Re: [PATCH] perf util: Display warning when perf report/annotate is missing some libs

["Jin, Yao" <yao.jin@linux.intel.com>]

On 3/22/2018 2:52 AM, Arnaldo Carvalho de Melo wrote:
> Em Wed, Mar 21, 2018 at 05:04:46PM +0100, Jiri Olsa escreveu:
>> On Wed, Mar 21, 2018 at 12:43:15PM -0300, Arnaldo Carvalho de Melo wrote:
>>> Em Wed, Mar 21, 2018 at 12:40:35PM -0300, Arnaldo Carvalho de Melo escreveu:
>>>> Em Wed, Mar 21, 2018 at 04:38:07PM +0100, Jiri Olsa escreveu:
>>>>> On Wed, Mar 21, 2018 at 10:11:10AM +0800, Jin, Yao wrote:
>>>>>> Hi Jiri,
>>>>>>
>>>>>> I'm still thinking it's worth displaying the warning when perf missing some
>>>>>> libraries.
>>>>>>
>>>>>> Somebody just told me that perf didn't work well. While after some
>>>>>> investigations, I found it's just missing some libraries when building the
>>>>>> perf.
>>>>>>
>>>>>> But I have spent some time on getting the root cause. If with this patch, it
>>>>>> should be very easily to know that.
> 
>>>>> true.. Arnaldo, any feedback on this one?
> 
>>>> Lemme re-read the thread...
> 
>>> Well, how about we make it harder to build without key libraries? I.e.
>>> if we detect that what we consider a core set of libraries isn't found
>>> in the system, then we stop the build, warn about it and ask the user to
>>> confirm that the build should proceed by passing some explicit
>>> -DI_KNOW_WHAT_I_AM_DOING___PROCEED=doit
> 
>> hum, not sure we want to complicate the build even more than it
>> is now :-\ and IMO it still won't help much in Jin's problem,
>> if user forces the build anyway
> 
> Well, if a user _forces_ a build, not taking into consideration a
> warning that _is_ emitted and _stops_ the build, about the functionality
> it will lose by doing forcing the build, then comes back and complains
> that that functionality is not present, then it becomes difficult to
> help this user...  :-)
> 
> On the other hand, if the user forgets to install an important library,
> the warning is emitted but the build proceeds, no explicit action was
> performed, just a warning wasn't noticed, and the user complains, then
> I'd say: "hey, are you sure library foo devel files were present when
> you build it?", i.e. the support back and forth Jin is trying to avoid.
> 
> And for users that _saw_ the warning, _knew_ they _didn't_ want that
> functionality, to be reminded while running, say 'perf report' that
> something they _decided not to have_ isn't present, then that could be
> annoying, no?
> 
> Lemme try another idea: what if we do something like gcc does and print
> the features present when showing the version?
> 
> I.e.:
> 
> [acme@jouet perf]$ gcc -v
> Using built-in specs.
> COLLECT_GCC=/usr/bin/gcc
> COLLECT_LTO_WRAPPER=/usr/libexec/gcc/x86_64-redhat-linux/7/lto-wrapper
> OFFLOAD_TARGET_NAMES=nvptx-none
> OFFLOAD_TARGET_DEFAULT=1
> Target: x86_64-redhat-linux
> Configured with: ../configure --enable-bootstrap --enable-languages=c,c++,objc,obj-c++,fortran,ada,go,lto --prefix=/usr --mandir=/usr/share/man --infodir=/usr/share/info --with-bugurl=http://bugzilla.redhat.com/bugzilla --enable-shared --enable-threads=posix --enable-checking=release --enable-multilib --with-system-zlib --enable-__cxa_atexit --disable-libunwind-exceptions --enable-gnu-unique-object --enable-linker-build-id --with-gcc-major-version-only --with-linker-hash-style=gnu --enable-plugin --enable-initfini-array --with-isl --enable-libmpx --enable-offload-targets=nvptx-none --without-cuda-driver --enable-gnu-indirect-function --with-tune=generic --with-arch_32=i686 --build=x86_64-redhat-linux
> Thread model: posix
> gcc version 7.3.1 20180303 (Red Hat 7.3.1-5) (GCC)
> [acme@jouet perf]$
> 
> - Arnaldo
> 

Is this too complicated for perf newbie to understand?

For my problem, the mistake only occurs on perf newbie. I just think, 
it'd better return a direct and clear message to them. Maybe they don't 
know or don't use -v or -vv to do more investigation by themselves.

Thanks
Jin Yao