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 AF30541379F for ; Sun, 27 Sep 2026 17:26:33 +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=1790529994; cv=none; b=AiGgS8eE8htgxG4zw7JT0NEyOrPXVnKVuAt95fl8WZWC3n84hkaV5LkLCdNz81ymeQ40ApUjEKeceMyltHRssRPtVMDj1OCDGxnH1hJdHQNcE2T6a6d+xXw6LCs7hoXUV5cJvfwUdFRb+KT9Rjr/h9yo96iD2Zz8pfpuZOmE29M= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1790529994; c=relaxed/simple; bh=u7TkxzW3x4juS+OVk4UuUwfeHl9Utob1vgraqXPTrB0=; h=Date:From:To:Cc:Subject:Message-ID:References:MIME-Version: Content-Type:Content-Disposition:In-Reply-To; b=U5CR2RJeSu2bmD9GfRoOnPN7dkwbUBJk77fYajLKfge+Gf9TuVkK9PtmBKUPaEprVmJu5AnjjXdI94QfXT3VM5ZxluCQw7R6NxhYPIx7OLVOxDkLi4BzyHcajKqaqgQ4/t4QTBQfSO0Ylj5oxhf2ZQshnpHiL2ZcTaTv7rUyaYk= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=MqW9Sd1M; 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="MqW9Sd1M" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 1DE151F00898; Sun, 27 Sep 2026 17:26:33 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=kernel.org; s=k20260515; t=1790529993; bh=TuuaDpekgfgDG1xsd5kQIZDXGrc07KFH/CrVSLpmawc=; h=Date:From:To:Cc:Subject:References:In-Reply-To; b=MqW9Sd1Mgc2XcmVUMggmcQ5NkOmifOx9I/UQGPTyVM92+fYAOWHjt473hcfNoY7cj ah73PUmxjrVxszCYl1cGxQcBRTu+NKcQlwVEQX0WuUIixVfZr5EquRmOSsBxnaKzK/ YDgWiQrHlcVCgZnb6bnsK0Si2JqhWJBXCCD9oAhFvGZtruIURWKaFWhabYe+G6YfVx 0uU3VOcsPvbyp/0tIBZDAIoKRLDg9xUbuSZu7u06GgjXwfQh5k1Re4C3KJxTt6AdYs lzw+9+KGvgMbOr9njvowVfn+KnSj1IZc5dnJ3WcVG93IIjOg0iY0M57sf0bhS/flzs NaPpq+y9pPJ6g== Received: from phl-compute-07.internal (phl-compute-07.internal [10.202.2.47]) by mailfauth.phl.internal (Postfix) with ESMTP id 4051DF40066; Sun, 27 Sep 2026 13:26:32 -0400 (EDT) Received: from phl-frontend-04 ([10.202.2.163]) by phl-compute-07.internal (MEProxy); Sun, 27 Sep 2026 13:26:32 -0400 X-ME-Sender: X-ME-Received: X-ME-Proxy-Cause: dmFkZTF2wYukihSOr307lfKZHsXSU41dCS/+c7pM1vG1Ie3zgbM85D04/zRSSOZocH4w95 SYQwC1Aax+ksTT5qFIOeCIAqu2VtGNONzEJXyJvSH6I8HN71yP5sjf/6VHzagOzvqVy1FX nIBFdWVlI+S9SiuxiWGqBnPw5qa4SYX2WZKXuxi7rCkb0ZQ7Mb0ORUyLT6GbaItL+/kDFR NNicQNdX+26Sk2fxcqqAzcEJc0z0uPNE08whGuESuh7HiuZh60M961WaBytJ8uy7om7YZs InOwEhfcW9WgeZKV0ybWZSq7EuY7pYRvN2IBNNMbfbzATO+6YvKqEBqBZTRW7kXpGzmqSr pqmhT5teSJnkmU0xQCFbzWbAxfIX8qFSwD2lgmMZ9h41VsV6ijJW0mcudUaK9glqXtXaFj wole5IL0AdhiCpr3b1pD4mrG+0Jfhui6aOS5Tom9O8CzNEi76puj0aZe5QDwv2pOBAO5h4 /DRhg2/W4zvMXxIZijAotf/tZZr6k/iIUSXthAy5f+pTvtyB6X22mz9JG0HclYSPl2ObKC n2CpyrHTvwowyQBSwq+635tni+mFzZMg4gJKJMjJzE+VUFXfA1d1zehTqujuWZwF5dvqPB mlub6jZJG64V0F237ooidcHiKjBES8emAEmbomLzp7Q94uUfGWsXH21yaydw X-ME-Proxy: Feedback-ID: i8dbe485b:Fastmail Received: by mail.messagingengine.com (Postfix) with ESMTPA; Sun, 27 Sep 2026 13:26:31 -0400 (EDT) Date: Sun, 27 Sep 2026 19:26:30 +0200 From: Boqun Feng To: Mathieu Desnoyers Cc: "Paul E . McKenney" , linux-kernel@vger.kernel.org, Bradley Morgan , Gary Guo , rcu@vger.kernel.org, lkmm@lists.linux.dev Subject: Re: [PATCH hazptr 4/4] hazptr: Introduce "try acquire" fast path, fallback to overflow list Message-ID: References: <20260927155134.4740-1-mathieu.desnoyers@efficios.com> <20260927155134.4740-5-mathieu.desnoyers@efficios.com> <5c78c338-1be6-456b-b963-bcfc62748aab@efficios.com> 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=us-ascii Content-Disposition: inline In-Reply-To: <5c78c338-1be6-456b-b963-bcfc62748aab@efficios.com> On Sun, Sep 27, 2026 at 01:15:39PM -0400, Mathieu Desnoyers wrote: [...] > > > With this change, the scan on per-CPU slots don't need to expect a > > > wildcard anymore, because none can be produced by readers. Wildcards are > > > only expected within overflow lists. > > > > > > > Ok, I was missing something, but I think it's better to call it out. > > Wildcards can only exist in the overflow lists when the context is not > > preemptible. In other words, there won't be a preempted readers blocking > > the synchronize_hazptr() with a wilcard in the overflow list. > > Exactly ! Wildcard slots only exist during the short time-frame of the > preempt-off read-side code region (few instructions). And with this > patch, this does not even happen very often, because the fast path don't > rely on the wildcards. > > > > > So no more design trade-off question from me :) > > > > Are you sure ? Scrolling down.... > I do feel with scan thread support and call_hazptr() support, we will need to tweak the design and implementation some more, but right now it does look good to me :) Regards, Boqun [...]