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=-2.5 required=3.0 tests=DKIMWL_WL_HIGH,DKIM_SIGNED, DKIM_VALID,MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS,URIBL_BLOCKED, 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 8D415C433E0 for ; Fri, 3 Jul 2020 16:22:57 +0000 (UTC) Received: from merlin.infradead.org (merlin.infradead.org [205.233.59.134]) (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 547AF20870 for ; Fri, 3 Jul 2020 16:22:57 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (2048-bit key) header.d=lists.infradead.org header.i=@lists.infradead.org header.b="A21SBfoA"; dkim=fail reason="signature verification failed" (1024-bit key) header.d=kernel.org header.i=@kernel.org header.b="qLAgdC6e" DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 547AF20870 Authentication-Results: mail.kernel.org; dmarc=fail (p=none dis=none) header.from=kernel.org 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=merlin.20170209; h=Sender:Content-Transfer-Encoding: Content-Type:Cc:List-Subscribe:List-Help:List-Post:List-Archive: List-Unsubscribe:List-Id:In-Reply-To:MIME-Version:References:Message-ID: Subject: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=OCrO27mTStZg6IeLCiOKDKgFlrdtloSua2qq/UgXH+g=; b=A21SBfoAJNcLLe5menPszVbkF C39wqj0aRmts8vlaX5h2eOgZmJ7OIZ5QmkdZH24DvGTxyvJWRPIZ/MMsdcXtJE/4Tsf7VdYEXVq5j c3Pu8wzyuU0WGVlqy5Jn4Lf1cheLba0ECWCa5e79bQFDB/2BpXWZuDHhBuTzdEpMQl0bjRT3Rz24d 7aOWE/ypm8pihdRBLFTTOmirQbL8lyUaD7qH9tabDkq8MfNKYQ/F4R4DKkPmU/p7X9dzNTo63Aub6 zmqawDxGgFzpNK4zbh7p7dtSmzvtf0RF+rzle7KkZMZWzgX8oEQFhUckLxZrQVkdHBWx9kIidMtyv wEtN5yRcg==; Received: from localhost ([::1] helo=merlin.infradead.org) by merlin.infradead.org with esmtp (Exim 4.92.3 #3 (Red Hat Linux)) id 1jrORd-0005h6-Dq; Fri, 03 Jul 2020 16:21:45 +0000 Received: from mail.kernel.org ([198.145.29.99]) by merlin.infradead.org with esmtps (Exim 4.92.3 #3 (Red Hat Linux)) id 1jrORb-0005gd-8f for linux-arm-kernel@lists.infradead.org; Fri, 03 Jul 2020 16:21:44 +0000 Received: from willie-the-truck (236.31.169.217.in-addr.arpa [217.169.31.236]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by mail.kernel.org (Postfix) with ESMTPSA id 330B020870; Fri, 3 Jul 2020 16:21:41 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1593793302; bh=NzfhRf3soxj5TQfIjjCSrbgU2QN4oP6jlNZFAvHuZOU=; h=Date:From:To:Cc:Subject:References:In-Reply-To:From; b=qLAgdC6ezL1L+Qj1hDr43/Lc0qG1m/WMRQEdKTPT7BAp4ExPpbZ46FN13dokZWmxE sqyNjMCz2MY0H0YP/cteR63+lSK1gnO68F5AWXmCutMVWi3VDZZp3whB24iM/exovw sRW/fvDrWluUp3xPS/smfAiSCWFZjCiJiprq9ptg= Date: Fri, 3 Jul 2020 17:21:38 +0100 From: Will Deacon To: Barry Song Subject: Re: [PATCH] iommu/arm-smmu-v3: expose numa_node attribute to users in sysfs Message-ID: <20200703162137.GA19780@willie-the-truck> References: <20200530091505.56664-1-song.bao.hua@hisilicon.com> MIME-Version: 1.0 Content-Disposition: inline In-Reply-To: <20200530091505.56664-1-song.bao.hua@hisilicon.com> User-Agent: Mutt/1.10.1 (2018-07-13) X-CRM114-Version: 20100106-BlameMichelson ( TRE 0.8.0 (BSD) ) MR-646709E3 X-CRM114-CacheID: sfid-20200703_122143_661222_5363AF94 X-CRM114-Status: GOOD ( 11.06 ) X-BeenThere: linux-arm-kernel@lists.infradead.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: linuxarm@huawei.com, iommu@lists.linux-foundation.org, robin.murphy@arm.com, hch@lst.de, linux-arm-kernel@lists.infradead.org, m.szyprowski@samsung.com 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 Sat, May 30, 2020 at 09:15:05PM +1200, Barry Song wrote: > As tests show the latency of dma_unmap can increase dramatically while > calling them cross NUMA nodes, especially cross CPU packages, eg. > 300ns vs 800ns while waiting for the completion of CMD_SYNC in an > empty command queue. The large latency causing by remote node will > in turn make contention of the command queue more serious, and enlarge > the latency of DMA users within local NUMA nodes. > > Users might intend to enforce NUMA locality with the consideration of > the position of SMMU. The patch provides minor benefit by presenting > this information to users directly, as they might want to know it without > checking hardware spec at all. I don't think that's a very good reason to expose things to userspace. I know sysfs shouldn't be treated as ABI, but the grim reality is that once somebody relies on this stuff then we can't change it, so I'd rather avoid exposing it unless it's absolutely necessary. Thanks, Will _______________________________________________ linux-arm-kernel mailing list linux-arm-kernel@lists.infradead.org http://lists.infradead.org/mailman/listinfo/linux-arm-kernel