> example, badly handled caches, too high latency instructions, etc.
> The tool usage is pretty simple:
> pmcannotate [-a] [-h] [-k path] [-l level] samples.out binaryobj
> where samples.out is a pmcstat raw output and binaryobj is the binary
> object that has been profiled and is accessible for (ELF) symbols
> retrieving.
> The options are better described in manpages but briefly:
> - a: performs analysis on the assembly rather than the C source
> - h: usage and informations
> - k: specify a path for the kernel in order to locate correct objects for
> it
> - l: specify a lower boundary (in total percentage time) after which
> functions will be displayed nomore.
> A typical usage of pmcannotate can be some way of kernel annotation.
> For example, you can follow the steps below:
> 1) Generate a pmc raw output of system samples:
> # pmcstat -S ipm-unhalted-core-cycles -O samples.out
> 2) Copy the samples in the kernel building dir and cd there
> # cp samples.out /usr/src/sys/i386/compile/GENERIC/ ; cd
> /usr/src/sys/i386/compile/GENERIC/
> 3) Run pmcannotate
> # pmcannotate -k . samples.out kernel.debug > kernel.ann
> In the example above please note that kernel.debug has to be used in
> order to produce a C annotated source. This happens because in order
> to get the binary sources we rely on the "objdump -S" command which
> wants binary compiled with debugging options.
> If not debugging options are present assembly analynsis is still
> possible, but no C-backed one will be available.
> objdump is not the only one tool on which pmcannotare rely. Infact, in
> order to have it working, pmcstat needs to be present too because we
> need to retrieve, from the pmcstat raw output, informations about the
> sampled PCs (in particular the name of the function they live within,
> its start and ending addresses). As long as currently pmcstat doesn't
> return those informations, a new option has been added to the tool
> (-m) which can extract (from a raw pmcstat output) all pc sampled,
> name of the functions and symbol bundaries they live within.
> Also please note that pmcannotate suffers of 2 limitations.
> Firstly, relying on objdump to dump the C source, with heavy
> optimization levels and lots of inlines the code gets difficult to
> read. Secondly, in particular on x86 but I guess it is not the only
> one case, the sample is always attributed to the instruction directly
> following the one that was interrupted. So in a C source view some
> samples may be attributed to the line below the one you're interested
> in.  It's also important to keep in mind that if a line is a jump
> target or the start of a function the sample really belongs elsewhere.
> The patch can be found here:
> http://www.freebsd.org/~attilio/pmcannotate.diff/<http://www.freebsd.org/%7Eattilio/pmcannotate.diff/>
> where pmcannotate/ dir contains the code and needs to go under
> /usr/src/usr.sbin/ and the patch has diffs against pmcstat and
> Makefile.
> This work has been developed on the behalf of Nokia with important
> feedbacks and directions from Jeff Roberson.
> Testing and feedbacks (before it hits the tree) are welcome.
> Thanks,
> Attilio
> --
> Peace can only be achieved by understanding - A. Einstein
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