From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from smtp.kernel.org (aws-us-west-2-korg-mail-alma10-1.taild15c8.ts.net [100.103.45.18]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 2F0C6577E49; Wed, 9 Sep 2026 14:26:43 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=100.103.45.18 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1788964005; cv=none; b=WRoyaqM1b/PlWqwnNaiMrNEkhjknI07b1U6T7qHXI0ircY2DP/EgvsVgjl1QKXP5TjbubgjmKXso99qD4yoLPXQoel0Hb85TcWDxSKmpHqb+48WKPVn5GSgiHnVlY3ZpdVz+sQVPVcd04RgNt3yBwNUPVYAtcoX36lEpDjCHcvU= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1788964005; c=relaxed/simple; bh=gic5TB1gjIu6RSleeqefVviRlVsBU2B+Giz1F9TOV84=; h=Date:From:To:Cc:Subject:Message-ID:References:MIME-Version: Content-Type:Content-Disposition:In-Reply-To; b=dtuhUtDytp44y6oUezukNcuYCRaf7jg/V1Sj3yNunir/RfITnoHQlH46rb1IamXpc70ie5y13LUhIfQcKW8WlsrwW74ieeqfOaOtoxzlIU6/yAjilCvBIc1vDT5O3DQ2I/jXjncVx+25xRP+7cMzFaMsC2dUJjGiyBpPiSPvIOU= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=hJGsxqSP; arc=none smtp.client-ip=100.103.45.18 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b="hJGsxqSP" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 5935C1F00A3E; Wed, 9 Sep 2026 14:26:32 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=kernel.org; s=k20260515; t=1788964003; bh=gic5TB1gjIu6RSleeqefVviRlVsBU2B+Giz1F9TOV84=; h=Date:From:To:Cc:Subject:References:In-Reply-To; b=hJGsxqSPGASMshdRSJCdjqaV2MTHzCBOelFMCkNds3SUKI1cp6lgYYL9WvlWqpKiY u+Kr8fJtqUm+2F0r5r+yWto5EILdK28AmJteGlYqyv06gteJ/wga1IEVp7sbb09ZMa nDUytFsFJVzuptuOydFiRQr9qOr4s+rVgAcsjl1yHrkj9q81/ZBU8Q4w71vItIdb7Q 6FKrgP0eG1rOEQkj4gVKSakS0M+h2v/B/FCSAMQ+KSwhdA7w5QK8j1eIsAjVFXEOpa ot1NILoh0llV+mv2GC1wRWyTS2CYE2y9cXqBghpj95qgm3Bs0kubAcZIAqnS0JByoE cjOuGdB7tC82A== Date: Wed, 9 Sep 2026 15:26:29 +0100 From: "Lorenzo Stoakes (ARM)" To: Miguel Ojeda Cc: =?utf-8?B?QmrDtnJu?= Baron , 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 , 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 , 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 Subject: Re: [PATCH 20/23] kbuild: rust: parallelise rustc front end Message-ID: References: <20260908-build-speedup-v1-0-5dc1ac01672d@kernel.org> <20260908-build-speedup-v1-20-5dc1ac01672d@kernel.org> Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: On Wed, Sep 09, 2026 at 02:59:13PM +0200, Miguel Ojeda wrote: > On Wed, Sep 9, 2026 at 12:22 PM Björn Baron wrote: > > > > There are still several known reproducibility issues for the parallel > > frontend[1] and at least until fairly recently there were also deadlock > > issues and incorrect errors[2], so I would not recommend enabling it without > > an explicit request from the user. Perhaps even only allow it on nightly > > rustc for now, then you don't need to check which of the two spellings of > > the flag is supported. > > Thanks a lot for taking a look Björn. > > If there are still major issues even in nightly, then I would say > let's not add it yet -- some users/CIs are testing with nightly > routinely, so it is probably best to avoid surprises for them. (If > someone wants to test the flag, they can still pass it manually.) > > On the other hand, if there are no major issues left and it is just > reproducibility issues, then I guess we could add it to help figure > those issues out and avoid surprises later on. Yup, I am encouraged by 'until fairly recently' on that ;) so maybe just bump version requirement to whatever this recently was? > > > By the way, currently backend parallelism is entirely disabled due to the > > usage of --emit obj (which forces -Ccodegen-units=1). For -O2/3 builds > > Yeah, we even set `-Ccodegen-units=1` explicitly at the moment, so we > would need to change that too (and likely make it an option, because > normally end users will want the best results, while developers may > want speed of iteration). > > Cheers, > Miguel -- Cheers, Lorenzo