svn commit: r209119 - head/sys/sys

[Roman Divacky]

On Sun, Jun 13, 2010 at 01:59:11PM +0000, mdf at FreeBSD.org wrote:
> On Sun, Jun 13, 2010 at 10:10 AM, Pawel Jakub Dawidek <pjd at freebsd.org> wrote:
> > On Sun, Jun 13, 2010 at 02:39:55AM +0000, Lawrence Stewart wrote:
> >> Author: lstewart
> >> Date: Sun Jun 13 02:39:55 2010
> >> New Revision: 209119
> >> URL: http://svn.freebsd.org/changeset/base/209119
> >>
> >> Log:
> >> ? Add a utility macro to simplify calculating an aggregate sum from a DPCPU
> >> ? counter variable.
> >>
> >> ? Sponsored by: ? ? ? FreeBSD Foundation
> >> ? Reviewed by: ? ? ? ?jhb, rpaulo, rwatson (previous version of patch)
> >> ? MFC after: ?1 week
> >>
> >> Modified:
> >> ? head/sys/sys/pcpu.h
> >>
> >> Modified: head/sys/sys/pcpu.h
> >> ==============================================================================
> >> --- head/sys/sys/pcpu.h ? ? ? Sun Jun 13 01:27:29 2010 ? ? ? ?(r209118)
> >> +++ head/sys/sys/pcpu.h ? ? ? Sun Jun 13 02:39:55 2010 ? ? ? ?(r209119)
> >> @@ -106,6 +106,17 @@ extern uintptr_t dpcpu_off[];
> >> ?#define ? ? ?DPCPU_ID_GET(i, n) ? ? ?(*DPCPU_ID_PTR(i, n))
> >> ?#define ? ? ?DPCPU_ID_SET(i, n, v) ? (*DPCPU_ID_PTR(i, n) = v)
> >>
> >> +/*
> >> + * Utility macros.
> >> + */
> >> +#define DPCPU_SUM(n, var, sum) ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? \
> >> +do { ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? \
> >> + ? ? (sum) = 0; ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ?\
> >> + ? ? u_int i; ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ?\
> >> + ? ? CPU_FOREACH(i) ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ?\
> >> + ? ? ? ? ? ? (sum) += (DPCPU_ID_PTR(i, n))->var; ? ? ? ? ? ? ? ? ? ? \
> >> +} while (0)
> >
> > I'd suggest first swapping variable declaration and '(sum) = 0;'.
> > Also using 'i' as a counter in macro can easly lead to name collision.
> > If you need to do it, I'd suggest '_i' or something.
> > Maybe it would be better to make it an inline function rather than macro?
> 
> (Relevant but almost a thread hijack):
> 
> At Isilon we've run into a lot of problems with variable declarations
> in macros, especially with -Wshadow turned on.  We ended up
> backporting __COUNTER__ from later versions of gcc and then using it
> to make unique variable names.
> 
>  - is the backport (or a fresh implementation) something that could be
> done within the scope of the GPL license?
>  - is it something FreeBSD would be interested in?
>  - is __COUNTER__ supported by clang?

__COUNTER__ is supported by clang