netdev - RE: [PATCH 4/6] arm64/io: Provide a WC friendly __iowriteXX

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Message-ID: <3227d5224a9745e388738d016fdae87a@AcuMS.aculab.com>
Date: Fri, 23 Feb 2024 11:05:29 +0000
From: David Laight <David.Laight@...LAB.COM>
To: 'Niklas Schnelle' <schnelle@...ux.ibm.com>, 'Jason Gunthorpe'
	<jgg@...dia.com>
CC: Alexander Gordeev <agordeev@...ux.ibm.com>, Andrew Morton
	<akpm@...ux-foundation.org>, Christian Borntraeger
	<borntraeger@...ux.ibm.com>, Borislav Petkov <bp@...en8.de>, Dave Hansen
	<dave.hansen@...ux.intel.com>, "David S. Miller" <davem@...emloft.net>, "Eric
 Dumazet" <edumazet@...gle.com>, Gerald Schaefer
	<gerald.schaefer@...ux.ibm.com>, Vasily Gorbik <gor@...ux.ibm.com>, "Heiko
 Carstens" <hca@...ux.ibm.com>, "H. Peter Anvin" <hpa@...or.com>, Justin Stitt
	<justinstitt@...gle.com>, Jakub Kicinski <kuba@...nel.org>, Leon Romanovsky
	<leon@...nel.org>, "linux-rdma@...r.kernel.org" <linux-rdma@...r.kernel.org>,
	"linux-s390@...r.kernel.org" <linux-s390@...r.kernel.org>,
	"llvm@...ts.linux.dev" <llvm@...ts.linux.dev>, Ingo Molnar
	<mingo@...hat.com>, Bill Wendling <morbo@...gle.com>, Nathan Chancellor
	<nathan@...nel.org>, Nick Desaulniers <ndesaulniers@...gle.com>,
	"netdev@...r.kernel.org" <netdev@...r.kernel.org>, Paolo Abeni
	<pabeni@...hat.com>, Salil Mehta <salil.mehta@...wei.com>, Jijie Shao
	<shaojijie@...wei.com>, Sven Schnelle <svens@...ux.ibm.com>, Thomas Gleixner
	<tglx@...utronix.de>, "x86@...nel.org" <x86@...nel.org>, Yisen Zhuang
	<yisen.zhuang@...wei.com>, Arnd Bergmann <arnd@...db.de>, Catalin Marinas
	<catalin.marinas@....com>, Leon Romanovsky <leonro@...lanox.com>,
	"linux-arch@...r.kernel.org" <linux-arch@...r.kernel.org>,
	"linux-arm-kernel@...ts.infradead.org"
	<linux-arm-kernel@...ts.infradead.org>, Mark Rutland <mark.rutland@....com>,
	Michael Guralnik <michaelgur@...lanox.com>, "patches@...ts.linux.dev"
	<patches@...ts.linux.dev>, Will Deacon <will@...nel.org>
Subject: RE: [PATCH 4/6] arm64/io: Provide a WC friendly __iowriteXX_copy()

...
> > > > > +		if ((_count % 8) >= 4) {
> > > >
> > > > If (_count & 4) {
> > >
> > > That would be obfuscating, IMHO. The compiler doesn't need such things
> > > to generate optimal code.
> >
> > Try it: https://godbolt.org/z/EvvGrTxv3
> > And it isn't that obfuscated - no more so than your version.
> 
> The godbolt link does "n % 8 > 4" instead of "... >= 4" as in Jason's
> original code. With ">=" the compiled code matches that for "n & 4".

Bugger :-)

	David

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