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 56DE1C55184 for ; Tue, 4 Aug 2026 16:47:43 +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:Content-Transfer-Encoding: Content-Type:In-Reply-To:From:References:Cc:To:Subject:MIME-Version:Date: Message-ID:Reply-To:Content-ID:Content-Description:Resent-Date:Resent-From: Resent-Sender:Resent-To:Resent-Cc:Resent-Message-ID:List-Owner; bh=/m4yAZ5mIsOFZEiU4veHFKr2AoqsHnJrC8u0FSLN/U8=; b=ENOoJNEiVpDZrz12WTZkvbVfkE NFBo/0Rw6vNDaa8z3F7Gjw54Mzxe4N+ueqh1g6llShGlkFSL4pwQmrBWO1d+cx3GanKhyQ9losR9d VgKz9d1kIVmBhqwExbeqyBFFYVFdUGbWIp3SpOgRE4/CfGmaVIDVkycgYn+uesxPMLpk3aLJr8k8Y rb1s9HGgJcI09u0GrcrZ0O2+0Lh6TrqIZJvSDYS/cHe7ETJ1QNWwZQ660uqLG7UD5ZYEa+FtNZ7RC /ZSSgRmPGmLB9eZLVetL/i3EmQvg8z+aKi00xAqjLCP4qmYdCh+lOv2vSLP9pdykXFggBIJlG6iWt v4tGkbTQ==; Received: from localhost ([::1] helo=bombadil.infradead.org) by bombadil.infradead.org with esmtp (Exim 4.99.1 #2 (Red Hat Linux)) id 1wrIIi-00000002Nwp-3KKI; Tue, 04 Aug 2026 16:47:36 +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 1wrIIh-00000002Nwh-16Yx for linux-arm-kernel@lists.infradead.org; Tue, 04 Aug 2026 16:47:35 +0000 Received: from smtp.kernel.org (quasi.space.kernel.org [100.103.45.18]) by sea.source.kernel.org (Postfix) with ESMTP id E004643D11; Tue, 4 Aug 2026 16:47:34 +0000 (UTC) Received: by smtp.kernel.org (Postfix) with ESMTPSA id 4C8661F000E9; Tue, 4 Aug 2026 16:47:29 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=kernel.org; s=k20260515; t=1785862054; bh=/m4yAZ5mIsOFZEiU4veHFKr2AoqsHnJrC8u0FSLN/U8=; h=Date:Subject:To:Cc:References:From:In-Reply-To; b=KAAuqSzDp0wplUBF9Fq0YxQTEF733hGX4xj4Y90DI8bZ9hL6VeW908wQGHnfPdsZu rrCzEKEjeah6szU+pl4/gkNRp/qVwmNa+ywme1I4lHz2SuIjJP5BWpFfGVgNYA9Eo4 v9vjxuwD+2Hyaigth9wcOM+k8DBaj/CIgX7XW4LMIS9cw03FKnhczraAQ7g2I/cQrE bbnOGQeUiAJAqPJElj7deWCtVPBmTP81tXGPOIZaY1hjfVOreivQ/k5PuK/I13vFzF CRX3ouvSBJ635W/6cspzFiRlHWV0BzyJiBOZs8jir0u29LyxpLKQHNzprXKiaDAND6 Np0mwa4lS6oug== Message-ID: <84b31836-1d10-4bec-a469-468b91fd4645@kernel.org> Date: Tue, 4 Aug 2026 18:47:26 +0200 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [RFC v2 PATCH 0/16] Optimize this_cpu_*() ops for non-x86 (ARM64 for this series) To: "Christoph Lameter (Ampere)" , "Lorenzo Stoakes (ARM)" Cc: Mark Rutland , Yang Shi , Ryan Roberts , dennis@kernel.org, tj@kernel.org, urezki@gmail.com, catalin.marinas@arm.com, will@kernel.org, akpm@linux-foundation.org, hca@linux.ibm.com, gor@linux.ibm.com, agordeev@linux.ibm.com, linux-mm@kvack.org, linux-arm-kernel@lists.infradead.org, linux-kernel@vger.kernel.org, Linus Torvalds , Jason Gunthorpe References: <20260715180455.515692-1-yang@os.amperecomputing.com> <0344c559-1959-4531-9265-d5a5180eb7cd@arm.com> <25d1e09b-53e4-7cd5-87db-b58437e4e690@gentwo.org> <4887267b-dc26-4c33-96ca-8dff054a0d1f@kernel.org> <63ea8156-a109-b2a2-6d35-1c17ad7f1a9d@gentwo.org> From: "David Hildenbrand (Arm)" Content-Language: en-US Autocrypt: addr=david@kernel.org; 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charset=UTF-8 Content-Transfer-Encoding: 7bit X-BeenThere: linux-arm-kernel@lists.infradead.org X-Mailman-Version: 2.1.34 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Sender: "linux-arm-kernel" Errors-To: linux-arm-kernel-bounces+linux-arm-kernel=archiver.kernel.org@lists.infradead.org On 8/4/26 18:19, Christoph Lameter (Ampere) wrote: > On Tue, 4 Aug 2026, Lorenzo Stoakes (ARM) wrote: > >> Since this work seems to be very much arm64-focused, perhaps it's therefore >> worth looking at an alterative solution that's specific to the arch, like the >> one suggested by Mark ([1])? >> >> [0]:https://lore.kernel.org/all/CAHk-=wire3dzhHx=KiL_f5Rj0=1u9ustsa33QoR-F9-v-NU9Ng@mail.gmail.com/ >> [1]:https://lore.kernel.org/linux-arm-kernel/al_DpFJFcmVhxpvW@J2N7QTR9R3/ > > Mark's solution does replace the preempt_enable/disable sections with a > rather hacky restart logic. It relies on a long preemable and postscript > to each per cpu operations. Okay, so 3 simple instructions of preemable is "long preemable"? In which universe? But I am sure you did you homework and have data to back up your claims. Please share that data, because I am very curious. > > It does not remove the code entirely like the proposed patchset here and > cannot produce the same compact code as x86. Mark's solution is the obvious improvement to the problem, doing it just like s390 already does. If the proposed solution has a significant benefit over Mark's solution it could be discussed as a next step; and it must be backed with sufficient data to warrant all this complexity here. -- Cheers, David