linux-kernel - Re: [RFC PATCH 0/9] Remove useless on_each

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Date:	Tue, 3 Jan 2012 18:08:33 +0200
From:	Gilad Ben-Yossef <gilad@...yossef.com>
To:	Michal Nazarewicz <mina86@...a86.com>
Cc:	linux-kernel@...r.kernel.org, David Airlie <airlied@...ux.ie>,
	dri-devel@...ts.freedesktop.org,
	Benjamin Herrenschmidt <benh@...nel.crashing.org>,
	Paul Mackerras <paulus@...ba.org>,
	Grant Likely <grant.likely@...retlab.ca>,
	Rob Herring <rob.herring@...xeda.com>,
	linuxppc-dev@...ts.ozlabs.org, devicetree-discuss@...ts.ozlabs.org,
	Richard Henderson <rth@...ddle.net>,
	Ivan Kokshaysky <ink@...assic.park.msu.ru>,
	Matt Turner <mattst88@...il.com>, linux-alpha@...r.kernel.org,
	Thomas Gleixner <tglx@...utronix.de>,
	Ingo Molnar <mingo@...hat.com>,
	"H. Peter Anvin" <hpa@...or.com>, x86@...nel.org,
	Tony Luck <tony.luck@...el.com>,
	Fenghua Yu <fenghua.yu@...el.com>, linux-ia64@...r.kernel.org,
	Will Deacon <will.deacon@....com>,
	Peter Zijlstra <a.p.zijlstra@...llo.nl>,
	Arnaldo Carvalho de Melo <acme@...stprotocols.net>,
	Russell King <linux@....linux.org.uk>,
	linux-arm-kernel@...ts.infradead.org
Subject: Re: [RFC PATCH 0/9] Remove useless on_each_cpu return value

2012/1/3 Michal Nazarewicz <mina86@...a86.com>:
> On Tue, 03 Jan 2012 15:19:04 +0100, Gilad Ben-Yossef <gilad@...yossef.com>
> wrote:
>>
>> on_each_cpu() returns as its own return value the return value of
>> smp_call_function(). smp_call_function() in turn returns a hard
>> coded value of zero.
>>
>> Some callers to on_each_cpu() waste cycles and bloat code space
>> by checking the return value to on_each_cpu(), probably for
>> historical reasons.
>>
>> This patch set refactors callers to not test on_each_cpu()
>> (fixed) return value and then refactors on_each_cpu to
>> return void to avoid confusing future users.
>>
>> In other words, this patch aims to delete 18 source code lines
>> while not changing any functionality :-)
>>
>> I tested as best as I could the x86 changes and compiled some
>> of the others, but I don't have access to all the needed hardware
>> for testing. Reviewers and testers welcome!
>
>
> Other then the lack of Signed-off-by in the patches, looks good to me,

Blimey! I'll resend with a proper Signed-off-by after more people have
a chance to
comment. And thanks for the review.

> even though personally I'd choose a bottom-up approach, ie. make
> smp_call_function() return void and from that conclude that
> on_each_cpu() can return void.  With those patches, we have a situation,
> where smp_call_function() has a return value which is then lost for no
> immediately apparent reason lost in on_each_cpu().

There are so many call site of smp_call_function() that do not check the
return value right now that I think we can tolerate it for just a
little bit longer
until that get fixed as well... :-)

Thanks,
Gilad


-- 
Gilad Ben-Yossef
Chief Coffee Drinker
gilad@...yossef.com
Israel Cell: +972-52-8260388
US Cell: +1-973-8260388
http://benyossef.com

"Unfortunately, cache misses are an equal opportunity pain provider."
-- Mike Galbraith, LKML
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