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Mon, 30 Dec 2024 13:37:55 -0500 (EST) Date: Mon, 30 Dec 2024 10:37:24 -0800 From: Boqun Feng To: "Christoph Lameter (Ampere)" Cc: Mitchell Levy , Miguel Ojeda , Alex Gaynor , Gary Guo , =?iso-8859-1?Q?Bj=F6rn?= Roy Baron , Benno Lossin , Andreas Hindborg , Alice Ryhl , Trevor Gross , Andrew Morton , Dennis Zhou , Tejun Heo , linux-kernel@vger.kernel.org, rust-for-linux@vger.kernel.org, linux-mm@kvack.org Subject: Re: [PATCH RFC 3/3] rust: percpu: add a rust per-CPU variable test Message-ID: References: <20241219-rust-percpu-v1-0-209117e822b1@gmail.com> <20241219-rust-percpu-v1-3-209117e822b1@gmail.com> <5374de79-0ee6-e817-0f87-c800a6fbb733@gentwo.org> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <5374de79-0ee6-e817-0f87-c800a6fbb733@gentwo.org> X-Rspamd-Server: rspam10 X-Rspamd-Queue-Id: 753E7120019 X-Stat-Signature: j7ud5cf8u3etk349sdea17jbxr8odh7o X-Rspam-User: X-HE-Tag: 1735583823-304153 X-HE-Meta: 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 TF0l+spE 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 X-Bogosity: Unsure, tests=bogofilter, spamicity=0.496003, 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 Fri, Dec 20, 2024 at 09:56:54AM -0800, Christoph Lameter (Ampere) wrote: > On Thu, 19 Dec 2024, Mitchell Levy wrote: > > > + let mut native: i64 = 0; > > + let mut pcpu: PerCpuRef = unsafe { unsafe_get_per_cpu_ref!(PERCPU, CpuGuard::new()) }; > > A bit complex. > > > + native += -1; > > + *pcpu += -1; > > + assert!(native == *pcpu && native == -1); > > + > > + native += 1; > > + *pcpu += 1; > > + assert!(native == *pcpu && native == 0); > > + > > That's pretty straightforward..... But is there no symbolic access to the > per cpu namespace? How would you access the kernel per cpu variables > defined in C? > FWIW, there is a declare_extern_per_cpu!() marco in patch #1, and Mitchell used it to access this_cpu_off (defined in C). Maybe we want to see an example here? Regards, Boqun > How do you go about using per cpu atomics like > > this_cpu_inc(nr_dentry_unused); > >