From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from smtp.kernel.org (aws-us-west-2-korg-mail-1.web.codeaurora.org [10.30.226.201]) (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 CA5762BDC04 for ; Fri, 6 Feb 2026 16:16:42 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=10.30.226.201 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1770394602; cv=none; b=rHXkwFYjPdO+QodelBQiwa9YyorbpXcMDC7fRg3AQAd3YWbwyJ2OMC+0Udd2VKX+2KYsX+Y7UKvzLcpmG/HKfGA+kehoOJP52dJ7M5Cs+4mf8LVFcCKscH6JirrTuqZiGmPWwnKIYae49N1FYWC+1dcbDHkttKJx0lENpsSYKiA= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1770394602; c=relaxed/simple; bh=mkEIRgVxKtBAjSFWvWQi1uEr1i+PMSOlpgfVn+mnrRc=; h=Date:From:To:Cc:Subject:Message-ID:References:MIME-Version: Content-Type:Content-Disposition:In-Reply-To; b=YvpuuO/RbEXGn7EsbmzIQrowf9z8zdKhfDGY0w/xLBjsCIa4gPjmN0AAWPJhHr4HVqkYpDVNYzPN1yN+bxelQwsvy5pNhVVnjz6TCz4tpDn0tnD+H6cwe4UmRgvwuzJaMbB0q/17NXBPOGssZ4w5Xlg3lq+f4knaoBWSHdUN9cc= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=eMiMZYTO; arc=none smtp.client-ip=10.30.226.201 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b="eMiMZYTO" Received: by smtp.kernel.org (Postfix) with ESMTPSA id DDE4FC2BC86; Fri, 6 Feb 2026 16:16:41 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1770394602; bh=mkEIRgVxKtBAjSFWvWQi1uEr1i+PMSOlpgfVn+mnrRc=; h=Date:From:To:Cc:Subject:References:In-Reply-To:From; b=eMiMZYTOoNaRoWwdFE5mLYf60vJb7YbBIxOuc4u26MQkBHtaFoNqnhPQNkHQ4LqOa wqJOLNbCJUCKsl7BQ6kSiO9okj19nE+vFTv0/W2bKzqvEsicExuHCFlJ1rglRrWSZj mIhP7wwmkCgJEpxFrUxPCAX+U16aCm2k1qpGmX2w9cwfVBII7+MaM74pCJ5eyCXy0Z LMvaB3KW68oHaPpRuYkv9PahfQdlNXX2ZHZ8127Gp9tGT25EF1+gC+89GaiTlLuaI8 YrTWLhkzinzJ0TDZfERNbmPR3moqT6a4g91EW/2UeX+M9ZxIQTg0BdQvHWjcIxb6Wc Yg4qirsA72sWQ== Received: from phl-compute-01.internal (phl-compute-01.internal [10.202.2.41]) by mailfauth.phl.internal (Postfix) with ESMTP id D6742F4006B; Fri, 6 Feb 2026 11:16:40 -0500 (EST) Received: from phl-frontend-04 ([10.202.2.163]) by phl-compute-01.internal (MEProxy); Fri, 06 Feb 2026 11:16:40 -0500 X-ME-Sender: X-ME-Received: X-ME-Proxy-Cause: gggruggvucftvghtrhhoucdtuddrgeefgedrtddtgddukeekiedvucetufdoteggodetrf dotffvucfrrhhofhhilhgvmecuhfgrshhtofgrihhlpdfurfetoffkrfgpnffqhgenuceu rghilhhouhhtmecufedttdenucesvcftvggtihhpihgvnhhtshculddquddttddmnecujf gurhepfffhvfevuffkfhggtggujgesthdtredttddtvdenucfhrhhomhepuehoqhhunhcu hfgvnhhguceosghoqhhunheskhgvrhhnvghlrdhorhhgqeenucggtffrrghtthgvrhhnpe elueehtefhtddtgfejvdejueehhfekteevueeuueekgeetieeggeehvdffhefhhfenucff ohhmrghinhepkhgvrhhnvghlrdhorhhgnecuvehluhhsthgvrhfuihiivgeptdenucfrrg hrrghmpehmrghilhhfrhhomhepsghoqhhunhdomhgvshhmthhprghuthhhphgvrhhsohhn rghlihhthidqudeijedtleekgeejuddqudejjeekheehhedvqdgsohhquhhnpeepkhgvrh hnvghlrdhorhhgsehfihigmhgvrdhnrghmvgdpnhgspghrtghpthhtohepvddvpdhmohgu vgepshhmthhpohhuthdprhgtphhtthhopehjohgvlhgrghhnvghlfhesnhhvihguihgrrd gtohhmpdhrtghpthhtohepphgvthgvrhiisehinhhfrhgruggvrggurdhorhhgpdhrtghp thhtoheplhihuhguvgesrhgvughhrghtrdgtohhmpdhrtghpthhtoheprhhushhtqdhfoh hrqdhlihhnuhigsehvghgvrhdrkhgvrhhnvghlrdhorhhgpdhrtghpthhtoheplhhinhhu gidqkhgvrhhnvghlsehvghgvrhdrkhgvrhhnvghlrdhorhhgpdhrtghpthhtohepthhglh igsehlihhnuhhtrhhonhhigidruggvpdhrtghpthhtohepsghoqhhunhdrfhgvnhhgsehg mhgrihhlrdgtohhmpdhrtghpthhtohepuggrnhhivghlrdgrlhhmvghiuggrsegtohhllh grsghorhgrrdgtohhmpdhrtghpthhtohepohhjvggurgeskhgvrhhnvghlrdhorhhg X-ME-Proxy: Feedback-ID: i8dbe485b:Fastmail Received: by mail.messagingengine.com (Postfix) with ESMTPA; Fri, 6 Feb 2026 11:16:40 -0500 (EST) Date: Fri, 6 Feb 2026 08:16:39 -0800 From: Boqun Feng To: Joel Fernandes Cc: Peter Zijlstra , Lyude Paul , rust-for-linux@vger.kernel.org, linux-kernel@vger.kernel.org, Thomas Gleixner , Boqun Feng , Daniel Almeida , Miguel Ojeda , Alex Gaynor , Gary Guo , =?iso-8859-1?Q?Bj=F6rn?= Roy Baron , Benno Lossin , Andreas Hindborg , Alice Ryhl , Trevor Gross , Danilo Krummrich , Andrew Morton , Ingo Molnar , Will Deacon , Waiman Long Subject: Re: [PATCH v17 02/16] preempt: Track NMI nesting to separate per-CPU counter Message-ID: References: <6792E792-2043-4BF5-952B-90847703F23F@nvidia.com> Precedence: bulk X-Mailing-List: rust-for-linux@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: On Fri, Feb 06, 2026 at 11:00:16AM -0500, Joel Fernandes wrote: > > > On 2/6/2026 10:28 AM, Boqun Feng wrote: > >> I was also coming from the goal of long term kernel code maintainability. If > >> we decide to have additional preempt count flags in the future, does special > >> casing 32 bit add even more complexity? (not rhetorical, really asking) > >> > > First, given what preempt count is, I don't think that'll happen > > frequently. > > Not sure I buy the argument of not happening frequently. I don't think any of us > have a crystal ball. There are cases in the future that can come up IMO. > It's just being realistic, and we pretty much use all the bits there. > > Also I think the reality is that we care about 64bit> performance more than > 32bit, in that sense, if this "conditional 32 bit > > preempt count case" becomes an issue, the reasonable action to me is > > just making all preempt count 64bit > > You might be missing something here. You can't make all of preempt count 64 bit, > that's the point, it doesn't work. That's why Peter did what he did to > special-case 32 bit. See: > https://lore.kernel.org/all/20251020204421.GA197647@joelbox2/ > > That said, I am ok with the approach now that Peter mentions 32-bit x86 is > "deprecated". :-) > Yeah, "can't" is a strong word? ;-) I did say if we care more about performance on 64bit than 32bit and can afford slowing down 32bit preemption disabling in the case where "we decide to have additional preempt count flags", THEN we can make all preempt count 64bit. Regards, Boqun > -- > Joel Fernandes >