Bug#911815: /usr/bin/perf_4.18: Please build perf against libbfd

[Mike Hommey <mh@glandium.org>]

On Thu, Oct 25, 2018 at 03:20:11PM +0900, Mike Hommey wrote:
> Package: linux-perf-4.18
> Version: 4.18.10-2
> Severity: wishlist
> File: /usr/bin/perf_4.18
> 
> Dear Maintainer,
> 
> Running e.g. perf report with dwarf call graph info can take a long time
> depending on the size of the profile and the size of dwarf info in the
> binaries being profiled. That's because each address in each library is
> handled by forking and executing a new addr2line process. Each addr2line
> process has to parse the dwarf info of the library it's given just to
> find the location of one address. Multiply by the number of addresses,
> and this can quickly become ridiculous.
> 
> Perf, however, has an alternative implementation that just uses libbfd,
> so it would be much faster than spawning a large amount of new
> processes, each with a large overhead.

I found https://salsa.debian.org/kernel-team/linux/blob/master/debian/rules.d/tools/perf/Makefile#L27-31

This sucks badly :(
I have some massive perf data that take *hours* to deal with without
libbfd. With a reduced perf data, this is the kind of difference this
makes:

$ time perf script > /dev/null   # addr2line
real    3m8.718s
user    1m12.606s
sys     1m56.649s

$ time perf script > /dev/null   # libbfd
real    0m4.141s
user    0m3.425s
sys     0m0.894s

Mike