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 C19DCC55162 for ; Thu, 30 Jul 2026 15:50:32 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=lists.infradead.org; s=bombadil.20210309; h=Sender:List-Subscribe:List-Help :List-Post:List-Archive:List-Unsubscribe:List-Id:In-Reply-To: Content-Transfer-Encoding:Content-Type: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=slh2h9i6LmNp2WolpBB5Yw2Tk8/zNA233qAcOw9cOEU=; b=J0FXNSIEJT1ZPYMR39v3W9n8k6 3T6v0T84f8UTIKqdSNMEGXSaqD/NcTYl2gW9CaeDo6rb3k2nwlawBwob1OPk6B3ugrMTqlfufdpwK e4XCqcqmMteyZBKW9i2YSfJXn9hes4f57q6OrDI+fjnuEZ9sxbvlSERtYh/1PhroY74fS6D7IUedZ iJ0As+yiHJo9pOH3zC6zyz1K1hLPvnOZbebvH8R18ThpSyGTlX2ubDFm6mStECgBXmGcOo03ejHWY o1GATtBzOgQOH+0895IuLMBNYFZovLvG/F8XfnsFScIPf1EBMmZmHbagz6epm68EU3jfww8aAmOR1 lbGHnAIw==; Received: from localhost ([::1] helo=bombadil.infradead.org) by bombadil.infradead.org with esmtp (Exim 4.99.1 #2 (Red Hat Linux)) id 1wpT1f-0000000Asu5-3LUH; Thu, 30 Jul 2026 15:50:27 +0000 Received: from sea.source.kernel.org ([2600:3c0a:e001:78e:0:1991:8:25]) by bombadil.infradead.org with esmtps (Exim 4.99.1 #2 (Red Hat Linux)) id 1wpT1Z-0000000Assk-1iIR for kexec@lists.infradead.org; Thu, 30 Jul 2026 15:50:25 +0000 Received: from smtp.kernel.org (quasi.space.kernel.org [100.103.45.18]) by sea.source.kernel.org (Postfix) with ESMTP id BBD5542088; Thu, 30 Jul 2026 15:50:20 +0000 (UTC) Received: by smtp.kernel.org (Postfix) with ESMTPSA id EF7271F00A3A; Thu, 30 Jul 2026 15:50:19 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=kernel.org; s=k20260515; t=1785426620; bh=slh2h9i6LmNp2WolpBB5Yw2Tk8/zNA233qAcOw9cOEU=; h=Date:From:To:Cc:Subject:References:In-Reply-To; b=du3CuQn5FbJjj+PuyjCv0FBKJmUIuzG4wTQztDWdjUZP9g/0obSKrgMM+2b501jZm WftRskHQri4dB7OGEH/4ukCwaJXv4MX2Kbtsyj7hnkwQVAbVewFthh9Nl21acJ3NaY 0kEKtOMjaeqtAlEgt9l5c9m9vkM7UaOR/KF6yKkjrlmlWs9TO+nGnZpm+Sb1Hp/5dK 1eWqZXCJY/oLFrL2pq8gVibSaaEmnx0HNkIr1NJKN525f6Z7RXXVHU8HoQJc9PmRyi +2g1pq5izPWNK7ybkmHUqIhkI6IQXhlSqiBvvmL3XdiMWkYexaA/QcRG+oiRk0mjAH HxgBYMnJJrk0A== Received: from phl-compute-05.internal (phl-compute-05.internal [10.202.2.45]) by mailfauth.phl.internal (Postfix) with ESMTP id 1F9B2F4008A; Thu, 30 Jul 2026 11:50:19 -0400 (EDT) Received: from phl-frontend-04 ([10.202.2.163]) by phl-compute-05.internal (MEProxy); Thu, 30 Jul 2026 11:50:19 -0400 X-ME-Sender: X-ME-Received: X-ME-Proxy-Cause: dmFkZTFFxRhh5KtXZvMKng+4z/FIbdoeZvQuEFFHsoNeHQ+UNAcs3VBtxuRHLSDm37bIOn oUuzCNuNSwrs7M3kDoMbUWv+JBMVKNQUBaHC/EV1u4MGvMVIdDMskyKWqDAeZEr5Fpvt1z JonHD4tHPtT0T76ZjAKAxEDO6ycApw5+Kb35yY4OD+zCcJh8JxYFoxWZ7dqcw3RNMTjGxS 1HoztlSoTAMW8OF+c70eYl8eih37WQriL9x51T+OB5tx485FCEtTtfe6HXB/R5eNgrDOOK BFY0X/K69HagfQ2jACUpCOUig+0JKtQXkbcQnkKMxa9iVfntYF4tTR1rMQ7SBHZadmZcFU MaeJsLoxLRmyvtLIZPjxfzlUGxdCd3AOeCw6qHCbpaOI1Cen20GIX8GMfzfs0zt5eslK1X Gclm0SvSCO9I4e0wNCMeF3MS21A5AXTyNq64AA4i4KeUYmElqxdzyCSGNAJ51xudbewmxU exqtc+JkaLp8bhf/sngPQ1RUXKiwZ5ntIFb1agf2D4oOektTs/ApHVeVnXsDOeYKoSXVXi SM/qSSJJihHLXHT6ngL9a85GwVKNmerGgojVh8HJJYnKr5gDmbz4L1Cp0GDjUM+jDPcTEM 1vX97HCgyFQS3PBeqIXIHsQQ7l+p2bMT9OxzLCUXwaR7C+Nv58Oxtm2QmFlQ X-ME-Proxy: Feedback-ID: i10464835:Fastmail Received: by mail.messagingengine.com (Postfix) with ESMTPA; Thu, 30 Jul 2026 11:50:18 -0400 (EDT) Date: Thu, 30 Jul 2026 16:50:17 +0100 From: Kiryl Shutsemau To: Doug Anderson Cc: Will Deacon , Catalin Marinas , James Morse , Mark Rutland , Marc Zyngier , Petr Mladek , Thomas Gleixner , Andrew Morton , Baoquan He , Puranjay Mohan , Usama Arif , Breno Leitao , Julien Thierry , Lecopzer Chen , Sumit Garg , kernel-team@meta.com, kexec@lists.infradead.org, linux-arm-kernel@lists.infradead.org, linux-kernel@vger.kernel.org Subject: Re: [PATCH v5 0/4] arm64: cross-CPU NMI via SDEI Message-ID: References: MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: X-BeenThere: kexec@lists.infradead.org X-Mailman-Version: 2.1.34 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Sender: "kexec" Errors-To: kexec-bounces+kexec=archiver.kernel.org@lists.infradead.org On Wed, Jul 29, 2026 at 02:37:37PM -0700, Doug Anderson wrote: > Hi, > > On Tue, Jul 28, 2026 at 5:18 AM Kiryl Shutsemau wrote: > > > > The piece that isn't boot-time yet is the hardlockup detector that drives > > all this. perf and buddy are mutually exclusive at compile time. We want > > to use perf watchdog for FEAT_NMI while SDEI needs buddy. > > FWIW: can I ask why? You're worried about the "all CPUs lock up at the > same time" problem? I am aware of some work towards solving that (even > with buddy) by letting the hardware watchdog driver's "bark" interrupt > run at NMI-level (or pseudo-NMI-level). With that change, I'm not > aware of any benefits of the "perf" detector over the buddy one. Honestly, no strong reason. I flagged perf mostly as "the detector you'd reach for once NMIs are back", not from a concrete need. The all-CPUs-wedge-at-once case is the only gap I was vaguely worried about, since there's no live buddy left to notice it. If the NMI-level bark work you mention closes that for buddy, then I don't see a reason to want perf at all -- and as you say, buddy is cheaper. Buddy everywhere would be strictly better for us. -- Kiryl Shutsemau / Kirill A. Shutemov