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 6DBFCC88E5C for ; Wed, 16 Sep 2026 14:03:55 +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=IptheR4vQDBIQxLkvesRjmvSsQ5ga6UjDiiO5KfeGL8=; b=2UXYirhK4xzOWD ZZ9Icnw1+PwHlrqdlt0WujAuMHxFzYcsAdq+Hw93KRAMSmo0w6I+8HhM0PaA86ANEAOAUXpKhtzFv kSmSNPATF5x54SW1XMjKPiOvKnDOmax4YwSmQKohpE+OekdEewAiy8A/Q/q2OroSyaX0u6MVp2Ae8 r209zBu111iUWfjoRJ+4+d06eS/MFhINUhU/HD97/O70s86Umf6jbY5hNvBe0kX++1P4POsJgMz04 djYv9XtxtlOIm9MLwv5KPiyymIZKldNNzEVGU19kI9GRj3q80uo1bPBCNLU71qJA7jMqHhYJ/IV1b 1ZukmmlSSFx3ptG5ZU8g==; Received: from localhost ([::1] helo=bombadil.infradead.org) by bombadil.infradead.org with esmtp (Exim 4.99.1 #2 (Red Hat Linux)) id 1x6qEe-00000009MRv-3j4T; Wed, 16 Sep 2026 14:03:41 +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 1x6qEc-00000009MRZ-20go; Wed, 16 Sep 2026 14:03:38 +0000 Received: from smtp.kernel.org (quasi.space.kernel.org [100.103.45.18]) by tor.source.kernel.org (Postfix) with ESMTP id 667BA60234; Wed, 16 Sep 2026 14:03:37 +0000 (UTC) Received: by smtp.kernel.org (Postfix) with ESMTPSA id 7105E1F000FF; Wed, 16 Sep 2026 14:03:24 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=kernel.org; s=k20260515; t=1789567417; bh=hO1YRILVaBOqm+dWq6qCTgxEbPpdVWHsaZacHfjUT/A=; h=Date:From:To:Cc:Subject:References:In-Reply-To; b=f7RWrddxO53t7XqQWGQqpP3lfBJi6WfPwofmEdM57qil6qIChEXUlmwKor5h6kBoa 9GtiaQGHN39ej2oq8F37LOrKCVhmvTOQjKW6hJb7MLQQEBdL7Wp00+3QWKwZvAomyS NoKwMiPOeftTdpj8xAtWPVc7gLXBtJhue+mreMUdP9rjPp5itv0EZmpo1EcFGFuaOg 6wBCD6BMMJuwTQfzHiqvbcCmwd3OrUYtvR6xVydAwVB94b6TjTf4NHDOAN6iJkQ1H5 JA+OYVYfyUjxkHRwB6C+LIyIx3AxkqaUGC2gvED56T6jLRNYsj01r7C5w9ImRppKs6 qi9QEBSo801MQ== Date: Wed, 16 Sep 2026 15:03:21 +0100 From: "Lorenzo Stoakes (ARM)" To: Gary Guo Cc: Kees Cook , 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 , =?utf-8?B?QmrDtnJu?= Roy Baron , Benno Lossin , Andreas Hindborg , Alice Ryhl , Trevor Gross , Danilo Krummrich , Daniel Almeida , Tamir Duberstein , Alexandre Courbot , Onur =?utf-8?B?w5Z6a2Fu?= , 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 20/21] kbuild: build rust crates in parallel with the rest of the build Message-ID: References: <20260914-build-speedup-v2-0-39817ec5db23@kernel.org> <20260914-build-speedup-v2-20-39817ec5db23@kernel.org> <202609141133.7CA979C89@keescook> MIME-Version: 1.0 Content-Disposition: inline In-Reply-To: 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 Wed, Sep 16, 2026 at 08:42:41AM +0100, Gary Guo wrote: > On Tue Sep 15, 2026 at 12:58 PM BST, Lorenzo Stoakes (ARM) wrote: > > On Mon, Sep 14, 2026 at 11:37:54AM -0700, Kees Cook wrote: > >> On Mon, Sep 14, 2026 at 10:22:19AM +0100, Lorenzo Stoakes (ARM) wrote: > >> > +# Rust code elsewhere in the tree depends upon rust/. > >> > +ifdef CONFIG_RUST > >> > +$(KBUILD_RUST_DIRS): | rust > >> > +endif > >> > [...] > >> > +export KBUILD_RUST_DIRS := drivers lib mm samples > >> > >> Doesn't this make all of drivers/, lib/, mm/ and samples/ wait for rust/? > >> That's a lot of stall: drivers/ is most of the tree. I think then a > >> CONFIG_RUST build has most of its C work waiting on the rust chain; > >> only the other top-level directories start early? This didn't create new > >> build delays for those configurations? > > > > Yeah good point. > > > > For a defconfig+rust clean build on 128 threads the other top-level directories > > were done at ~14s while rust ran to ~18.6s, so there was 4-5 of idle. > > > > However the patch improves things by net -3.9s regardless. > > > > This is really only a big box issue though. With fewer threads the rest of the > > tree takes longer so it has no impact on the build. > > > > (An aside - this kind of trade-off is what the series is all about really - the > > 'serial tail' - i.e. the single threaded stuff that _overlaps_ the end of the > > build is what slows you down.) > > > > Since this _still_ gives you a significant speed up on bigger boxes, I think > > it's fine as-is. > > > > The LLM says a fix for this would need significant work - a cross-instance lock > > and an on-demand rust/ build. So I think best as a follow-up? > > If we do it we're basically reinventing a new build system. Not saying that > Kbuild isn't one already :) :) I mean arguably make is a seriously limiting factor in improvements (the other might be... C headers... but that's a whole other kettle of fish ;) > > Best, > Gary > -- Cheers, Lorenzo _______________________________________________ linux-riscv mailing list linux-riscv@lists.infradead.org http://lists.infradead.org/mailman/listinfo/linux-riscv