Date: Mon, 14 Jun 2010 13:43:49 +0300 From: Kostik Belousov <kostikbel@gmail.com> To: Lawrence Stewart <lstewart@freebsd.org> Cc: svn-src-head@freebsd.org, svn-src-all@freebsd.org, src-committers@freebsd.org, Pawel Jakub Dawidek <pjd@freebsd.org> Subject: Re: svn commit: r209119 - head/sys/sys Message-ID: <20100614104349.GF13238@deviant.kiev.zoral.com.ua> In-Reply-To: <4C1605A7.2000202@freebsd.org> References: <201006130239.o5D2du3m086332@svn.freebsd.org> <20100613101025.GD1320@garage.freebsd.pl> <4C158B71.205@freebsd.org> <20100614085205.GD13238@deviant.kiev.zoral.com.ua> <4C1605A7.2000202@freebsd.org>
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On Mon, Jun 14, 2010 at 08:34:15PM +1000, Lawrence Stewart wrote:
> On 06/14/10 18:52, Kostik Belousov wrote:
> >On Mon, Jun 14, 2010 at 11:52:49AM +1000, Lawrence Stewart wrote:
> >>On 06/13/10 20:10, Pawel Jakub Dawidek wrote:
> >>>On Sun, Jun 13, 2010 at 02:39:55AM +0000, Lawrence Stewart wrote:
> >>[snip]
> >>>>
> >>>>Modified: head/sys/sys/pcpu.h
> >>>>=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=
=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=
=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=
=3D=3D=3D=3D=3D
> >>>>--- 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) =3D v)
> >>>>
> >>>>+/*
> >>>>+ * Utility macros.
> >>>>+ */
> >>>>+#define DPCPU_SUM(n, var, sum) \
> >>>>+do { \
> >>>>+ (sum) =3D 0; \
> >>>>+ u_int i; \
> >>>>+ CPU_FOREACH(i) \
> >>>>+ (sum) +=3D (DPCPU_ID_PTR(i, n))->var; \
> >>>>+} while (0)
> >>>
> >>>I'd suggest first swapping variable declaration and '(sum) =3D 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.
> >>
> >>Given that the DPCPU variable name space is flat and variable names have
> >>to be unique, perhaps something like the following would address the
> >>concerns raised?
> >>
> >>#define DPCPU_SUM(n, var, sum) \
> >>do { \
> >> u_int _##n##_i; =
\
> >> (sum) =3D 0; =
\
> >> CPU_FOREACH(_##n##_i) =
\
> >> (sum) +=3D (DPCPU_ID_PTR(_##n##_i, n))->var; =
\
> >>} while (0)
> >
> >You do not have to jump through this. Mostly by convention, in our kernel
> >sources, names with "_" prefix are reserved for the infrastructure (cann=
ot
> >say implementation). I think it is quite safe to use _i for the iteration
> >variable.
> >
> >As an example of this, look at sys/sys/mount.h, implementation of
> >VFS_NEEDGIANT, VFS_LOCK_GIANT etc macros. They do use gcc ({}) extension
> >to provide function-like macros, but this is irrelevant. Or, look at
> >the VFS_ASSERT_GIANT that is exactly like what you need.
>=20
> Ok cool, thanks for the info and pointers (I didn't know about the ({})=
=20
> extension or that "_" prefix was definitely reserved). I'm happy to use=
=20
> _i. Does the following diff against head look suitable to commit?
>=20
> --- a/sys/sys/pcpu.h Sun Jun 13 02:39:55 2010 +0000
> +++ b/sys/sys/pcpu.h Mon Jun 14 20:12:27 2010 +1000
> @@ -111,10 +111,10 @@
> */
> #define DPCPU_SUM(n, var, sum) \
> do { \
> + u_int _i; \
> (sum) =3D 0; \
> - u_int i; \
> - CPU_FOREACH(i) \
> - (sum) +=3D (DPCPU_ID_PTR(i, n))->var; \
> + CPU_FOREACH(_i) \
> + (sum) +=3D (DPCPU_ID_PTR(_i, n))->var; \
> } while (0)
You might want to introduce local accumulator to prevent several evaluations
of sum, to avoid possible side-effects. Then, after, the loop, do single
asignment to the the sum.
Or, you could ditch the sum at all, indeed using ({}) and returning the
result. __typeof is your friend to select proper type of accumulator.
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