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=-5.2 required=3.0 tests=BAYES_00, HEADER_FROM_DIFFERENT_DOMAINS,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 CFE84C388F9 for ; Thu, 19 Nov 2020 07:54:48 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 7F3AC2220B for ; Thu, 19 Nov 2020 07:54:48 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726424AbgKSHy1 (ORCPT ); Thu, 19 Nov 2020 02:54:27 -0500 Received: from verein.lst.de ([213.95.11.211]:37888 "EHLO verein.lst.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1725813AbgKSHy1 (ORCPT ); Thu, 19 Nov 2020 02:54:27 -0500 Received: by verein.lst.de (Postfix, from userid 2407) id 5338667373; Thu, 19 Nov 2020 08:54:23 +0100 (CET) Date: Thu, 19 Nov 2020 08:54:22 +0100 From: Christoph Hellwig To: Ashish Kalra Cc: konrad.wilk@oracle.com, hch@lst.de, tglx@linutronix.de, mingo@redhat.com, bp@alien8.de, hpa@zytor.com, x86@kernel.org, luto@kernel.org, peterz@infradead.org, dave.hansen@linux-intel.com, iommu@lists.linux-foundation.org, linux-kernel@vger.kernel.org, brijesh.singh@amd.com, Thomas.Lendacky@amd.com, jon.grimm@amd.com, rientjes@google.com Subject: Re: [PATCH v5] swiotlb: Adjust SWIOTBL bounce buffer size for SEV guests. Message-ID: <20201119075422.GA15840@lst.de> References: <20201118201243.18510-1-Ashish.Kalra@amd.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20201118201243.18510-1-Ashish.Kalra@amd.com> User-Agent: Mutt/1.5.17 (2007-11-01) Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Wed, Nov 18, 2020 at 08:12:43PM +0000, Ashish Kalra wrote: > From: Ashish Kalra > > For SEV, all DMA to and from guest has to use shared > (un-encrypted) pages. SEV uses SWIOTLB to make this > happen without requiring changes to device drivers. > However, depending on workload being run, the default > 64MB of SWIOTLB might not be enough and SWIOTLB > may run out of buffers to use for DMA, resulting > in I/O errors and/or performance degradation for > high I/O workloads. FYI, you can use up 73 chars for your commit log. This looks rather compressed.