svn commit: r209119 - head/sys/sys

[John Baldwin]

On Monday 14 June 2010 9:50:10 am mdf at freebsd.org wrote:
> > BTW, one reason I liked BSD code more than gnu code is that it didn't
> > use so many macros.  Macros should only exist when they are not just
> > syntactic sugar, like DPCPU_SUM() and unlike CPU_FOREACH().
> 
> As a style question, I do understand (generally) why too many macros
> make the code confusing.  However, the *FOREACH macros all fit the
> same pattern and having a macro to iterate protects one against
> changes in the implementation -- there's a single location to change
> if e.g. we want to make CPU_FOREACH use a bitwise operator to
> determine the next non-zero bit, rather than testing each
> individually.

In the case of CPU_FOREACH() there is a very good chance that the 
implementation details will change when we switch from cpumask_t to cpuset_t, 
which is part of the reason I added it.  I am less of a fan of macros that 
just wrap TAILQ_FOREACH() (note that there isn't a PCPU_FOREACH() since you 
can already do this via SLIST_FOREACH() now for example) such as 
FOREACH_PROC_IN_SYSTEM().  CPU_FOREACH() has additional logic in that it hides 
the CPU_ABSENT() stuff, so to me it doesn't quite fall in that class.  (Some 
code was using pcpu_find() instead of CPU_ABSENT() to determine absent CPUs as 
well FWIW.)

-- 
John Baldwin