RELENG_4 -> 5 -> 6: significant performance regression

[Chris]

On 28/04/06, Kris Kennaway <kris at obsecurity.org> wrote:
> On Fri, Apr 28, 2006 at 03:31:17PM +0300, Dmitry Pryanishnikov wrote:
> >
> > Hello!
> >
> > On Thu, 27 Apr 2006, Kris Kennaway wrote:
> >
> >  Thanks for your suggestions, they've made a difference (though not as big
> > as one could hope).
> >
> > >On Thu, Apr 27, 2006 at 05:08:11PM +0300, Dmitry Pryanishnikov wrote:
> > >
> > >>makeoptions CONF_CFLAGS=-fno-builtin
> > >
> > >Non-default option; this may conceivably affect performance.
> >
> >  The reason why I've initially included this option is the following
> > comment (NOTES from RELENG_6):
> >
> > #
> > # CONF_CFLAGS gives some extra compiler flags that are added to ${CFLAGS}
> > # after most other flags.  Here we use it to inhibit use of non-optimal
> > # gcc builtin functions (e.g., memcmp).
> > #
> >
> > I've read this: using "CONF_CFLAGS=-fno-builtin" inhibits use of non-optimal
> > gcc builtin functions, so this option may be useful for getting max.
> > performance. Are this comment and my interpretation still correct now?
>
> I don't know, it needs to be tested in your particular case.
>
> > >>                 %Sys   %Intr   %Idl
> > >>RELENG_4 + rl0      14      14     72
> > >>RELENG_4 + fxp0     14      10     76
> > >>RELENG_5 + rl0      40      30     30
> > >>RELENG_5 + fxp0     35      25     40
> > >>RELENG_6 + rl0      45      40     15
> > >>RELENG_6 + fxp0     45      35     20
>
> >                   %Sys   %Intr   %Idl  "time md5 -t" wall clock time
> > RELENG_5 + rl0      33      23     44   1:41
> > RELENG_5 + fxp0     30      20     50   1:36
> >
> > RELENG_6 + rl0      34      24     42   1:43
> > RELENG_6 + fxp0     30      20     50   1:40
> >
> > So performance now is much better then before removal of
> >
> > makeoptions   CONF_CFLAGS=-fno-builtin
> > options       INVARIANTS
> > options       INVARIANT_SUPPORT
> > options       QUOTA
> >
> > (I'll try to find out which one of these takes which % of overhead when I
> > get free time), but still much worse then under RELENG_4, where this
> > particular (I'd say "quote common") usage pattern takes 24-28% of CPU time,
> > while under RELENG_5 / 6 it takes >= 50% ;(
>
> Thanks.  Silly question: the data transfer rate is the same on both
> 4.x and 6.x, right?  i.e. the data transfer itself takes the same
> time?
>
> The next step is for you to run some profiling tests to see
> where the kernel is spending time, e.g. with hwpmc.
>
> Also, when you are trying to quantify performance differences, you
> need to run many copies of the test (at least 10) under identical
> conditions to account for possible variations.  The ministat tool
> (/usr/src/tools/tools/ministat) is good for performing statistically
> meaningful comparisons of data sets when you have them.
>
> Kris

Does 'makeoptions     DEBUG=-g' add any kind of performance hit or
overhead as I noticed it wasnt default in 5.4 but is in 6.0.

Thanks

Chris