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 961D3384223 for ; Thu, 30 Jul 2026 15:50:20 +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=1785426621; cv=none; b=oQIjx/tA2l5QAOvdWWXabL9bP7xOlYWFD92dh+0c290X25v3u3yr3ELQ+FEdrzCuvfbssty1BQQt4/4VGXe4xvBwY4mQwV5YveNAq9R2Yq5mUB8gDcpz7Uu30a/mgChU6hHBEDxzKyuYQUgjEZY/xoaM2BYJlgLDM3a13wX/MbI= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1785426621; c=relaxed/simple; bh=4YO3GVwV7H3tmNddzf1ZEalpyD2BXyJ0sd1XSsOJ8Bc=; h=Date:From:To:Cc:Subject:Message-ID:References:MIME-Version: Content-Type:Content-Disposition:In-Reply-To; b=BmcliUtYN+4+XquvsgRd/I7l9TmC02dXjrfYBCypjLiLUHiapQZub2dTRH6Oo3qAcfSHJF+6VBI5/f1AVCsn6zRWxNuOWclsTcaDfX2JboKh+/qer5I+SZXnsRXElkDQz0XFSEOJN+L6oQm3WwvqU78oCZBZWh9S425P/kEbmOA= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=du3CuQn5; 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="du3CuQn5" Received: by smtp.kernel.org (Postfix) with ESMTPSA id F26371F00A3E; 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: 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, 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