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

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Date: Thu, 29 Feb 2024 09:29:59 -0400
From: Jason Gunthorpe <jgg@...dia.com>
To: Catalin Marinas <catalin.marinas@....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-s390@...r.kernel.org,
	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,
	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,
	Yisen Zhuang <yisen.zhuang@...wei.com>,
	Arnd Bergmann <arnd@...db.de>,
	Leon Romanovsky <leonro@...lanox.com>, linux-arch@...r.kernel.org,
	linux-arm-kernel@...ts.infradead.org,
	Mark Rutland <mark.rutland@....com>,
	Michael Guralnik <michaelgur@...lanox.com>, patches@...ts.linux.dev,
	Niklas Schnelle <schnelle@...ux.ibm.com>,
	Will Deacon <will@...nel.org>
Subject: Re: [PATCH 4/6] arm64/io: Provide a WC friendly __iowriteXX_copy()

On Thu, Feb 29, 2024 at 10:33:04AM +0000, Catalin Marinas wrote:
> On Tue, Feb 20, 2024 at 09:17:08PM -0400, Jason Gunthorpe wrote:
> > +						 const u32 *from, size_t count)
> > +{
> > +	switch (count) {
> > +	case 8:
> > +		asm volatile("str %w0, [%8, #4 * 0]\n"
> > +			     "str %w1, [%8, #4 * 1]\n"
> > +			     "str %w2, [%8, #4 * 2]\n"
> > +			     "str %w3, [%8, #4 * 3]\n"
> > +			     "str %w4, [%8, #4 * 4]\n"
> > +			     "str %w5, [%8, #4 * 5]\n"
> > +			     "str %w6, [%8, #4 * 6]\n"
> > +			     "str %w7, [%8, #4 * 7]\n"
> > +			     :
> > +			     : "rZ"(from[0]), "rZ"(from[1]), "rZ"(from[2]),
> > +			       "rZ"(from[3]), "rZ"(from[4]), "rZ"(from[5]),
> > +			       "rZ"(from[6]), "rZ"(from[7]), "r"(to));
> > +		break;
> 
> BTW, talking of maintenance, would a series of __raw_writel() with
> Mark's recent patch for offset addressing generate similar code? I.e.:

No

gcc intersperses reads/writes (which we were advised not to do) and
clang doesn't support the "o" directive so it produces poor
codegen.

Jason