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Tue, 15 Sep 2026 14:03:29 -0400 (EDT) X-Mailer: MessagingEngine.com Webmail Interface Precedence: bulk X-Mailing-List: linux-arch@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 X-ThreadId: ArHA-gVR6p-N Date: Tue, 15 Sep 2026 20:02:38 +0200 From: "Arnd Bergmann" To: "Nick Desaulniers" , "Kees Cook" Cc: "Lorenzo Stoakes" , "Linus Torvalds" , "Nathan Chancellor" , "Nicolas Schier" , "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" , "Catalin Marinas" , "Will Deacon" , "Mark Rutland" , "Ard Biesheuvel" , "Ilias Apalodimas" , "Josh Poimboeuf" , "Peter Zijlstra" , "Miguel Ojeda" , "Boqun Feng" , "Gary Guo" , =?UTF-8?Q?Bj=C3=B6rn_Roy_Baron?= , "Benno Lossin" , "Andreas Hindborg" , "Alice Ryhl" , "Trevor Gross" , "Danilo Krummrich" , "Daniel Almeida" , "Tamir Duberstein" , "Alexandre Courbot" , =?UTF-8?Q?Onur_=C3=96zkan?= , "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 , 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 Message-Id: <90006ad1-73df-4bd0-a434-61875edd5bb9@app.fastmail.com> In-Reply-To: References: <20260914-build-speedup-v2-0-39817ec5db23@kernel.org> <20260914-build-speedup-v2-21-39817ec5db23@kernel.org> <202609140844.FA7E848A@keescook> <202609150955.A51C9F7A20@keescook> Subject: Re: [PATCH v2 21/21] kbuild: use pigz for gzip compression if available Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: quoted-printable On Tue, Sep 15, 2026, at 19:47, Nick Desaulniers wrote: > On Tue, Sep 15, 2026 at 10:31=E2=80=AFAM Kees Cook w= rote: >> On Tue, Sep 15, 2026 at 03:30:43PM +0100, Lorenzo Stoakes (ARM) wrote: >> a) >> My main concern is the lack of respecting the -j make argument. In my >> mind, this is a blocker, because it means a build will now _always_ s= pin >> up max CPUs (not what -j has limited it to), and for CIs, shared comp= ute >> systems, or whatever, this violates the requested parallelism level. = For >> example, if I'm doing a long-running Coccinelle replacement in one tr= ee >> (which uses half the CPUs), any builds I launch I'm asking for the ot= her >> half of my CPUs to be used so they don't thrash my cache. >> >> This is the kind of "why are all the CPUs spinning up?" question I >> helped track down with commit 51e46c7a4007 ("docs, parallelism: Rearr= ange >> how jobserver reservations are made") forever ago. > > Parse -j from MAKEFLAGS (https://stackoverflow.com/a/76517886), > forward it to pigz? That still has a potential O(n=C2=B2) problem: if one builds N kernels with a top-level jobserver on N CPUs, and they all take the same amount of time, you end up with N pigz processes each trying to use N cpus at the same time. Ideally we'd use the equivalent of -flto=3Dauto in the compiler, which respects jobserver settings, but I don't think pigz supports this at the moment. Arnd