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Miller" , Saeed Mahameed , Leon Romanovsky , Mark Bloch , Sabrina Dubroca , netdev@vger.kernel.org, linux-rdma@vger.kernel.org, linux-kernel@vger.kernel.org, Gal Pressman , Leon Romanovsky , Michael Guralnik , Moshe Shemesh , Will Deacon , Alexander Gordeev , Andrew Morton , Christian Borntraeger , Borislav Petkov , Dave Hansen , Gerald Schaefer , Vasily Gorbik , Heiko Carstens , "H. Peter Anvin" , Justin Stitt , linux-s390@vger.kernel.org, llvm@lists.linux.dev, Ingo Molnar , Bill Wendling , Nick Desaulniers , Salil Mehta , Sven Schnelle , Thomas Gleixner , x86@kernel.org, Yisen Zhuang , Arnd Bergmann , Leon Romanovsky , linux-arch@vger.kernel.org, linux-arm-kernel@lists.infradead.org, Mark Rutland , Michael Guralnik , patches@lists.linux.dev, Niklas Schnelle , Jijie Shao References: <1757925308-614943-1-git-send-email-tariqt@nvidia.com> <20250915221859.GB925462@ax162> <20250915222758.GC925462@ax162> <20250915224810.GM1024672@nvidia.com> <20250915231506.GA973819@ax162> Content-Language: en-US From: Patrisious Haddad In-Reply-To: <20250915231506.GA973819@ax162> Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 8bit X-ClientProxiedBy: TLZP290CA0002.ISRP290.PROD.OUTLOOK.COM (2603:1096:950:9::8) To CH3PR12MB8583.namprd12.prod.outlook.com (2603:10b6:610:15f::12) Precedence: bulk X-Mailing-List: netdev@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 X-MS-PublicTrafficType: Email X-MS-TrafficTypeDiagnostic: CH3PR12MB8583:EE_|DS4PR12MB9769:EE_ X-MS-Office365-Filtering-Correlation-Id: e2fe3cdc-510c-4922-eab3-08ddf4fc85c5 X-MS-Exchange-SenderADCheck: 1 X-MS-Exchange-AntiSpam-Relay: 0 X-Microsoft-Antispam: BCL:0;ARA:13230040|366016|1800799024|7416014|376014; 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I think this needs to be CFLAGS instead of FLAGS >>>> but I did not test to verify. >>> Also, Documentation/core-api/floating-point.rst states that code should >>> also use CFLAGS_REMOVE_ for CC_FLAGS_NO_FPU as well as adding >>> CC_FLAGS_FPU. >>> >>> CFLAGS_REMOVE_lib/wc_neon_iowrite64_copy.o += $(CC_FLAGS_NO_FPU) >> I wondered if you needed the seperate compilation unit at all since it >> it all done with inline assembly.. Since the makefile seems to have a >> typo, it suggests you don't need the compilation unit and it could >> just be a little inline protected by CONFIG_KERNEL_MODE_NEON. There is difference between what actually compiles and the effect of these flags on actual performance/assembly translation. To avoid finding that the hard way I prefer to stick to their documentation which does as Natan described below, a separate compilation unit between begin and end and the correct flags - and eventually that was what I tested , I missed to re-test this post finishing my code review - thinking my changes were only cosmetic ... > Hmmm, clang rejects the current patch > > drivers/net/ethernet/mellanox/mlx5/core/lib/wc_neon_iowrite64_copy.c:9:3: error: instruction requires: neon > 9 | ("ld1 {v0.16b, v1.16b, v2.16b, v3.16b}, [%0]\n\t" > | ^ > :1:2: note: instantiated into assembly here > 1 | ld1 {v0.16b, v1.16b, v2.16b, v3.16b}, [x19] > | ^ > drivers/net/ethernet/mellanox/mlx5/core/lib/wc_neon_iowrite64_copy.c:9:48: error: instruction requires: neon > 9 | ("ld1 {v0.16b, v1.16b, v2.16b, v3.16b}, [%0]\n\t" > | ^ > :2:2: note: instantiated into assembly here > 2 | st1 {v0.16b, v1.16b, v2.16b, v3.16b}, [x20] > | ^ > > while GCC accepts it... It looks like GCC's -mgeneral-regs-only only > impacts the compiler using floating-point and SIMD registers after [1] > in GCC 6.x, whereas clang's restriction is on both the compiler and > assembler. Perhaps clang should be adjusted to match but its behavior > seems more desirable for the kernel to ensure floating-point code is > properly separated and called between kernel_fpu_{begin,end}(). This > error is resolved with the following diff. > > [1]: https://gcc.gnu.org/cgit/gcc/commit/?id=7d9425d46b58e69667300331aa55ebddddcceaeb > > Cheers, > Nathan > > diff --git a/drivers/net/ethernet/mellanox/mlx5/core/Makefile b/drivers/net/ethernet/mellanox/mlx5/core/Makefile > index 06d0eb190816..a85fc21419d8 100644 > --- a/drivers/net/ethernet/mellanox/mlx5/core/Makefile > +++ b/drivers/net/ethernet/mellanox/mlx5/core/Makefile > @@ -181,4 +181,5 @@ mlx5_dpll-y := dpll.o > # NEON WC specific for mlx5 > # > mlx5_core-$(CONFIG_KERNEL_MODE_NEON) += lib/wc_neon_iowrite64_copy.o > -FLAGS_lib/wc_neon_iowrite64_copy.o += $(CC_FLAGS_FPU) > +CFLAGS_lib/wc_neon_iowrite64_copy.o += $(CC_FLAGS_FPU) > +CFLAGS_REMOVE_lib/wc_neon_iowrite64_copy.o += $(CC_FLAGS_NO_FPU) You are spot on, I checked my patchset and the actual tested code (performance wise) beyond compilation used the following code: ifeq ($(ARCH),arm64)         CFLAGS_lib/neon_iowrite64_copy.o += -ffreestanding         CFLAGS_REMOVE_lib/neon_iowrite64_copy.o += -mgeneral-regs-only endif Which is actually equivalent to the diff you sent, Thanks for the heads-up will fix and resend. Thanks, Patrisious.