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 73DB1CA1007 for ; Tue, 2 Sep 2025 21:44:46 +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=++0HR791FkLxlUHcefszxk8YdT4/39Fh4fcB7XpqyVw=; b=YfnxH52McrAuf9FIQ57IFqjrLl KmYvXEA3nNFnuVkxguMob/MZp7cDge5MvF/21HhqjDvczgvkQCUmZS7Z6ZVGiFFQv7nMNbaRWnEpg fWafLrWVTVhbZ3i9cYufJBZLpICRoXrjMpGA79acPglHuMQWyncakTFUGjFHYcFsmy4A9dL1nEfre /QkaK16P6uRAyJ3aRKJa9WVCEqsZ4bp5lHF82A3Ic2B9hj6Q4Fq5RTgk+JiFX53rz4EQJEXpRJ/Np UeN9poezlVdpOV8PNGNq6tfhHc03KCngxrsQJ9wRW0WWmvvPgt/MxoRqCs4v9vXL0EfwGSxf/0kwm 49CBrnqw==; Received: from localhost ([::1] helo=bombadil.infradead.org) by bombadil.infradead.org with esmtp (Exim 4.98.2 #2 (Red Hat Linux)) id 1utYnw-00000002D2G-0iIN; Tue, 02 Sep 2025 21:44:40 +0000 Received: from foss.arm.com ([217.140.110.172]) by bombadil.infradead.org with esmtp (Exim 4.98.2 #2 (Red Hat Linux)) id 1utUJ7-000000014BY-2caQ for linux-arm-kernel@lists.infradead.org; Tue, 02 Sep 2025 16:56:35 +0000 Received: from usa-sjc-imap-foss1.foss.arm.com (unknown [10.121.207.14]) by usa-sjc-mx-foss1.foss.arm.com (Postfix) with ESMTP id 1EFE326BE; Tue, 2 Sep 2025 09:56:23 -0700 (PDT) Received: from [10.1.36.209] (unknown [10.1.36.209]) by usa-sjc-imap-foss1.foss.arm.com (Postfix) with ESMTPSA id 893283F694; Tue, 2 Sep 2025 09:56:30 -0700 (PDT) Message-ID: <06ca976e-03ff-4376-a29d-24993282dda0@arm.com> Date: Tue, 2 Sep 2025 17:56:29 +0100 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [RFC PATCH v1 0/2] Don't broadcast TLBI if mm was only active on local CPU Content-Language: en-GB To: Catalin Marinas Cc: Will Deacon , Mark Rutland , James Morse , linux-arm-kernel@lists.infradead.org, linux-kernel@vger.kernel.org References: <20250829153510.2401161-1-ryan.roberts@arm.com> From: Ryan Roberts In-Reply-To: Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit X-CRM114-Version: 20100106-BlameMichelson ( TRE 0.8.0 (BSD) ) MR-646709E3 X-CRM114-CacheID: sfid-20250902_095633_746404_61343B3D X-CRM114-Status: GOOD ( 20.11 ) 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 02/09/2025 17:47, Catalin Marinas wrote: > On Fri, Aug 29, 2025 at 04:35:06PM +0100, Ryan Roberts wrote: >> Beyond that, the next question is; does it actually improve performance? >> stress-ng's --tlb-shootdown stressor suggests yes; as concurrency increases, we >> do a much better job of sustaining the overall number of "tlb shootdowns per >> second" after the change: >> >> +------------+--------------------------+--------------------------+--------------------------+ >> | | Baseline (v6.15) | tlbi local | Improvement | >> +------------+-------------+------------+-------------+------------+-------------+------------+ >> | nr_threads | ops/sec | ops/sec | ops/sec | ops/sec | ops/sec | ops/sec | >> | | (real time) | (cpu time) | (real time) | (cpu time) | (real time) | (cpu time) | >> +------------+-------------+------------+-------------+------------+-------------+------------+ >> | 1 | 9109 | 2573 | 8903 | 3653 | -2% | 42% | >> | 4 | 8115 | 1299 | 9892 | 1059 | 22% | -18% | >> | 8 | 5119 | 477 | 11854 | 1265 | 132% | 165% | >> | 16 | 4796 | 286 | 14176 | 821 | 196% | 187% | >> | 32 | 1593 | 38 | 15328 | 474 | 862% | 1147% | >> | 64 | 1486 | 19 | 8096 | 131 | 445% | 589% | >> | 128 | 1315 | 16 | 8257 | 145 | 528% | 806% | >> +------------+-------------+------------+-------------+------------+-------------+------------+ >> >> But looking at real-world benchmarks, I haven't yet found anything where it >> makes a huge difference; When compiling the kernel, it reduces kernel time by >> ~2.2%, but overall wall time remains the same. I'd be interested in any >> suggestions for workloads where this might prove valuable. > > I suspect it's highly dependent on hardware and how it handles the DVM > messages. There were some old proposals from Fujitsu: > > https://lore.kernel.org/linux-arm-kernel/20190617143255.10462-1-indou.takao@jp.fujitsu.com/ > > Christoph Lameter (Ampere) also followed with some refactoring in this > area to allow a boot-configurable way to do TLBI via IS ops or IPI: > > https://lore.kernel.org/linux-arm-kernel/20231207035703.158053467@gentwo.org/ > > (for some reason, the patches did not make it to the list, I have them > in my inbox if you are interested) > > I don't remember any real-world workload, more like hand-crafted > mprotect() loops. > > Anyway, I think the approach in your series doesn't have downsides, it's > fairly clean and addresses some low-hanging fruits. For multi-threaded > workloads where a flush_tlb_mm() is cheaper than a series of per-page > TLBIs, I think we can wait for that hardware to be phased out. The TLBI > range operations should significantly reduce the DVM messages between > CPUs. I'll gather some more numbers and try to make a case for merging it then. I don't really want to add complexity if there is no clear value. Thanks for the review. Thanks, Ryan