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([174.127.224.194]) by smtp.gmail.com with ESMTPSA id d9443c01a7336-23abe426d82sm3689475ad.219.2025.06.26.11.50.30 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Thu, 26 Jun 2025 11:50:31 -0700 (PDT) Message-ID: <685d9677.170a0220.3b599c.7713@mx.google.com> X-Google-Original-Message-ID: Date: Thu, 26 Jun 2025 11:50:31 -0700 From: Mitchell Levy To: "Christoph Lameter (Ampere)" Cc: Miguel Ojeda , Alex Gaynor , Boqun Feng , Gary Guo , =?iso-8859-1?Q?Bj=F6rn?= Roy Baron , Andreas Hindborg , Alice Ryhl , Trevor Gross , Andrew Morton , Dennis Zhou , Tejun Heo , Danilo Krummrich , Benno Lossin , linux-kernel@vger.kernel.org, rust-for-linux@vger.kernel.org, linux-mm@kvack.org Subject: Re: [PATCH 4/5] rust: percpu: Add pin-hole optimizations for numerics References: <20250624-rust-percpu-v1-0-9c59b07d2a9c@gmail.com> <20250624-rust-percpu-v1-4-9c59b07d2a9c@gmail.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: X-Stat-Signature: 6f4a93yyaww634jefg8ay4bmekgjptxm X-Rspamd-Server: rspam05 X-Rspamd-Queue-Id: 16C351C0010 X-Rspam-User: X-HE-Tag: 1750963832-752621 X-HE-Meta: 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 mribnANu qZ32OOccbaxRDHuyMTROwP4pGnzfgBJQs50cXAhq6n2OYEIMJ/eB3BR1+evFQJEfX4akmeIUXKkVIV95/fCnVdSQByu/msql1OZRzmj0ulWqAsHFNodXHiUv7ZJRohD62lgreTKNsvNPA1Zclb29t3xbDPsbn3i6Fn9XgIZHP3H1DJCz6B2pknmPoEDK/ilKgJCkT/xzI4XQZ9J5kIpOjNGPFh9TXA7PEHzrf2Xc4+1EZT3LIQfyntnfTlwtFEs/EKYCMfq6De9aJE0i7wzse27+ANVyQckdlwcJctYn6XY9X+fG5moEPyyU9Ex4aTOEVpzmMX6LK7TkOKXRwsXrcZ3WSlEIE/RAa8G6gROjAf02mmjKiMPUzDcvMAFImn6tpc39kpPLcUQ16XLPGNoIMQWjPaRMcwtr6z9fqXFkL3sz6D0RlplIGrZp45ag7Q6uF46dXLxUb5OalVQ5mXis1jlHC3g== X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On Wed, Jun 25, 2025 at 10:21:17AM -0700, Christoph Lameter (Ampere) wrote: > On Tue, 24 Jun 2025, Mitchell Levy wrote: > > > The C implementations of `this_cpu_add`, `this_cpu_sub`, etc., are > > optimized to save an instruction by avoiding having to compute > > `this_cpu_ptr(&x)` for some per-CPU variable `x`. For example, rather > > than > > Cool. Great progress for Rust support. Maybe we can switch the SLUB > allocator over or come up with SLRB for the Slab Rust allocator ;-) Thank you! I'm certainly very excited about the prospect of more Rust :) > > > + impl PerCpuNumeric<'_, $ty> { > > + /// Adds `rhs` to the per-CPU variable. > > + pub fn add(&mut self, rhs: $ty) { > > + // SAFETY: `self.ptr.0` is a valid offset into the per-CPU area (i.e., valid as a > > + // pointer relative to the `gs` segment register) by the invariants of PerCpu. > > + unsafe { > > + asm!( > > + concat!("add gs:[{off}], {val}"), > > + off = in(reg) self.ptr.0 as *mut $ty, > > + val = in(reg_byte) rhs, > > That looks arch specific to x86? What about ARM and other platforms? Yes; pretty much everything added by this series is x86_64 specific. In `rust/kernel/lib.rs` the whole percpu module is gated behind `#[cfg(CONFIG_X86_64)]`. I'm certainly interested in adding support for ARM and other architectures. That said, x86 is where I started, and since it's in a workable state, I wanted to get some input from the list.