From patchwork Fri Jan 12 17:41:19 2018 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: "Bodireddy, Bhanuprakash" X-Patchwork-Id: 860112 X-Patchwork-Delegate: ian.stokes@intel.com Return-Path: X-Original-To: incoming@patchwork.ozlabs.org Delivered-To: patchwork-incoming@bilbo.ozlabs.org Authentication-Results: ozlabs.org; spf=pass (mailfrom) smtp.mailfrom=openvswitch.org (client-ip=140.211.169.12; helo=mail.linuxfoundation.org; envelope-from=ovs-dev-bounces@openvswitch.org; receiver=) Received: from mail.linuxfoundation.org (mail.linuxfoundation.org [140.211.169.12]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by ozlabs.org (Postfix) with ESMTPS id 3zJ9Ng0h5Cz9sNV for ; Sat, 13 Jan 2018 04:54:11 +1100 (AEDT) Received: from mail.linux-foundation.org (localhost [127.0.0.1]) by mail.linuxfoundation.org (Postfix) with ESMTP id 34276F0D; Fri, 12 Jan 2018 17:52:44 +0000 (UTC) X-Original-To: dev@openvswitch.org Delivered-To: ovs-dev@mail.linuxfoundation.org Received: from smtp1.linuxfoundation.org (smtp1.linux-foundation.org [172.17.192.35]) by mail.linuxfoundation.org (Postfix) with ESMTPS id 19662ED4 for ; Fri, 12 Jan 2018 17:52:41 +0000 (UTC) X-Greylist: domain auto-whitelisted by SQLgrey-1.7.6 Received: from mga01.intel.com (mga01.intel.com [192.55.52.88]) by smtp1.linuxfoundation.org (Postfix) with ESMTPS id 9919E44D for ; Fri, 12 Jan 2018 17:52:40 +0000 (UTC) X-Amp-Result: SKIPPED(no attachment in message) X-Amp-File-Uploaded: False Received: from orsmga003.jf.intel.com ([10.7.209.27]) by fmsmga101.fm.intel.com with ESMTP/TLS/DHE-RSA-AES256-GCM-SHA384; 12 Jan 2018 09:52:40 -0800 X-ExtLoop1: 1 X-IronPort-AV: E=Sophos;i="5.46,350,1511856000"; d="scan'208";a="19631350" Received: from silpixa00393942.ir.intel.com (HELO silpixa00393942.ger.corp.intel.com) ([10.237.223.42]) by orsmga003.jf.intel.com with ESMTP; 12 Jan 2018 09:52:39 -0800 From: Bhanuprakash Bodireddy To: dev@openvswitch.org Date: Fri, 12 Jan 2018 17:41:19 +0000 Message-Id: <1515778879-60075-4-git-send-email-bhanuprakash.bodireddy@intel.com> X-Mailer: git-send-email 2.4.11 In-Reply-To: <1515778879-60075-1-git-send-email-bhanuprakash.bodireddy@intel.com> References: <1515778879-60075-1-git-send-email-bhanuprakash.bodireddy@intel.com> X-Spam-Status: No, score=-6.9 required=5.0 tests=BAYES_00, RCVD_IN_DNSWL_HI, T_RP_MATCHES_RCVD autolearn=ham version=3.3.1 X-Spam-Checker-Version: SpamAssassin 3.3.1 (2010-03-16) on smtp1.linux-foundation.org Subject: [ovs-dev] [PATCH 4/4] doc: Update configure section with prefetchwt1 details. X-BeenThere: ovs-dev@openvswitch.org X-Mailman-Version: 2.1.12 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , MIME-Version: 1.0 Sender: ovs-dev-bounces@openvswitch.org Errors-To: ovs-dev-bounces@openvswitch.org Inspite of specifying -march=native when using Low Temporal Write(OPCH_LTW), the compiler generates 'prefetchw' instruction instead of 'prefetchwt1' instruction available on processor as in 'Case B'. To make the compiler emit prefetchwt1 instruction, -mprefetchwt1 needs to be passed to configure explicitly. [Problem] Case A: OVS_PREFETCH_CACHE(addr, OPCH_HTW) [__builtin_prefetch(addr, 1, 3)] [Assembly] leaq -112(%rbp), %rax prefetchw (%rax) Case B: OVS_PREFETCH_CACHE(addr, OPCH_LTW) [__builtin_prefetch(addr, 1, 1)] [Assembly] leaq -112(%rbp), %rax prefetchw (%rax) <***problem***> [Solution] ./configure CFLAGS="-g -O2 -mprefetchwt1" Case B: OVS_PREFETCH_CACHE(addr, OPCH_LTW) [__builtin_prefetch(addr, 1, 1)] [Assembly] leaq -112(%rbp), %rax prefetchwt1 (%rax) See also: https://mail.openvswitch.org/pipermail/ovs-dev/2017-December/341591.html Signed-off-by: Bhanuprakash Bodireddy --- Documentation/intro/install/general.rst | 13 +++++++++++++ 1 file changed, 13 insertions(+) diff --git a/Documentation/intro/install/general.rst b/Documentation/intro/install/general.rst index 718e5c2..4d2db45 100644 --- a/Documentation/intro/install/general.rst +++ b/Documentation/intro/install/general.rst @@ -280,6 +280,19 @@ With this, GCC will detect the processor and automatically set appropriate flags for it. This should not be used if you are compiling OVS outside the target machine. +Compilers(gcc) won't emit prefetchwt1 instruction even with '-march=native' +specified. In such case, -mprefetchwt1 needs to be explicitly passed during +configuration. + +For example inspite of specifying -march=native when using Low Temporal Write +i.e OVS_PREFETCH_CACHE(addr, OPCH_LTW), the compiler generates 'prefetchw' +instruction instead of 'prefetchwt1' instruction available on processor. + +To make the compiler generate the appropriate instruction, it is recommended +to pass ``-mprefetchwt1`` settings:: + + $ ./configure CFLAGS="-g -O2 -march=native -mprefetchwt1" + .. note:: CFLAGS are not applied when building the Linux kernel module. Custom CFLAGS for the kernel module are supplied using the ``EXTRA_CFLAGS`` variable when