RELENG_4 -> 5 -> 6: significant performance regression

[Kris Kennaway]

On Sat, May 13, 2006 at 08:59:01AM +0300, Dmitry Pryanishnikov wrote:
> 
> Hello!
> 
> On Fri, 12 May 2006, Kris Kennaway wrote:
> >>>>>>               %Sys   %Intr   %Idl
> >>>>>>RELENG_6 + rl0      45      40     15
> >>>>>>RELENG_6 + fxp0     45      35     20
> >>>
> >>>>                 %Sys   %Intr   %Idl  "time md5 -t" wall clock time
> >>>>RELENG_6 + rl0      34      24     42   1:43
> >>>>RELENG_6 + fxp0     30      20     50   1:40
> >>
> >>is caused by just these:
> >>
> >>options 	INVARIANTS
> >>options 	INVARIANT_SUPPORT
> >
> >So what is the overall status?  I am not clear what your results are.
> 
>  Results for RELENG_6+rl0 are
> 
> %Sys   %Intr   %Idl
> 34      24     42
> 
> without INVARIANTS, and
> 
> %Sys   %Intr   %Idl
> 45      40     15
> 
> with them. Other options like QUOTA and "makeoptions
> CONF_CFLAGS=-fno-builtin" make almost no difference. So, under my test
> conditions, the best % of idle CPU time under RELENG_6 is 42%, while under 
> RELENG_4 we had
> 
> %Sys   %Intr   %Idl
> 14      14     72
> 
> under the same conditions (and with INVARIANTS!) ;(

OK, thanks.  In order to understand the differences you will need to
proceed to detailed profiling traces as I previously mentioned.

With respect to INVARIANTS, you just need to get used to the fact that
running thousands of checks for bugs is incompatible with running at
optimal speed.  The effect is cumulative over time: as more checks are
added (and since they are essentially never removed), checks that are
individually very cheap become collectively quite expensive.  It is
not feasible to only enable the subset of the thousands of checks that
are going to find the most bugs.

Kris
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