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=-4.0 required=3.0 tests=BAYES_00,DKIMWL_WL_HIGH, DKIM_SIGNED,DKIM_VALID,HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI, SPF_HELO_NONE,SPF_PASS,URIBL_BLOCKED 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 DAC47C2B9F4 for ; Tue, 22 Jun 2021 12:34:41 +0000 (UTC) Received: from bombadil.infradead.org (bombadil.infradead.org [198.137.202.133]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by mail.kernel.org (Postfix) with ESMTPS id A153561107 for ; Tue, 22 Jun 2021 12:34:41 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org A153561107 Authentication-Results: mail.kernel.org; dmarc=fail (p=none dis=none) header.from=arm.com Authentication-Results: mail.kernel.org; spf=none smtp.mailfrom=linux-arm-kernel-bounces+linux-arm-kernel=archiver.kernel.org@lists.infradead.org DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=lists.infradead.org; s=bombadil.20210309; h=Sender: Content-Transfer-Encoding:Content-Type:List-Subscribe:List-Help:List-Post: List-Archive:List-Unsubscribe:List-Id:In-Reply-To:MIME-Version:References: Message-ID:Subject:Cc:To:From:Date:Reply-To:Content-ID:Content-Description: Resent-Date:Resent-From:Resent-Sender:Resent-To:Resent-Cc:Resent-Message-ID: List-Owner; bh=T20BaOuOfOGCa30e0D+0qLg/u8/yOm8JOqfTpKLONLQ=; b=0vRWokz2PJQmd4 wYrKeRofoJIhZdLgYR+4RZS7td12l1TKuMH6r2QMVkJDo5MwpUCkz44LadqlzgAk/Q/viqNjLNfqv tHZXBNfDNOMDuLiy352UFXXU9lMAyoPm2B4cY4tOejam0hlzZWa14A6RfVVLL8MOhFQ8zHWHz8hra WDnUl0qBifNFwaAm4UIGxPVYdlYxy64jiy51hUcmyFIn46GhPW0MYhU561jcqAg5C7J99HI579cqX qK7zY9Sd8DZgEfgsxt5fHHpYCIfVZO/7hfOmtLjvAvqSFq6T6QtVuet/MJyBqXFUwTgbL302Q7Fxp VlHJjxasXL8JgTGJdPCg==; Received: from localhost ([::1] helo=bombadil.infradead.org) by bombadil.infradead.org with esmtp (Exim 4.94.2 #2 (Red Hat Linux)) id 1lvfal-0079KH-9J; Tue, 22 Jun 2021 12:33:23 +0000 Received: from foss.arm.com ([217.140.110.172]) by bombadil.infradead.org with esmtp (Exim 4.94.2 #2 (Red Hat Linux)) id 1lvfah-0079JX-PC for linux-arm-kernel@lists.infradead.org; Tue, 22 Jun 2021 12:33:21 +0000 Received: from usa-sjc-imap-foss1.foss.arm.com (unknown [10.121.207.14]) by usa-sjc-mx-foss1.foss.arm.com (Postfix) with ESMTP id 5DDE8ED1; Tue, 22 Jun 2021 05:33:18 -0700 (PDT) Received: from C02TD0UTHF1T.local (unknown [10.57.10.229]) by usa-sjc-imap-foss1.foss.arm.com (Postfix) with ESMTPSA id 78E0C3F694; Tue, 22 Jun 2021 05:33:15 -0700 (PDT) Date: Tue, 22 Jun 2021 13:32:21 +0100 From: Mark Rutland To: Will Deacon Cc: Guangbin Huang , davem@davemloft.net, kuba@kernel.org, catalin.marinas@arm.com, maz@kernel.org, dbrazdil@google.com, qperret@google.com, netdev@vger.kernel.org, linux-kernel@vger.kernel.org, linux-arm-kernel@lists.infradead.org, lipeng321@huawei.com, peterz@infradead.org Subject: Re: [PATCH net-next 1/3] arm64: barrier: add DGH macros to control memory accesses merging Message-ID: <20210622123221.GA71782@C02TD0UTHF1T.local> References: <1624360271-17525-1-git-send-email-huangguangbin2@huawei.com> <1624360271-17525-2-git-send-email-huangguangbin2@huawei.com> <20210622121630.GC30757@willie-the-truck> MIME-Version: 1.0 Content-Disposition: inline In-Reply-To: <20210622121630.GC30757@willie-the-truck> X-CRM114-Version: 20100106-BlameMichelson ( TRE 0.8.0 (BSD) ) MR-646709E3 X-CRM114-CacheID: sfid-20210622_053319_909686_08EA1066 X-CRM114-Status: GOOD ( 16.92 ) X-BeenThere: linux-arm-kernel@lists.infradead.org X-Mailman-Version: 2.1.34 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Sender: "linux-arm-kernel" Errors-To: linux-arm-kernel-bounces+linux-arm-kernel=archiver.kernel.org@lists.infradead.org On Tue, Jun 22, 2021 at 01:16:31PM +0100, Will Deacon wrote: > On Tue, Jun 22, 2021 at 07:11:09PM +0800, Guangbin Huang wrote: > > From: Xiongfeng Wang > > > > DGH prohibits merging memory accesses with Normal-NC or Device-GRE > > attributes before the hint instruction with any memory accesses > > appearing after the hint instruction. Provide macros to expose it to the > > arch code. > > Hmm. > > The architecture states: > > | DGH is a hint instruction. A DGH instruction is not expected to be > | performance optimal to merge memory accesses with Normal Non-cacheable > | or Device-GRE attributes appearing in program order before the hint > | instruction with any memory accesses appearing after the hint instruction > | into a single memory transaction on an interconnect. > > which doesn't make a whole lot of sense to me, in all honesty. I think there are some missing words, and this was supposed to say something like: | DGH is a hint instruction. A DGH instruction *indicates that it* is | not expected to be performance optimal to merge memory accesses with | Normal Non-cacheable or Device-GRE attributes appearing in program | order before the hint instruction with any memory accesses appearing | after the hint instruction into a single memory transaction on an | interconnect. ... i.e. it's a hint to the CPU to avoid merging accesses which are either side of the DGH, so that the prior accesses don't get indefinitely delayed waiting to be merged. I'll try to get the documentation fixed, since as-is the wording does not make sense. Thanks, Mark. _______________________________________________ linux-arm-kernel mailing list linux-arm-kernel@lists.infradead.org http://lists.infradead.org/mailman/listinfo/linux-arm-kernel