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Date: Tue, 1 Oct 2013 14:04:55 +0200
From: Ingo Molnar <mingo@kernel.org>
To: Arnaldo Carvalho de Melo <acme@ghostprotocols.net>
Cc: Linus Torvalds <torvalds@linux-foundation.org>,
        David Ahern <dsahern@gmail.com>,
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        Andrew Morton <akpm@linux-foundation.org>,
        Jiri Olsa <jolsa@redhat.com>, Namhyung Kim <namhyung@gmail.com>
Subject: Re: [PATCH] perf autodep: Remove strlcpy feature check, add __weak
 strlcpy implementation
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* Ingo Molnar <mingo@kernel.org> wrote:

> Overhead is down from 0.600 secs to 0.540 secs. The only remaining thing 
> is the libperl bug, I'll have a look at that next.

So, libperl detection works fine here, once I've installed the prereq 
package on Fedora, "perl-ExtUtils-Embed":

  comet:~/tip/tools/perf> make Makefile

Auto-detecting system features:

...            stackprotector-all: [ on  ]
...         volatile-register-var: [ on  ]
...                fortify-source: [ on  ]
...                        libelf: [ on  ]
...                   libelf-mmap: [ on  ]
...                         glibc: [ on  ]
...                         dwarf: [ on  ]
...             libelf-getphdrnum: [ on  ]
...                     libunwind: [ on  ]
...                      libaudit: [ on  ]
...                      libslang: [ on  ]
...                          gtk2: [ on  ]
...                  gtk2-infobar: [ on  ]
...                       libperl: [ on  ]
...                     libpython: [ on  ]
...             libpython-version: [ on  ]
...                        libbfd: [ on  ]
...                       on-exit: [ on  ]
...                     backtrace: [ on  ]
...                       libnuma: [ on  ]

Time is down to 0.480 sec because there are no build failures now, only 
Make re-checking the dependencies of already built binaries.

And the actual feature check is roughly 0.330 msecs of that:

 comet:~/tip/tools/perf/config/feature-checks> time ( make -j >/dev/null; \
 for N in stackprotector-all volatile-register-var fortify-source libelf \
 libelf-mmap glibc dwarf libelf-getphdrnum libunwind libaudit libslang gtk2 \
 gtk2-infobar libperl libpython libpython-version libbfd on-exit backtrace \
 libnuma; do make test-$N >/dev/null; done )

 real    0m0.330s
 user    0m0.290s
 sys     0m0.031s

With 0.150 msecs spent elsewhere.

So there's more speedups possible I think, for example we could construct 
an 'optimistic' testcase that is generated live and includes a 
concatenation of all the testcases.

If the build of that file succeeds then we have a really efficient 
fast-path both in the first-build and in the repeat-build case.

If that build fails then we do the more finegrained feature check.

Thoughts?

Thanks,

	Ingo