Date: Mon, 14 Jun 2010 23:26:14 +1000 (EST) From: Bruce Evans <brde@optusnet.com.au> 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: <20100614230205.A37830@delplex.bde.org> In-Reply-To: <4C14E012.7080902@freebsd.org> References: <201006130239.o5D2du3m086332@svn.freebsd.org> <20100613101025.GD1320@garage.freebsd.pl> <4C14E012.7080902@freebsd.org>
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On Sun, 13 Jun 2010, 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:
>>> 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;'.
Of course.
Also fix the lexical style bugs:
- space instead of tab after #define
- "do {" at the beginning of a line (see queue.h for normal style)
- missing blank line after declarations
- missing braces around loop body (*).
>
> Can do (will wait until consensus on other issues is reached first before
> tweaking though).
>
>> Also using 'i' as a counter in macro can easly lead to name collision.
>
> I had a similar concern but after chatting with John on IRC felt it wasn't
> such a big deal in this case.
>
>> If you need to do it, I'd suggest '_i' or something.
>
> Could do... is it worth it?
>
>> Maybe it would be better to make it an inline function rather than macro?
>
> Inlining it could be annoying with respect to the types used in the function
> prototype, no? I suspect it would be more useful keeping it as a macro if
> possible.
Inlining it is impossible for the same reason that parenthesizing all the
macro args would be impossible -- `var' is a name and parenthesizing its
use would give the syntax error foo->(var). Not sure about (n). It's
a little surprising that parenthesizing works for lvalues like (sum)
(it works because lvalues include certain expressions including
parenthesized ones, but I wonder if it ever makes a difference).
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().
(*) style(9) recommends leaving out these unnecessary braces. However,
mistakes like CPU_FOREACH() look less like syntax errors with the braces
than without them; the braces at least confuse indent(1) into not making
a mess. indent(1) already knows that it doesn't understand macros so it
doesn't reformat them, so this doesn't quite apply here.
Bruce
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