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[103.168.172.201]) by smtp.gmail.com with ESMTPSA id af79cd13be357-7c958cbd21dsm770844485a.42.2025.04.29.12.28.01 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Tue, 29 Apr 2025 12:28:01 -0700 (PDT) Message-ID: <68112841.050a0220.17967c.3236@mx.google.com> X-Google-Original-Message-ID: Received: from phl-compute-01.internal (phl-compute-01.phl.internal [10.202.2.41]) by mailfauth.phl.internal (Postfix) with ESMTP id C96E5120006A; Tue, 29 Apr 2025 15:28:00 -0400 (EDT) Received: from phl-mailfrontend-01 ([10.202.2.162]) by phl-compute-01.internal (MEProxy); Tue, 29 Apr 2025 15:28:00 -0400 X-ME-Sender: X-ME-Received: X-ME-Proxy-Cause: gggruggvucftvghtrhhoucdtuddrgeefvddrtddtgddvieegieehucetufdoteggodetrf dotffvucfrrhhofhhilhgvmecuhfgrshhtofgrihhlpdggtfgfnhhsuhgsshgtrhhisggv pdfurfetoffkrfgpnffqhgenuceurghilhhouhhtmecufedttdenucesvcftvggtihhpih gvnhhtshculddquddttddmnecujfgurhepfffhvfevuffkfhggtggujgesthdtredttddt vdenucfhrhhomhepuehoqhhunhcuhfgvnhhguceosghoqhhunhdrfhgvnhhgsehgmhgrih hlrdgtohhmqeenucggtffrrghtthgvrhhnpefhtedvgfdtueekvdekieetieetjeeihedv teehuddujedvkedtkeefgedvvdehtdenucffohhmrghinhepkhgvrhhnvghlrdhorhhgne cuvehluhhsthgvrhfuihiivgeptdenucfrrghrrghmpehmrghilhhfrhhomhepsghoqhhu nhdomhgvshhmthhprghuthhhphgvrhhsohhnrghlihhthidqieelvdeghedtieegqdduje ejkeehheehvddqsghoqhhunhdrfhgvnhhgpeepghhmrghilhdrtghomhesfhhigihmvgdr nhgrmhgvpdhnsggprhgtphhtthhopeegtddpmhhouggvpehsmhhtphhouhhtpdhrtghpth htoheprghrnhgusegrrhhnuggsrdguvgdprhgtphhtthhopehfuhhjihhtrgdrthhomhho nhhorhhisehgmhgrihhlrdgtohhmpdhrtghpthhtoheprgdrhhhinhgusghorhhgsehkvg hrnhgvlhdrohhrghdprhgtphhtthhopehruhhsthdqfhhorhdqlhhinhhugiesvhhgvghr rdhkvghrnhgvlhdrohhrghdprhgtphhtthhopehgrghrhiesghgrrhihghhuohdrnhgvth dprhgtphhtthhopegrlhhitggvrhihhhhlsehgohhoghhlvgdrtghomhdprhgtphhtthho pehmvgeskhhlohgvnhhkrdguvghvpdhrtghpthhtohepuggrnhhivghlrdgrlhhmvghiug grsegtohhllhgrsghorhgrrdgtohhmpdhrtghpthhtoheplhhinhhugidqkhgvrhhnvghl sehvghgvrhdrkhgvrhhnvghlrdhorhhg X-ME-Proxy: Feedback-ID: iad51458e:Fastmail Received: by mail.messagingengine.com (Postfix) with ESMTPA; Tue, 29 Apr 2025 15:27:59 -0400 (EDT) Date: Tue, 29 Apr 2025 12:27:59 -0700 From: Boqun Feng To: Arnd Bergmann Cc: FUJITA Tomonori , Andreas Hindborg , rust-for-linux@vger.kernel.org, Gary Guo , Alice Ryhl , me@kloenk.dev, daniel.almeida@collabora.com, linux-kernel@vger.kernel.org, Netdev , Andrew Lunn , Heiner Kallweit , Trevor Gross , Miguel Ojeda , Alex Gaynor , =?iso-8859-1?Q?Bj=F6rn?= Roy Baron , Benno Lossin , Andreas Hindborg , Anna-Maria Gleixner , Frederic Weisbecker , Thomas Gleixner , John Stultz , Stephen Boyd , Ingo Molnar , Peter Zijlstra , Juri Lelli , Vincent Guittot , Dietmar Eggemann , Steven Rostedt , Benjamin Segall , Mel Gorman , Valentin Schneider , tgunders@redhat.com, david.laight.linux@gmail.com, Paolo Bonzini , Jocelyn Falempe , Russell King , Christian Schrefl , Linus Walleij Subject: Re: [PATCH v15 5/6] rust: time: Add wrapper for fsleep() function References: <6qQX4d2uzNlS_1BySS6jrsBgbZtaF9rsbHDza0bdk8rdArVf_YmGDTnaoo6eeNiU4U_tAg1-RkEOm2Wtcj7fhg==@protonmail.internalid> <20250423192857.199712-6-fujita.tomonori@gmail.com> <871ptc40ds.fsf@kernel.org> <20250429.221733.2034231929519765445.fujita.tomonori@gmail.com> <5c18acfc-7893-4731-9292-dc69a7acdff2@app.fastmail.com> <1b9e8761-b71f-4015-bf7d-29072b02f2ac@app.fastmail.com> <6811092a.050a0220.27f104.5603@mx.google.com> <2d89292f-b02c-47b1-9299-92c5f4ba4c9d@app.fastmail.com> <681124ff.050a0220.13a0e7.2c80@mx.google.com> Precedence: bulk X-Mailing-List: netdev@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <681124ff.050a0220.13a0e7.2c80@mx.google.com> On Tue, Apr 29, 2025 at 12:14:04PM -0700, Boqun Feng wrote: > On Tue, Apr 29, 2025 at 08:33:47PM +0200, Arnd Bergmann wrote: > > On Tue, Apr 29, 2025, at 19:15, Boqun Feng wrote: > > > On Tue, Apr 29, 2025 at 06:11:02PM +0200, Arnd Bergmann wrote: > > >> On Tue, Apr 29, 2025, at 18:03, Boqun Feng wrote: > > > > > > Would it make sense if we rely on compiler optimization when it's > > > avaiable (for x86_64, arm64, riscv, etc), and only call ktime_to_ms() if In case I wasn't clear, nowadays Rust compiler supports optimizating constant division into multi/shift on x86_64, arm64, riscv already, the optimization is only not availabe for arm32. (It's actually an optimization provided by LLVM I think) Regards, Boqun > > > not? The downside of calling ktime_to_ms() are: > > > > > > * it's a call function, and cannot be inlined with LTO or INLINE_HELPER: > > > > > > https://lore.kernel.org/all/20250319205141.3528424-1-gary@garyguo.net/ > > > > > > * it doesn't provide the overflow checking even if > > > CONFIG_RUST_OVERFLOW_CHECKS=y > > > > > > Thoughts? > > > > The function call overhead is tiny compared to replacing a 64-bit > > division with a constant mult/shift. > > > > Just to be clear, are you essientially saying that even in C, > ktime_to_ms() is not worth inlining? Because the call overhead is tiny > compared to the function own cost? > > My impression is that on x86 at least, function call is 10+ cycles, and > multiply is 3 cycles, so I would think that ktime_to_ms() itself is at > most 10 cycles. Maybe I'm out of date of the modern micro-architecture? > > > What is the possible overflow that can happen here? For a constant > > division at least there is no chance of divide-by-zero. Do you mean > > truncating to 32 bit? > > > > I was referring the last part of Miguel's email: > > https://lore.kernel.org/rust-for-linux/CANiq72mMRpY4NC4_8v_wDpq6Z3qs99Y8gXd-7XL_3Bed58gkJg@mail.gmail.com/ > > Regards, > Boqun > > > Arnd