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=-8.2 required=3.0 tests=BAYES_00, HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,SIGNED_OFF_BY,SPF_HELO_NONE, SPF_PASS,URIBL_BLOCKED,USER_AGENT_SANE_1 autolearn=unavailable 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 184A4C433F2 for ; Fri, 10 Jul 2020 14:20:49 +0000 (UTC) Received: from hemlock.osuosl.org (smtp2.osuosl.org [140.211.166.133]) (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 DB31020674 for ; Fri, 10 Jul 2020 14:20:47 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org DB31020674 Authentication-Results: mail.kernel.org; dmarc=fail (p=none dis=none) header.from=8bytes.org Authentication-Results: mail.kernel.org; spf=pass smtp.mailfrom=iommu-bounces@lists.linux-foundation.org Received: from localhost (localhost [127.0.0.1]) by hemlock.osuosl.org (Postfix) with ESMTP id BF42689CB0; Fri, 10 Jul 2020 14:20:47 +0000 (UTC) X-Virus-Scanned: amavisd-new at osuosl.org Received: from hemlock.osuosl.org ([127.0.0.1]) by localhost (.osuosl.org [127.0.0.1]) (amavisd-new, port 10024) with ESMTP id iTAMrFL4SjL1; Fri, 10 Jul 2020 14:20:44 +0000 (UTC) Received: from lists.linuxfoundation.org (lf-lists.osuosl.org [140.211.9.56]) by hemlock.osuosl.org (Postfix) with ESMTP id 42B6489CB2; Fri, 10 Jul 2020 14:20:44 +0000 (UTC) Received: from lf-lists.osuosl.org (localhost [127.0.0.1]) by lists.linuxfoundation.org (Postfix) with ESMTP id 2F1A8C077B; Fri, 10 Jul 2020 14:20:44 +0000 (UTC) Received: from hemlock.osuosl.org (smtp2.osuosl.org [140.211.166.133]) by lists.linuxfoundation.org (Postfix) with ESMTP id 600FFC016F for ; Fri, 10 Jul 2020 14:20:42 +0000 (UTC) Received: from localhost (localhost [127.0.0.1]) by hemlock.osuosl.org (Postfix) with ESMTP id 4E48789CB0 for ; Fri, 10 Jul 2020 14:20:42 +0000 (UTC) X-Virus-Scanned: amavisd-new at osuosl.org Received: from hemlock.osuosl.org ([127.0.0.1]) by localhost (.osuosl.org [127.0.0.1]) (amavisd-new, port 10024) with ESMTP id NcINOp2m3FpJ for ; Fri, 10 Jul 2020 14:20:40 +0000 (UTC) X-Greylist: from auto-whitelisted by SQLgrey-1.7.6 Received: from theia.8bytes.org (8bytes.org [81.169.241.247]) by hemlock.osuosl.org (Postfix) with ESMTPS id 20D7089CB8 for ; Fri, 10 Jul 2020 14:20:40 +0000 (UTC) Received: by theia.8bytes.org (Postfix, from userid 1000) id 990CB20C; Fri, 10 Jul 2020 16:20:38 +0200 (CEST) Date: Fri, 10 Jul 2020 16:20:37 +0200 From: Joerg Roedel To: Robin Murphy Subject: Re: [PATCH 1/2] iommu/intel: Avoid SAC address trick for PCIe devices Message-ID: <20200710142037.GM27672@8bytes.org> References: MIME-Version: 1.0 Content-Disposition: inline In-Reply-To: User-Agent: Mutt/1.10.1 (2018-07-13) Cc: linux-pci@vger.kernel.org, linux-kernel@vger.kernel.org, iommu@lists.linux-foundation.org, jonathan.lemon@gmail.com, dwmw2@infradead.org, hch@lst.de, linux-arm-kernel@lists.infradead.org X-BeenThere: iommu@lists.linux-foundation.org X-Mailman-Version: 2.1.15 Precedence: list List-Id: Development issues for Linux IOMMU support List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Errors-To: iommu-bounces@lists.linux-foundation.org Sender: "iommu" On Wed, Jul 08, 2020 at 12:32:41PM +0100, Robin Murphy wrote: > For devices stuck behind a conventional PCI bus, saving extra cycles at > 33MHz is probably fairly significant. However since native PCI Express > is now the norm for high-performance devices, the optimisation to always > prefer 32-bit addresses for the sake of avoiding DAC is starting to look > rather anachronistic. Technically 32-bit addresses do have shorter TLPs > on PCIe, but unless the device is saturating its link bandwidth with > small transfers it seems unlikely that the difference is appreciable. > > What definitely is appreciable, however, is that the IOVA allocator > doesn't behave all that well once the 32-bit space starts getting full. > As DMA working sets get bigger, this optimisation increasingly backfires > and adds considerable overhead to the dma_map path for use-cases like > high-bandwidth networking. > > As such, let's simply take it out of consideration for PCIe devices. > Technically this might work out suboptimal for a PCIe device stuck > behind a conventional PCI bridge, or for PCI-X devices that also have > native 64-bit addressing, but neither of those are likely to be found > in performance-critical parts of modern systems. > > Signed-off-by: Robin Murphy > --- > drivers/iommu/intel/iommu.c | 3 ++- > 1 file changed, 2 insertions(+), 1 deletion(-) Applied both, thanks. _______________________________________________ iommu mailing list iommu@lists.linux-foundation.org https://lists.linuxfoundation.org/mailman/listinfo/iommu