From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from foss.arm.com (foss.arm.com [217.140.110.172]) by smtp.subspace.kernel.org (Postfix) with ESMTP id AF0615372F3 for ; Wed, 23 Sep 2026 16:14:21 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=217.140.110.172 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1790180064; cv=none; b=Vm14bfwDmNKnCdFrcDSXzt95XQZCKRrT45IKsknHTzbrBuSNbJGJ93PMLjD7fEDQ9kdq/ZxYXf50iJtSQlBYVsjFkY0aJu0NlRlIs/kxmWBTjgjPjV4OgEDxhpJ96KuypTUYI1tymwYbywGXz6c7uIZdZGhH7XW89H1jxuQTaIA= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1790180064; c=relaxed/simple; bh=9EBIGd9e2m8HBAqkNbb+EjJdoUI8yMILNRtqw6GVPOM=; h=Date:From:To:Cc:Subject:Message-ID:References:MIME-Version: Content-Type:Content-Disposition:In-Reply-To; b=QNjMvgveh0RJIdYUStO1okw0GovvvFLukrenx32aDkR5PR5jdXy/cxBmAI5Hb7gg+YMp2Mqd0LZLaXKyLmHKuOpC3iD3yWhjwWLxXgHUgbYnLcVoQ0Z6GOxTMybPEzsNmLwn4V0qZK3YXILIlz/pi+P4fVG1kxNqpFrBopQWA6o= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=arm.com; spf=pass smtp.mailfrom=arm.com; dkim=pass (1024-bit key) header.d=arm.com header.i=@arm.com header.b=feFCPkW3; arc=none smtp.client-ip=217.140.110.172 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=arm.com Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=arm.com Authentication-Results: smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=arm.com header.i=@arm.com header.b="feFCPkW3" 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 ECBAE1570; Wed, 23 Sep 2026 09:14:16 -0700 (PDT) Received: from arm.com (usa-sjc-mx-foss1.foss.arm.com [172.31.20.19]) by usa-sjc-imap-foss1.foss.arm.com (Postfix) with ESMTPSA id C5E003F86C; Wed, 23 Sep 2026 09:14:18 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=simple/simple; d=arm.com; s=foss; t=1790180060; bh=9EBIGd9e2m8HBAqkNbb+EjJdoUI8yMILNRtqw6GVPOM=; h=Date:From:To:Cc:Subject:References:In-Reply-To:From; b=feFCPkW3shidAGRi0gtGaIPg3jJgWeecq0pXz59fMYfi8toH2Aqe7aKu0CfWK44oP rdyQJRrd761lAhO9YIBPaZxDGNYUb43W0pIcLL53BP5YZz8ZiFXjk9lM6W/bw5dIXS U20QZqzwHUbjqAFoAi6n3VA4EwUl+Nb3TJo3eSs0= Date: Wed, 23 Sep 2026 17:14:15 +0100 From: Catalin Marinas To: Leonardo Bras Cc: Linus Walleij , Will Deacon , Marc Zyngier , Oliver Upton , Joey Gouly , Suzuki K Poulose , Zenghui Yu , linux-arm-kernel@lists.infradead.org, kvmarm@lists.linux.dev, Usama Anjum Subject: Re: [PATCH v2] arm64: clear_page[s] using memset Message-ID: References: <20260916-aarch64-clear-pages-c-v2-1-0393769f7912@kernel.org> Precedence: bulk X-Mailing-List: kvmarm@lists.linux.dev List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: On Wed, Sep 16, 2026 at 04:54:09PM +0100, Leonardo Bras wrote: > On Wed, Sep 16, 2026 at 04:28:51PM +0100, Leonardo Bras wrote: > > On Wed, Sep 16, 2026 at 12:03:56PM +0200, Linus Walleij wrote: > > > There is no need to try to second-guess the compiler when > > > clearing memory. Just call memset() like everyone else. > > > > > > Since memset() already has an architecture-local MOPS > > > optimization, we do not need to do anything else to preserve > > > the MOPS optimization. > > > > > > While at it, implement the shorthand for directly calling > > > the new prototype clear_pages() for larger page chunks. > > > > > > No performance regressions can be seen, the fastpath > > > benchmarks differences are in the noise. > > > > > > Usama Anjum tested next-20260821 with one warm-up and three repeats > > > in four sessions, for a total of 12 measured runs. The commands were: > > > > > > perf bench mem memset -k 1GB -f default -s 16GB > > > perf bench mem mmap -p 1GB -f demand -s 32GB -l 5 > > > perf bench mem mmap -p 4KB -f demand -s 32GB -l 5 > > > > > > The results were: > > > > > > aws-m7g.metal: > > > Benchmark Base bytes/sec Change with patch > > > memset 1GB 63932542232.12 1.92% > > > mmap 1GB 63272579168.03 -0.57% > > > mmap 4KB 49692830849.48 -1.11% > > > > > > cesw-aarch64-ampereone-1s-a192-32x: > > > Benchmark Base bytes/sec Change with patch > > > memset 1GB 33895562998.71 0.25% > > > mmap 1GB 34338454210.17 1.16% > > > mmap 4KB 25687107580.90 -0.85% [...] > > Looking on that, I see that the memset() implementation uses setp, setm, > > sete, while the clear_page()'s uses setpn, setmn, setn for the case with > > MOPS. But then, reading into the docs, the instructions seem pretty much > > the same thing. [...] > Oh, I browsed a bit here, and IIUC none of the tested machines have > FEAT_MOPS, is that right? > > If that's the case, the tests are exactly to what is different between > patched and current versions. There should be no impact on MOPS version as > the instructions are basically the same. Logically, yes, they are the same. From a performance perspective, there may be a difference between the temporal and non-temporal variants, depending on the usage. I think it would be good to run the benchmarks with the current implementation without DC ZVA. I don't think we have an easy way to do this on the command line, so we can simply hard-code the DZP=1 check and fall back to the STP or STNP in both cases. Otherwise I'm fine with the patch as well, good clean-up. -- Catalin