linux-kernel - Re: [RFC 6/6] perf build: Introduce FEATURES

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Message-ID: <20160113091913.GA4487@krava.brq.redhat.com>
Date:	Wed, 13 Jan 2016 10:19:13 +0100
From:	Jiri Olsa <jolsa@...hat.com>
To:	"Wangnan (F)" <wangnan0@...wei.com>
Cc:	Jiri Olsa <jolsa@...nel.org>,
	Arnaldo Carvalho de Melo <acme@...nel.org>,
	lkml <linux-kernel@...r.kernel.org>,
	David Ahern <dsahern@...il.com>,
	Ingo Molnar <mingo@...nel.org>,
	Namhyung Kim <namhyung@...nel.org>,
	Peter Zijlstra <a.p.zijlstra@...llo.nl>
Subject: Re: [RFC 6/6] perf build: Introduce FEATURES_DUMP make variable

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?

thanks,
jirka