Re: [PATCH] Enhance perf to collect KVM guest os statistics from host side

[Arnaldo Carvalho de Melo <acme@infradead.org>]

Em Tue, Mar 23, 2010 at 03:20:11PM +0100, Andi Kleen escreveu:
> Soeren Sandmann <sandmann@daimi.au.dk> writes:
> > I don't think the oprofile JIT interface solves any of these
> > problems. (In fact, I don't see why the JIT problem is even hard. The
> > JIT compiler can just generate a little ELF file with symbols in it,
> > and the profiler can pick it up through the mmap events that you get
> > through the perf interface).
> 
> That would require keeping those temporary ELF files for
> potentially unlimited time around (profilers today look at the ELF
> files at the final analysis phase, which might be weeks away)

'perf record' will traverse the perf.data file just collected and, if the
binaries have build-ids, will stash them in ~/.debug/, keyed by build-id
just like the -debuginfo packages do.

So only the binaries with hits. Also one can use 'perf archive' to
create a tar.bz2 file with the files with hits for the specified
perf.data file, that can then be transfered to another machine, whatever
arch, untarred at ~/.debug and then the report can be done there.

As it is done by build-id, multiple 'perf record' sessions share files
in the cache.

Right now the whole ELF file (or /proc/kallsyms copy) is stored if
collected from the DSO directly, or the bits that are stored in
-debuginfo files if we find it installed (so smaller). We could strip
that down further by storing just the ELF sections needed to make sense
of the symtab.

- Arnaldo