Date: Sun, 13 Jun 2010 13:59:11 +0000 From: mdf@FreeBSD.org To: Pawel Jakub Dawidek <pjd@freebsd.org> Cc: svn-src-head@freebsd.org, Lawrence Stewart <lstewart@freebsd.org>, svn-src-all@freebsd.org, src-committers@freebsd.org Subject: Re: svn commit: r209119 - head/sys/sys Message-ID: <AANLkTik2X_x6cNsLWQTNqDHuN69IZgyMnM--0vhp36xk@mail.gmail.com> In-Reply-To: <20100613101025.GD1320@garage.freebsd.pl> References: <201006130239.o5D2du3m086332@svn.freebsd.org> <20100613101025.GD1320@garage.freebsd.pl>
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On Sun, Jun 13, 2010 at 10:10 AM, Pawel Jakub Dawidek <pjd@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? - if not, could it be? -Wshadow found several nasty bugs in our code, and apart from a few spurious warnings it has been handy to have when building our filesystem. Thanks, matthew
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