Re: [lmi] perf

[Greg Chicares]

On 2020-09-27 17:57, Vadim Zeitlin wrote:
> On Sat, 26 Sep 2020 23:14:21 +0000 Greg Chicares <gchicares@sbcglobal.net> 
> wrote:
> 
> GC> My normal user doesn't have CAP_SYS_ADMIN. Apparently if you have
> GC> that, you're almost root anyway, so I'm reluctant to give myself
> GC> that privilege--at least when I become root, I'm aware that I need
> GC> to be especially careful. Do you use root, or grant your normal
> GC> user CAP_SYS_ADMIN, or run 'perf' in some other way?
> 
>  I just do what, I think, it told me to do, once I've tried using it
> unsuccessfully, i.e. set kernel.perf_event_paranoid kernel parameter to 0
> or -1 depending on my current actual level of paranoia. This can, of
> course, be done temporarily, if you run perf only episodically.
> 
>  FWIW I definitely don't run perf as root -- not because I don't trust perf
> itself, but because I don't trust my own programs, that would also run as
> root then.

Oh. I didn't think of that. I guess that 'paranoid' thing is the
least dangerous option.

> GC> I couldn't easily install 'linux-perf' in the out-of-date chroot
> GC> that I'm still using for production, due to conflicts in its
> GC> required components, and I don't want to update it because I'm
> GC> using it for production (and the MinGW-w64-gcc version would
> GC> change to something we're not using in production yet). I had
> GC> the seemingly brilliant idea of running 'perf' in my host
> GC> (after installing it successfully there) to profile a binary
> GC> in a chroot:
> GC> 
> GC> lmipath=/srv/chroot/bullseye0/opt/lmi/gcc_x86_64-pc-linux-gnu/build/ship; 
> \
> GC>  LD_LIBRARY_PATH=$lmipath; \
> GC>  $lmipath/lmi_cli_shared --accept --data_path=/opt/lmi/data --selftest
> GC> 
> GC> However:

[...and hilarity ensues...]

>  I don't really know what's going on here, but trying to run a binary from
> chroot outside of chroot just seems weird. OTOH I still think you ought to
> be able to run "perf record schroot -c bullseye0 /path/to/lmi_cli_shared"
> or something like this, shouldn't you?

Thanks, I didn't think of that.

> GC> Instead of trying to deal with these problems, I'll just create a new
> GC> chroot (including 'perf').
> 
>  Note that perf version must correspond to the kernel version, so you can
> only use it inside chroot if it uses the same kernel packages as the main
> system, which is usually _not_ the case -- unless you install the same
> system that you're already using inside a chroot, which is definitely
> possible, but doesn't seem really necessary.

Fortunately I didn't see your reply earlier, as it would have
robbed me of the joy of discovery:
  10035ba0 Revert "Install 'perf'"
  34fb78df Install 'perf'