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Date: Fri, 13 Mar 2015 17:20:11 +0100
From: Jiri Olsa <jolsa@redhat.com>
To: Arnaldo Carvalho de Melo <acme@redhat.com>
Cc: Jiri Olsa <jolsa@kernel.org>, linux-kernel@vger.kernel.org,
        Corey Ashford <cjashfor@linux.vnet.ibm.com>,
        David Ahern <david.ahern@oracle.com>, Ingo Molnar <mingo@kernel.org>,
        Namhyung Kim <namhyung@kernel.org>, Paul Mackerras <paulus@samba.org>,
        Peter Zijlstra <peterz@infradead.org>
Subject: Re: [PATCH 01/15] perf build: Disable default check for libbabeltrace
Message-ID: <20150313162011.GA21865@krava.brq.redhat.com>
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On Fri, Mar 13, 2015 at 12:36:21PM -0300, Arnaldo Carvalho de Melo wrote:

SNIP

> 
> Auto-detecting system features:
> ...                         dwarf: [ on  ]
> ...                         glibc: [ on  ]
> ...                          gtk2: [ on  ]
> ...                      libaudit: [ on  ]
> ...                        libbfd: [ on  ]
> ...                        libelf: [ on  ]
> ...                       libnuma: [ on  ]
> ...                       libperl: [ on  ]
> ...                     libpython: [ on  ]
> ...                      libslang: [ on  ]
> ...                     libunwind: [ OFF ]
> ...            libdw-dwarf-unwind: [ on  ]
> ...                          zlib: [ on  ]
> ...     DWARF post unwind library: libdw
> 
>   GEN      common-cmds.h
> 
> It continues trying to find babeltrace, does not find it, emits the warning and
> just doesn't show the OFF message :-\
> 
> Can you explain _why_ this is needed?  I.e. is it to speed up feature checking?
> In what way, etc. For casual readers the intent of this patch may be difficult
> to grasp, no?
> 
> What am I missing?

this patch removes babeltrace from:
  - detected features display  -> so user's not curious where to get the latest babeltrace version ;-)
  - test-all optimization      -> so we could use features build speed up, missing babeltrace was stoping this

but we still check for babeltrace (out of the default list code)
in order to enable the ctf convert code if it's in the system

I admit the extra warning about missing babeltrace support
might be confusing, I can remove it.. ;-)

I think we could add new class of features that are enabled
just on demand and not checked by default at all, like:
  'make BABELTRACE=1' or via .config,
but we need to add support for that first

jirka