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 X-Spam-Level: X-Spam-Status: No, score=-3.9 required=3.0 tests=BAYES_00,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI, SPF_HELO_NONE,SPF_PASS autolearn=no autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 350FEC433DF for ; Wed, 14 Oct 2020 19:56:26 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 649AB2222C for ; Wed, 14 Oct 2020 19:56:25 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (1024-bit key) header.d=alien8.de header.i=@alien8.de header.b="rQa3QO0O" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1728528AbgJNT4Y (ORCPT ); Wed, 14 Oct 2020 15:56:24 -0400 Received: from mail.skyhub.de ([5.9.137.197]:57154 "EHLO mail.skyhub.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726111AbgJNT4Y (ORCPT ); Wed, 14 Oct 2020 15:56:24 -0400 Received: from zn.tnic (p200300ec2f0c4400a8a63b86eef17592.dip0.t-ipconnect.de [IPv6:2003:ec:2f0c:4400:a8a6:3b86:eef1:7592]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by mail.skyhub.de (SuperMail on ZX Spectrum 128k) with ESMTPSA id D459E1EC0493; Wed, 14 Oct 2020 21:56:22 +0200 (CEST) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=alien8.de; s=dkim; t=1602705383; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version:content-type:content-type: content-transfer-encoding:in-reply-to:in-reply-to: references:references; bh=kRhOfW32b0y55S8bP4pZaw8i53srY+meEMHsyHTonbQ=; b=rQa3QO0OIFdfmh14RpHCz+2MO2wmrwcAVseqnjcbTbZYLJR2OydUVQ0ZXx/QDMUG6FE1X4 AWT7XpgUlG94HWu20GZJRPMYLoGI6a3Fg0raNAFpBnkl3VIcIGBNk6zLf9CRNEgXfsW+QB oiGO7DH/3vHhksVtmdEUDM0zvJAirzE= Date: Wed, 14 Oct 2020 21:56:14 +0200 From: Borislav Petkov To: Ankur Arora Cc: linux-kernel@vger.kernel.org, linux-mm@kvack.org, kirill@shutemov.name, mhocko@kernel.org, boris.ostrovsky@oracle.com, konrad.wilk@oracle.com, Thomas Gleixner , Ingo Molnar , x86@kernel.org, "H. Peter Anvin" , Jiri Slaby , Herbert Xu , "Rafael J. Wysocki" Subject: Re: [PATCH 4/8] x86/asm: add clear_page_nt() Message-ID: <20201014195614.GB18196@zn.tnic> References: <20201014083300.19077-1-ankur.a.arora@oracle.com> <20201014083300.19077-5-ankur.a.arora@oracle.com> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline In-Reply-To: <20201014083300.19077-5-ankur.a.arora@oracle.com> Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Wed, Oct 14, 2020 at 01:32:55AM -0700, Ankur Arora wrote: > This can potentially improve page-clearing bandwidth (see below for > performance numbers for two microarchitectures where it helps and one > where it doesn't) and can help indirectly by consuming less cache > resources. > > Any performance benefits are expected for extents larger than LLC-sized > or more -- when we are DRAM-BW constrained rather than cache-BW > constrained. "potentially", "expected", I don't like those formulations. Do you have some actual benchmark data where this shows any improvement and not microbenchmarks only, to warrant the additional complexity? -- Regards/Gruss, Boris. https://people.kernel.org/tglx/notes-about-netiquette