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 1F5ADC1B0F1 for ; Tue, 19 Jun 2018 21:37:25 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id D6C102075E for ; Tue, 19 Jun 2018 21:37:24 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org D6C102075E Authentication-Results: mail.kernel.org; dmarc=fail (p=none dis=none) header.from=intel.com 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 S967344AbeFSVhX (ORCPT ); Tue, 19 Jun 2018 17:37:23 -0400 Received: from mga06.intel.com ([134.134.136.31]:1759 "EHLO mga06.intel.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S967205AbeFSVhL (ORCPT ); Tue, 19 Jun 2018 17:37:11 -0400 X-Amp-Result: UNSCANNABLE X-Amp-File-Uploaded: False Received: from orsmga003.jf.intel.com ([10.7.209.27]) by orsmga104.jf.intel.com with ESMTP/TLS/DHE-RSA-AES256-GCM-SHA384; 19 Jun 2018 14:37:10 -0700 X-ExtLoop1: 1 X-IronPort-AV: E=Sophos;i="5.51,244,1526367600"; d="scan'208";a="60583867" Received: from romley-ivt3.sc.intel.com ([172.25.110.60]) by orsmga003.jf.intel.com with ESMTP; 19 Jun 2018 14:37:10 -0700 Date: Tue, 19 Jun 2018 14:36:44 -0700 From: Fenghua Yu To: Thomas Gleixner Cc: Fenghua Yu , 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 Message-ID: <20180619213644.GC112652@romley-ivt3.sc.intel.com> References: <1529118375-90191-1-git-send-email-fenghua.yu@intel.com> <1529118375-90191-2-git-send-email-fenghua.yu@intel.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: User-Agent: Mutt/1.5.23 (2014-03-12) Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org 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. Thanks. -Fenghua