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Date: Wed, 13 Jan 2016 17:46:13 +0800
From: "Wangnan (F)" <wangnan0@huawei.com>
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To: Jiri Olsa <jolsa@redhat.com>
CC: Jiri Olsa <jolsa@kernel.org>, Arnaldo Carvalho de Melo <acme@kernel.org>,
        lkml <linux-kernel@vger.kernel.org>, David Ahern <dsahern@gmail.com>,
        "Ingo Molnar" <mingo@kernel.org>, Namhyung Kim <namhyung@kernel.org>,
        Peter Zijlstra <a.p.zijlstra@chello.nl>
Subject: Re: [RFC 6/6] perf build: Introduce FEATURES_DUMP make variable
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On 2016/1/13 17:19, Jiri Olsa wrote:
> On Tue, Jan 12, 2016 at 05:28:28PM +0800, Wangnan (F) wrote:
>
> SNIP
>
>> For example:
>>
>> $ make feature-dump LDFLAGS="-static"
>>    BUILD:   Doing 'make -j24' parallel build
>>
>> Auto-detecting system features:
>> <SNIP>
>> ...                          zlib: [ on  ]
>> ...                          lzma: [ OFF ]     <--- looks good. I don't have
>> static lzma library
>> ...                     get_cpuid: [ on  ]
>> ...                           bpf: [ on  ]
>>
>>
>> $ make feature-dump
>>    BUILD:   Doing 'make -j24' parallel build
>>
>> Auto-detecting system features:
>> <SNIP>
>> ...                          zlib: [ on  ]
>> ...                          lzma: [ on  ]   <--- also good
>> ...                     get_cpuid: [ on  ]
>> ...                           bpf: [ on  ]
>>
>>
>> $ make feature-dump LDFLAGS="-static"
>>    BUILD:   Doing 'make -j24' parallel build
>>
>> Auto-detecting system features:
>> <SNIP>
>> ...                          zlib: [ on  ]
>> ...                          lzma: [ on  ]     <--- Bad...
>> ...                     get_cpuid: [ on  ]
>> ...                           bpf: [ on  ]
>>
>> Thank you.
> right, it's because feature is not under build framework and
> compilation does not care about flags change..
>
> I'll try to check on that.. does this patch help to improve
> the current speed or do you need to solve this to get substantial
> speedup?

I'm working on it. I have already done it, but still have some
problem. On some machine 'make_static' test target lost
'-liberty -lz' in its linker options. Seems something wrong in
this part:

ifeq ($(feature-libbfd), 1)
   EXTLIBS += -lbfd

   # call all detections now so we get correct
   # status in VF output
   $(call feature_check,liberty)
   $(call feature_check,liberty-z)
   $(call feature_check,cplus-demangle)

   ifeq ($(feature-liberty), 1)
     EXTLIBS += -liberty
   else
     ifeq ($(feature-liberty-z), 1)
       EXTLIBS += -liberty -lz
     endif
   endif
endif

On a 24 core machine the build-test takes about 16 mins. Faster than before:

real    16m7.642s
user    171m47.488s
sys    19m10.692s