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=-2.2 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS,USER_AGENT_SANE_1 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 5566CC432C3 for ; Wed, 20 Nov 2019 23:46:56 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 2304220715 for ; Wed, 20 Nov 2019 23:46:56 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1725936AbfKTXqz (ORCPT ); Wed, 20 Nov 2019 18:46:55 -0500 Received: from mga07.intel.com ([134.134.136.100]:19050 "EHLO mga07.intel.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1725878AbfKTXqz (ORCPT ); Wed, 20 Nov 2019 18:46:55 -0500 X-Amp-Result: SKIPPED(no attachment in message) X-Amp-File-Uploaded: False Received: from fmsmga007.fm.intel.com ([10.253.24.52]) by orsmga105.jf.intel.com with ESMTP/TLS/DHE-RSA-AES256-GCM-SHA384; 20 Nov 2019 15:46:55 -0800 X-ExtLoop1: 1 X-IronPort-AV: E=Sophos;i="5.69,223,1571727600"; d="scan'208";a="204980377" Received: from djiang5-desk3.ch.intel.com ([143.182.136.137]) by fmsmga007.fm.intel.com with ESMTP; 20 Nov 2019 15:46:53 -0800 Subject: Re: [PATCH RFC 01/14] x86/asm: add iosubmit_cmds512() based on movdir64b CPU instruction To: "Hansen, Dave" , "dmaengine@vger.kernel.org" , "linux-kernel@vger.kernel.org" , "vkoul@kernel.org" Cc: "Williams, Dan J" , "Luck, Tony" , "Lin, Jing" , "Raj, Ashok" , "Kumar, Sanjay K" , "Dey, Megha" , "Pan, Jacob jun" , "Liu, Yi L" , "axboe@kernel.dk" , "akpm@linux-foundation.org" , "tglx@linutronix.de" , "mingo@redhat.com" , "bp@alien8.de" , "Yu, Fenghua" , "hpa@zytor.com" References: <157428480574.36836.14057238306923901253.stgit@djiang5-desk3.ch.intel.com> <157428502934.36836.8119026517510193201.stgit@djiang5-desk3.ch.intel.com> <8f860476-24e4-6e03-752b-10a59aed8901@intel.com> From: Dave Jiang Message-ID: <7d3ba8bb-fbb6-097c-fa5a-6b3ec21f72e3@intel.com> Date: Wed, 20 Nov 2019 16:46:53 -0700 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:68.0) Gecko/20100101 Thunderbird/68.1.1 MIME-Version: 1.0 In-Reply-To: <8f860476-24e4-6e03-752b-10a59aed8901@intel.com> Content-Type: text/plain; charset=utf-8; format=flowed Content-Language: en-US Content-Transfer-Encoding: 7bit Sender: dmaengine-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: dmaengine@vger.kernel.org On 11/20/19 2:50 PM, Hansen, Dave wrote: > On 11/20/19 1:23 PM, Dave Jiang wrote: >> +static inline void __iowrite512(void __iomem *__dst, const void *src) >> +{ >> + volatile struct { char _[64]; } *dst = __dst; > > This _looks_ like gibberish. I know it's not, but it is subtle enough > that it really needs specific comments. I'll add comments explaining. > >> +static inline void iosubmit_cmds512(void __iomem *dst, const void *src, >> + size_t count) >> +{ >> + const u8 *from = src; >> + const u8 *end = from + count * 64; >> + >> + if (!cpu_has_write512()) >> + return; >> + >> + while (from < end) { >> + __iowrite512(dst, from); >> + from += 64; >> + } >> +} > > Won't this silently just drop things if the CPU doesn't have movdir64b > support? > > It seems like this shouldn't be called at all if > !cpu_has_write512(), but wouldn't something like this be mroe appropriate? > > if (!cpu_has_write512()) { > WARN_ON_ONCE(1); > return; > } > > Is the caller just supposed to infer that "dst" was never overwritten? > Thanks. I'll add the WARN().