From mboxrd@z Thu Jan 1 00:00:00 1970 Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.remote-ip=90.155.50.34 ARC-Seal: i=1; d=subspace.kernel.org; s=arc20261015; a=rsa-sha256; cv=none; t=1794496079; b=2Ju2MDpGMO6oen/h9HR07OaAlDyuDqKbTCz8wTFHSX5ip6LGP0Dcj1hA65PsrkDvAoot wlatFsqKhNA12z08In6T0Pfa7ty4rzHGkXv81BBUzJpEP3FM8asF5vstnXgMGu4MG+Zb6 qtDFvpR4hdOBZMgGzq8FEeViPDnIfdwKRL1Wk+IZ0f5iAnbNUNoDHUGYq3s/2SQAi4ZLU 0qvZWOr0cd6fl/WoOLLtecubGm7h3PqfwDFyLRm+IwEK+oVg5QJCj0lVzMSSDBhh2Mt5q /Ae/sHBciqxHz0KuHrTGrfkv0rhGrXwWtVsNmscPdwU/f1fNvxhhvlo7128wa5GF3xA== ARC-Message-Signature: i=1; d=subspace.kernel.org; s=arc20261015; a=rsa-sha256; c=relaxed/relaxed; t=1794496079; h=DMARC-Filter:DKIM-Signature:Received:Received:Date:From:To:Cc: Subject:Message-ID:References:MIME-Version:Content-Type: Content-Disposition:In-Reply-To; bh=6opaRvcpYR6ER81jsMzDjvR9PJZQhTjt+6UYrb+STEQ=; b=nTSJAlH2BR5YjapnrY9JCf334Com3lm7slf92xTA0fZxCOEoQQoVNjX1B9pMVJFHBGlW iFURGPBvLCkP3zxCd1hOv2y8xFygZqBJ0AGMODmnMNhcFIsXQpUukAKOabzu9uL72pGMX whArDijOmlHQ0Km3yTGVBMSPV/TPtN3HQgZXoqJcp8P3Ya/BFH53ysLS+nLUOysVwbp3N A3Pbj9TvzaTtDDVY7yC1kLjGgcRQHLiBK8CuynXF4s46QZBZFRAB7AHp6YVWhgZ1I3oqW /wzbu/BuOW3KZUOtPTGOuCCl8UlSylkLENoZbrQ5Hml0cys5cxIVlo16sXTcDR37Z4g== ARC-Authentication-Results: i=1; smtp.subspace.kernel.org; dmarc=pass header.from=infradead.org; spf=pass smtp.mailfrom=infradead.org; dkim=pass header.d=infradead.org header.i=@infradead.org header.a=rsa-sha256 header.s=casper.20170209 header.b=XKFkU1s1; arc=none smtp.remote-ip=90.155.50.34 Received: from casper.infradead.org (casper.infradead.org [90.155.50.34]) (using TLSv1.3 with cipher TLS_AES_256_GCM_SHA384 (256/256 bits) key-exchange X25519 server-signature ECDSA (prime256v1) server-digest SHA256) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id DA9B7606A330; Thu, 12 Nov 2026 15:07:58 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.4.2 smtp.subspace.kernel.org DA9B7606A330 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=infradead.org Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=infradead.org Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=infradead.org header.i=@infradead.org header.a=rsa-sha256 header.s=casper.20170209 header.b=XKFkU1s1 DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=infradead.org; s=casper.20170209; h=In-Reply-To:Content-Type:MIME-Version: References:Message-ID:Subject:Cc:To:From:Date:Sender:Reply-To: Content-Transfer-Encoding:Content-ID:Content-Description; bh=6opaRvcpYR6ER81jsMzDjvR9PJZQhTjt+6UYrb+STEQ=; b=XKFkU1s1WLuQPbtURXoArtJ7j7 o9pwHo3e6AdR8Zgtb6oRujApHL3gysKUnm6lDE0R7s1iTknyaH74HuyPtjCmuEoIGR3T+kN23iBZ/ KlC8uFl6aqsVrqrxFqFnM5qZQtQR+WRpfY7ztO0HcKJKXGWlRTCs/Y8GwaDEVsUt8sXtElrY1Gp5f uACRXsOItxvIZI7gScaYKe66Qxz8TJE5h1mZ6Thk3x0sk28ZJmbOjryXKSMUK7zjjSn7aaN3r8lOG q6ISBbgwj1rpG85dXSwLafePK2XjQK1CNNQ7Y+S3vUAsU2M3nNQuw5l9OUmUQ8djIDj4r0kubq30z 9X5y0OfA==; Received: from 77-249-17-252.cable.dynamic.v4.ziggo.nl ([77.249.17.252] helo=noisy.programming.kicks-ass.net) by casper.infradead.org with esmtpsa (Exim 4.100.1 #2 (Red Hat Linux)) id 1xRWP0-00000008PHw-0kFR; Thu, 12 Nov 2026 15:07:50 +0000 Received: by noisy.programming.kicks-ass.net (Postfix, from userid 1000) id 42E64302FBC; Thu, 12 Nov 2026 16:07:49 +0100 (CET) Date: Thu, 12 Nov 2026 16:07:49 +0100 From: Peter Zijlstra To: Steven Rostedt Cc: Huacai Chen , Huacai Chen , Andrew Morton , Ingo Molnar , Juri Lelli , Vincent Guittot , Dietmar Eggemann , Ben Segall , Mel Gorman , linux-mm@kvack.org, linux-kernel@vger.kernel.org, stable@vger.kernel.org, Tiezhu Yang Subject: Re: [PATCH] lib/smp_processor_id: Don't warn if there is only one CPU Message-ID: <20261112150749.GA1813469@noisy.programming.kicks-ass.net> References: <20261111092421.3771992-1-chenhuacai@loongson.cn> <20261111170600.GS1779021@noisy.programming.kicks-ass.net> <20261112081348.GB2668804@noisy.programming.kicks-ass.net> <20261112094059.18f66c2a@fedora> X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Post: List-Help: List-Subscribe: List-Unsubscribe: List-Owner: Precedence: list MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20261112094059.18f66c2a@fedora> On Thu, Nov 12, 2026 at 09:40:59AM -0500, Steven Rostedt wrote: > On Thu, 12 Nov 2026 09:13:48 +0100 > Peter Zijlstra wrote: > > > num_possible_cpus() is what I was thinking of. Notably, there is no > > requirement that the CPU bitmap is dense. You can have nr_cpu_ids at 256 > > and use 255 for your boot CPU. It would be completely daft to do so, but > > it is still valid. > > Hmm, I was under the impression that there would always be a CPU 0. > > Is it possible to boot with a non zero CPU setup? Yes. Voyager did that -- although that code is now long gone. In general we must not assume boot cpu is 0 -- although I don't know of any architecture that currently doesn't have that. Might be fun to have it as a debug option to catch out assumptions.