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Thunderbird/102.6.1 Subject: Re: [LSF/MM/BPF ATTEND][LSF/MM/BPF Topic] Non-block IO To: Bart Van Assche , Kanchan Joshi , lsf-pc@lists.linux-foundation.org Cc: linux-block@vger.kernel.org, linux-nvme@lists.infradead.org, io-uring@vger.kernel.org, axboe@kernel.dk, hch@lst.de, kbusch@kernel.org, ming.lei@redhat.com References: <20230210180033.321377-1-joshi.k@samsung.com> <69443f85-5e16-e3db-23e9-caf915881c92@acm.org> Content-Language: en-US From: John Garry Organization: Oracle Corporation In-Reply-To: <69443f85-5e16-e3db-23e9-caf915881c92@acm.org> Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 8bit X-ClientProxiedBy: LO4P265CA0183.GBRP265.PROD.OUTLOOK.COM (2603:10a6:600:311::6) To DM6PR10MB4313.namprd10.prod.outlook.com (2603:10b6:5:212::20) MIME-Version: 1.0 X-MS-PublicTrafficType: Email X-MS-TrafficTypeDiagnostic: DM6PR10MB4313:EE_|PH8PR10MB6575:EE_ X-MS-Office365-Filtering-Correlation-Id: 98976e61-2343-4f64-1e5c-08db0e76e859 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PH8PR10MB6575 X-Proofpoint-Virus-Version: vendor=baseguard engine=ICAP:2.0.219,Aquarius:18.0.930,Hydra:6.0.562,FMLib:17.11.170.22 definitions=2023-02-14_06,2023-02-14_01,2023-02-09_01 X-Proofpoint-Spam-Details: rule=notspam policy=default score=0 adultscore=0 suspectscore=0 phishscore=0 spamscore=0 bulkscore=0 mlxlogscore=919 malwarescore=0 mlxscore=0 classifier=spam adjust=0 reason=mlx scancount=1 engine=8.12.0-2212070000 definitions=main-2302140090 X-Proofpoint-GUID: Ko1DnCkifV9HSOoXWWmsnMydB1x9UqKm X-Proofpoint-ORIG-GUID: Ko1DnCkifV9HSOoXWWmsnMydB1x9UqKm Precedence: bulk List-ID: X-Mailing-List: io-uring@vger.kernel.org On 10/02/2023 18:18, Bart Van Assche wrote: > On 2/10/23 10:00, Kanchan Joshi wrote: >> 3. DMA cost: is high in presence of IOMMU. Keith posted the work[1], >> with block IO path, last year. I imagine plumbing to get a bit simpler >> with passthrough-only support. But what are the other things that must >> be sorted out to have progress on moving DMA cost out of the fast path? > > Are performance numbers available? > > Isn't IOMMU cost something that has already been solved? From > https://www.usenix.org/system/files/conference/atc15/atc15-paper-peleg.pdf: "Evaluation of our designs under Linux shows that (1) > they achieve 88.5%–100% of the performance obtained > without an IOMMU". That paper is ~8 years old now. Some recommendations are already supported in the kernel since then, like per-CPU IOVA caching and per-IOMMU domain IOTLB flushing with per-CPU queues (which is relevant to lazy mode only). Thanks, John