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Re: [PATCH 1/25] Remove nested functions: crypt/md5-crypt.c
- From: "Joseph S. Myers" <joseph at codesourcery dot com>
- To: Siddhesh Poyarekar <siddhesh at redhat dot com>
- Cc: Konstantin Serebryany <konstantin dot s dot serebryany at gmail dot com>, GNU C Library <libc-alpha at sourceware dot org>
- Date: Tue, 20 May 2014 14:54:41 +0000
- Subject: Re: [PATCH 1/25] Remove nested functions: crypt/md5-crypt.c
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- References: <CAGQ9bdzqT1EyXYMwACrHpPU=vPjM_b72LJRjb7BW_OzJRXG3bw at mail dot gmail dot com> <20140520131314 dot GB14500 at spoyarek dot pnq dot redhat dot com> <CAGQ9bdw=-pzbi00gn5t_W8pXBjU0edFvLGMNUc+o=g9og=f9+Q at mail dot gmail dot com> <20140520144605 dot GE14500 at spoyarek dot pnq dot redhat dot com>
On Tue, 20 May 2014, Siddhesh Poyarekar wrote:
> 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.
Another thing that can be done is to look at the code generated for the
relevant file before and after the patch - I'd expect very little change.
Joseph S. Myers