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=-0.8 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,SPF_PASS autolearn=ham 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 D5062C1B0F1 for ; Tue, 19 Jun 2018 22:32:39 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 88DB320661 for ; Tue, 19 Jun 2018 22:32:39 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 88DB320661 Authentication-Results: mail.kernel.org; dmarc=none (p=none dis=none) header.from=linutronix.de Authentication-Results: mail.kernel.org; spf=none smtp.mailfrom=linux-kernel-owner@vger.kernel.org Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754093AbeFSWch (ORCPT ); Tue, 19 Jun 2018 18:32:37 -0400 Received: from Galois.linutronix.de ([146.0.238.70]:58458 "EHLO Galois.linutronix.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1750973AbeFSWce (ORCPT ); Tue, 19 Jun 2018 18:32:34 -0400 Received: from p4fea482e.dip0.t-ipconnect.de ([79.234.72.46] helo=nanos.glx-home) by Galois.linutronix.de with esmtpsa (TLS1.2:DHE_RSA_AES_256_CBC_SHA256:256) (Exim 4.80) (envelope-from ) id 1fVPAc-0004iO-Ov; Wed, 20 Jun 2018 00:32:14 +0200 Date: Wed, 20 Jun 2018 00:32:14 +0200 (CEST) From: Thomas Gleixner To: Fenghua Yu cc: Ingo Molnar , H Peter Anvin , Ashok Raj , Alan Cox , Ravi V Shankar , linux-kernel , x86 Subject: Re: [RFC PATCH 1/8] x86/cpufeatures: Enumerate MOVDIRI instruction In-Reply-To: <20180619213644.GC112652@romley-ivt3.sc.intel.com> Message-ID: References: <1529118375-90191-1-git-send-email-fenghua.yu@intel.com> <1529118375-90191-2-git-send-email-fenghua.yu@intel.com> <20180619213644.GC112652@romley-ivt3.sc.intel.com> User-Agent: Alpine 2.21 (DEB 202 2017-01-01) MIME-Version: 1.0 Content-Type: text/plain; charset=US-ASCII X-Linutronix-Spam-Score: -1.0 X-Linutronix-Spam-Level: - X-Linutronix-Spam-Status: No , -1.0 points, 5.0 required, ALL_TRUSTED=-1,SHORTCIRCUIT=-0.0001 Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Tue, 19 Jun 2018, Fenghua Yu wrote: > On Tue, Jun 19, 2018 at 10:57:44AM +0200, Thomas Gleixner wrote: > > On Fri, 15 Jun 2018, Fenghua Yu wrote: > > > > > MOVDIRI moves doubleword or quadword from register to memory through > > > direct store which is implemented by using write combining (WC) for > > > writing data directly into memory without caching the data. > > > > And that is useful for what? > > Programmable agents can handle streaming offload (e.g. high speed packet > processing in network). Hardware implements a doorbell (tail pointer) > register that is updated by software when adding new work-elements to > the streaming offload work-queue. > > MOVDIRI can be used as the doorbell write which is a 4-byte or 8-byte > uncachable write to MMIO. MOVDIRI has lower overhead than other ways > to write the doorbell. > > In low latency offload (e.g. Non-Volatile Memory, etc), MOVDIR64B writes > work descriptors (and data in some cases) to device-hosted work-queues > with atomicity. Makes sense, but why is this not part of the changelog ? Thanks, tglx