Re: [PATCH 1/25] Remove nested functions: crypt/md5-crypt.c

[Siddhesh Poyarekar <siddhesh at redhat dot com>]

On Tue, May 20, 2014 at 06:23:40PM +0400, Konstantin Serebryany wrote:
> Do you think such a benchmarks is possible at all?
> I've made a simple test (attached) and profiled it with "perf":
>     85.26%    a.out  libcrypt-2.15.so   [.] _ufc_doit_r
>      6.13%    a.out  libcrypt-2.15.so   [.] _ufc_mk_keytab_r
>      2.40%    a.out  libcrypt-2.15.so   [.] _ufc_setup_salt_r
>      1.56%    a.out  libcrypt-2.15.so   [.] __crypt_r
>      1.51%    a.out  libcrypt-2.15.so   [.] _ufc_output_conversion_r
>      1.35%    a.out  libcrypt-2.15.so   [.] crypt
> 
> As you can see, crypt_r itself takes a tiny fraction of time,
> most of it is spent in _ufc_* which are defined in another module.
> Any changes in crypt itself (unless you do something insane) will not
> be observable in profile.

You'll need to choose inputs so that __md5_crypt_r is called -
crypt/crypt-entry.c should help you with that.  if __md5_crypt_r takes
a tiny fraction of time again, then this change should be safe, but I
would prefer that the inputs get fed into the benchtests anyway so
that we can automatically track performance of crypt for those inputs
in future.

Siddhesh

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