From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org Received: from bombadil.infradead.org (bombadil.infradead.org [198.137.202.133]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.lore.kernel.org (Postfix) with ESMTPS id 29EDEC88E72 for ; Mon, 14 Sep 2026 18:32:33 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=lists.infradead.org; s=bombadil.20210309; h=Sender: Content-Transfer-Encoding:Content-Type:List-Subscribe:List-Help:List-Post: List-Archive:List-Unsubscribe:List-Id:In-Reply-To:MIME-Version:References: Message-ID:Subject:Cc:To:From:Date:Reply-To:Content-ID:Content-Description: Resent-Date:Resent-From:Resent-Sender:Resent-To:Resent-Cc:Resent-Message-ID: List-Owner; bh=sitG1gGPj9vvvbVD4S6T2Nny0qI+AsKSU4PXi7sT0IM=; b=CHr0zxh92cicHV 6+GHyCb+4XgmZmyZcvSCIJMQkbXPGl3+SKUpWkyx6huvt5MCuIkI+QEJVHGqTjaO0FvznuCuqWcr1 ZYKytZOf4alDrg7qH7PUyLm9BL3d8TXS8H3gfzXS9yCesuIKIo96jbrPA8zHGvO6YaNyYw095wkev 6VH+E3KoLiSDpJTFOnU1l3veIPM1Yv+qqoNc4wF4pJRvYfAYeLZUJ/1BkX0ydR+lZ5nENGnUBH2in u/PjcPZ27Xv3iCMtggQpNpkFE1PxLlVPJptwpMbjKrC5gIkhlDg0KFqoLz4+mJSLRJKwIwkU+Wwqg 2xIW7YYb2EYV7pgGRbcA==; Received: from localhost ([::1] helo=bombadil.infradead.org) by bombadil.infradead.org with esmtp (Exim 4.99.1 #2 (Red Hat Linux)) id 1x6BTW-00000004S3E-1E61; Mon, 14 Sep 2026 18:32:19 +0000 Received: from tor.source.kernel.org ([2600:3c04:e001:324:0:1991:8:25]) by bombadil.infradead.org with esmtps (Exim 4.99.1 #2 (Red Hat Linux)) id 1x6BTU-00000004S2y-0j8z; Mon, 14 Sep 2026 18:32:16 +0000 Received: from smtp.kernel.org (quasi.space.kernel.org [100.103.45.18]) by tor.source.kernel.org (Postfix) with ESMTP id 3B1686022A; Mon, 14 Sep 2026 18:32:15 +0000 (UTC) Received: by smtp.kernel.org (Postfix) with ESMTPSA id D5DB41F00893; Mon, 14 Sep 2026 18:32:14 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=kernel.org; s=k20260515; t=1789410734; bh=qh1ZerciXS6mhhgUbgOWtjBtb3wIfa62KF3pRdi9HRg=; h=Date:From:To:Cc:Subject:References:In-Reply-To; b=LT1cFNgkvbD3eoVT/UaBEH3+r1ZmImzoNjg1sB0fKgYfiWphX+2k3leDEJjTKPvkI UCeZKsCtpOsU1Qh6ZRgd9PGKscvkwgEZ/CXkgLZsggzcTd3LcxREE5AMbc7rSZ176a 7gNUxLvYBfZ5rTEMblheppVavtWDrYGJ9aihGEv2SwKX80uE2nVnkBoFYyryneR1eY l99LJZaV59sYUO8uU85RDxazHEX6uhwHzX4FGdH4s0ESmZYKyjLD5malFkq7HqRZYp MO93SpFQpfLWTJCfXhlr1iU+iBNmOcV7d+vp6+IkNPD3Hj/IjfJ9MaHA5ebXh1WWUJ +Cz7fAfk/ogdA== Date: Mon, 14 Sep 2026 11:32:14 -0700 From: Kees Cook To: "Lorenzo Stoakes (ARM)" Cc: Linus Torvalds , Nathan Chancellor , Nicolas Schier , Nick Desaulniers , Bill Wendling , Justin Stitt , Masahiro Yamada , Alexey Gladkov , Thomas Gleixner , Ingo Molnar , Borislav Petkov , Dave Hansen , x86@kernel.org, "H. Peter Anvin" , Paul Walmsley , Palmer Dabbelt , Albert Ou , Alexandre Ghiti , Arnd Bergmann , Catalin Marinas , Will Deacon , Mark Rutland , Ard Biesheuvel , Ilias Apalodimas , Josh Poimboeuf , Peter Zijlstra , Miguel Ojeda , Boqun Feng , Gary Guo , =?iso-8859-1?Q?Bj=F6rn?= Roy Baron , Benno Lossin , Andreas Hindborg , Alice Ryhl , Trevor Gross , Danilo Krummrich , Daniel Almeida , Tamir Duberstein , Alexandre Courbot , Onur =?iso-8859-1?Q?=D6zkan?= , Jonathan Corbet , Randy Dunlap , "Gustavo A. R. Silva" , linux-kbuild@vger.kernel.org, linux-kernel@vger.kernel.org, llvm@lists.linux.dev, linux-riscv@lists.infradead.org, linux-arch@vger.kernel.org, linux-arm-kernel@lists.infradead.org, linux-efi@vger.kernel.org, rust-for-linux@vger.kernel.org, linux-doc@vger.kernel.org, Jens Axboe , linux-hardening@vger.kernel.org Subject: Re: [PATCH v2 18/21] kbuild: rust: optionally parallelise rustc front end Message-ID: <202609141124.F24B6F77@keescook> References: <20260914-build-speedup-v2-0-39817ec5db23@kernel.org> <20260914-build-speedup-v2-18-39817ec5db23@kernel.org> MIME-Version: 1.0 Content-Disposition: inline In-Reply-To: <20260914-build-speedup-v2-18-39817ec5db23@kernel.org> X-BeenThere: linux-riscv@lists.infradead.org X-Mailman-Version: 2.1.34 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Sender: "linux-riscv" Errors-To: linux-riscv-bounces+linux-riscv=archiver.kernel.org@lists.infradead.org On Mon, Sep 14, 2026 at 10:22:17AM +0100, Lorenzo Stoakes (ARM) wrote: > The threads are taken from make's jobserver, so a parallel build is not > oversubscribed. It was found that benefits level off at 8 threads (16 was > found to be around the same, and 32 slower). I think it's worth noting that this comes from rustc itself (it has built-in support for the make jobserver). See commit ecab4115c44c ("kbuild: mark `rustc` (and others) invocations as recursive"). What happens when there is no jobserver, e.g. "make" without -j, or "make -j1"? > [...] > rustc has a parallel front end, enabled with -Zthreads, available since > rust 1.84 [0] and therefore on every rustc the kernel supports. > > It is not yet stable and its output is not reproducible, so it cannot be > [...] > +The number of threads rustc's parallel front end may use, passed to it as > +``-Zthreads``. Unset by default, as the parallel front end is not yet > +stable and its output is not reproducible. The gain levels off at 8 > +threads. Okay, unstable, not reproducible. > Generated output was confirmed byte-for-byte identical. But this says otherwise? I am confused. Reproducible or not? -- Kees Cook _______________________________________________ linux-riscv mailing list linux-riscv@lists.infradead.org http://lists.infradead.org/mailman/listinfo/linux-riscv