From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from mail.mainlining.org (mail.mainlining.org [5.75.144.95]) (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 145073546D7; Sat, 19 Sep 2026 23:59:21 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=5.75.144.95 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1789862364; cv=none; b=IEHZVYcGz/ElC48o0VPhTvBKzzooClWAdISsB+WFFdvB+wsx6TPoEKLxqaae5CadPskIFq+TQdrDCWNiGXwBohUcumJio08bv55X/2lEmp7zkIaBXkCWTXkAotIwrPj6vxcWM/YEWaM/6cbH/gb6ggNVzNCR473pySKniuYsKkY= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1789862364; c=relaxed/simple; bh=rAhVNDiL11CVY48zH2oCKIRAYv0Q6pkIWHnxHVKp9Lg=; h=Date:From:To:CC:Subject:In-Reply-To:References:Message-ID: MIME-Version:Content-Type; b=OI8mGIasCmoBEG5wY0/Xi4agJgkd+L5MJAf6N5bOy6kxIDBoHweMIzTEx4OKn2OaQfkr25115t0yl30Bwg4jbvLPXCayB78P7zBfmxUJ/ccJn/lfdDlaN7wRZY7QDdzjscINsE2UImZdh9mlhjlP2mS2WyAWu8Z+mYrFCdvG9o0= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=pass (p=reject dis=none) header.from=mainlining.org; spf=pass smtp.mailfrom=mainlining.org; dkim=pass (2048-bit key) header.d=mainlining.org header.i=@mainlining.org header.b=r8xwZZWf; dkim=permerror (0-bit key) header.d=mainlining.org header.i=@mainlining.org header.b=9RyAbuNy; arc=none smtp.client-ip=5.75.144.95 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=reject dis=none) header.from=mainlining.org Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=mainlining.org Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=mainlining.org header.i=@mainlining.org header.b="r8xwZZWf"; dkim=permerror (0-bit key) header.d=mainlining.org header.i=@mainlining.org header.b="9RyAbuNy" DKIM-Signature: v=1; a=rsa-sha256; s=202507r; d=mainlining.org; c=relaxed/relaxed; h=Message-ID:Subject:To:From:Date; t=1789862290; bh=pY6k578HAOH4JwKTJoaKCmp Jhb02KWQm0IuRCXWcjGI=; b=r8xwZZWfswZEzq1GcsmKlLofGD/op0oLwpha/c4V6+lKMYBgcz 4q1m3icfYOa1yeeMOgHFBRnU0vmnkLdkOVVj5Lj31EV3yuvvSVoHFe6GtF2JGoG26Q1QPoNltXO Tqp7P0vWiUgx4GqCiFjhwt+KSplMLGHZdjJvb5O7K3F4XPVvjkLmW5bQjWxRYmvmwNIMalFfqVY 8n7bPpmeN/pg9c/OtcLEF1GCBAR885Zdifk4TmrGW+QqbzQlkwx2hUxAjJR8gEWWsUjKz5qPgzr 466Ss12BpkY18bFns6Ywbj738BJBx0+vEitSKezaiO66ZrNuha2/GRfTgAM5/XRf0BA==; DKIM-Signature: v=1; a=ed25519-sha256; s=202507e; d=mainlining.org; c=relaxed/relaxed; h=Message-ID:Subject:To:From:Date; t=1789862290; bh=pY6k578HAOH4JwKTJoaKCmp Jhb02KWQm0IuRCXWcjGI=; b=9RyAbuNyB3FsFzP95+hiYvrWbusSXlA8maMnSi3RU0Z10tbDlF L1TbfAjP1xllfOdKbkEdfYW+gxnhnK9AiRAg==; Date: Sun, 20 Sep 2026 00:58:10 +0100 From: Bradley Morgan To: Linus Torvalds CC: "Paul E. McKenney" , rcu@vger.kernel.org, linux-kernel@vger.kernel.org, kernel-team@meta.com, Mathieu Desnoyers , Boqun Feng , Steven Rostedt , lkmm@lists.linux.dev, Zqiang , Wang Lian , Kunwu Chan , Nicholas Piggin , Michael Ellerman , Greg Kroah-Hartman , Sebastian Andrzej Siewior , Will Deacon , Peter Zijlstra , Alan Stern , John Stultz , Andrew Morton , Frederic Weisbecker , Joel Fernandes , Josh Triplett , Uladzislau Rezki , Lai Jiangshan , Zqiang , Ingo Molnar , Waiman Long , Mark Rutland , Thomas Gleixner , Vlastimil Babka , maged.michael@gmail.com, Mateusz Guzik , Jonas Oberhauser , linux-mm@kvack.org Subject: Re: [PATCH 01/28] hazptr: Implement Hazard Pointers In-Reply-To: References: <20260919000056.3132131-1-paulmck@kernel.org> <6B1FC39D-6EB0-433A-8E49-E5EFC9379AD7@mainlining.org> Message-ID: <4C1A2E71-BC0E-4512-9991-7974BF17069D@mainlining.org> 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-Transfer-Encoding: 8bit On 19 September 2026 18:00:06 BST, Linus Torvalds wrote: >On Sat, 19 Sept 2026 at 09:35, Bradley Morgan >wrote: >> >> I think hazard pointers are good, what test do YOU suggest we do here? > Whew! Talking to my idol, best day ever. >I want to see a single real-world example of "look, this speeds this >real load up by 10%, and the kernel code was actually cleaned up in >the process because hazard pointers are great". well they are, but the big maintainer blokes would want to test and stuff. I'm just a measly reviewer. > >Not a microbenchmark that tests just the hazard pointers themselves, >but a real kernel feature that has been converted to hazard pointers, >and in the process actually shows improvement. > >The ONLY reason for hazard pointers to ever be merged is if they >actually buy us something real. > >So I want to see that 'real" thing. > >I want to see how easy/hard it is to actually convert a real current >user, and I want to see how it actually results in measurable >improvements in performance. > >Something *core*. Something that everybody uses. Because I'm not in >the least interested in a new subtle feature that interacts with the >scheduler and is only used for some random driver or (to pick the only >example I have ever seen) AppArmor. > >Now, obviously, the thing that would impress me is something like the >dcache. If *that* can be converted, and it shows real improvements on >some real benchmark, then I'm sold. > >Now, I don't really expect that kind of major test-case, but I do >expect *something* meaningful. Not a driver. Not a test module. Real >code. > >IOW: "Show me the money". > >Because the kernel is *not* some kind of acadmic project. Never has been. > >I simply don't want to merge something that is touted as an >alterantive to RCU - which we obviously depend on very very heavily - >without something *major* that actually uses it and shows the >real-world advantages. > >The discussion about hazard pointers in the kernel has been around for >a few years by now. If there isn't some real core feature that was >converted to show that, then I think that's already a failure >indication. > >I'm hoping that those patches and numbers already exist, and I just >haven't seen them. I hope this ends up being merged. > > Linus > --- Thanks! "I'm not a very positive person" - Linus torvalds