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[82.69.66.36]) by smtp.gmail.com with ESMTPSA id ffacd0b85a97d-47fb6aa3a88sm1967617f8f.6.2026.07.28.14.47.56 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Tue, 28 Jul 2026 14:47:56 -0700 (PDT) Date: Tue, 28 Jul 2026 22:47:55 +0100 From: David Laight To: Mark Rutland Cc: linux-arm-kernel@lists.infradead.org, ada.coupriediaz@arm.com, ardb@kernel.org, catalin.marinas@arm.com, hca@linux.ibm.com, linux-kernel@vger.kernel.org, maz@kernel.org, peterz@infradead.org, ruanjinjie@huawei.com, vladimir.murzin@arm.com, will@kernel.org, yang@os.amperecomputing.com Subject: Re: [RFC PATCH 07/13] arm64: percpu: Implement preemptible read/write ops Message-ID: <20260728224755.59cfd22d@pumpkin> In-Reply-To: <20260728123859.2911495-8-mark.rutland@arm.com> References: <20260728123859.2911495-1-mark.rutland@arm.com> <20260728123859.2911495-8-mark.rutland@arm.com> X-Mailer: Claws Mail 4.1.1 (GTK 3.24.38; arm-unknown-linux-gnueabihf) Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit On Tue, 28 Jul 2026 13:38:53 +0100 Mark Rutland wrote: > Use the PCPU GPR infrastructure to implement preemptible this_cpu_read() > and this_cpu_write(). ... > #define this_cpu_write_1(pcp, val) \ > - _pcp_protect(__percpu_write_8, pcp, (unsigned long)val) > + _pcp_wrap(__percpu_write_8, pcp, (unsigned long)val) Not new, but does that end up sign extending 'val' which is likely to be more expensive than zero extending it? Using '(val) + 0u + 0ul' might generate better code in some cases. Just noticed it should be (unsigned long)(val) as well. Otherwise this_cpu_write_n(pcp, -7 / 4) isn't going to DTRT. David > #define this_cpu_write_2(pcp, val) \ > - _pcp_protect(__percpu_write_16, pcp, (unsigned long)val) > + _pcp_wrap(__percpu_write_16, pcp, (unsigned long)val) > #define this_cpu_write_4(pcp, val) \ > - _pcp_protect(__percpu_write_32, pcp, (unsigned long)val) > + _pcp_wrap(__percpu_write_32, pcp, (unsigned long)val) > #define this_cpu_write_8(pcp, val) \ > - _pcp_protect(__percpu_write_64, pcp, (unsigned long)val) > + _pcp_wrap(__percpu_write_64, pcp, (unsigned long)val) > > #define this_cpu_add_1(pcp, val) \ > _pcp_protect(__percpu_add_case_8, pcp, val)