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

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Date:	Tue, 03 Jan 2012 15:25:49 +0100
From:	"Michal Nazarewicz" <mina86@...a86.com>
To:	linux-kernel@...r.kernel.org,
	"Gilad Ben-Yossef" <gilad@...yossef.com>
Cc:	"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

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,
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().

-- 
Best regards,                                         _     _
.o. | Liege of Serenely Enlightened Majesty of      o' \,=./ `o
..o | Computer Science,  Michał “mina86” Nazarewicz    (o o)
ooo +----<email/xmpp: mpn@...gle.com>--------------ooO--(_)--Ooo--
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