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=-1.0 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,SPF_PASS autolearn=ham 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 59473C10F0E for ; Fri, 12 Apr 2019 12:12:42 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 2F690206BA for ; Fri, 12 Apr 2019 12:12:42 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726736AbfDLMMl (ORCPT ); Fri, 12 Apr 2019 08:12:41 -0400 Received: from mx0a-001b2d01.pphosted.com ([148.163.156.1]:58810 "EHLO mx0a-001b2d01.pphosted.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726327AbfDLMMk (ORCPT ); Fri, 12 Apr 2019 08:12:40 -0400 Received: from pps.filterd (m0098399.ppops.net [127.0.0.1]) by mx0a-001b2d01.pphosted.com (8.16.0.27/8.16.0.27) with SMTP id x3CC6OH6122933 for ; Fri, 12 Apr 2019 08:12:39 -0400 Received: from e06smtp07.uk.ibm.com (e06smtp07.uk.ibm.com [195.75.94.103]) by mx0a-001b2d01.pphosted.com with ESMTP id 2rts0qbwja-1 (version=TLSv1.2 cipher=AES256-GCM-SHA384 bits=256 verify=NOT) for ; Fri, 12 Apr 2019 08:12:39 -0400 Received: from localhost by e06smtp07.uk.ibm.com with IBM ESMTP SMTP Gateway: Authorized Use Only! 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Violators will be prosecuted; (version=TLSv1/SSLv3 cipher=AES256-GCM-SHA384 bits=256/256) Fri, 12 Apr 2019 13:12:34 +0100 Received: from d06av25.portsmouth.uk.ibm.com (d06av25.portsmouth.uk.ibm.com [9.149.105.61]) by b06cxnps4075.portsmouth.uk.ibm.com (8.14.9/8.14.9/NCO v10.0) with ESMTP id x3CCCWKu52101274 (version=TLSv1/SSLv3 cipher=DHE-RSA-AES256-GCM-SHA384 bits=256 verify=OK); Fri, 12 Apr 2019 12:12:33 GMT Received: from d06av25.portsmouth.uk.ibm.com (unknown [127.0.0.1]) by IMSVA (Postfix) with ESMTP id CAA1611C054; Fri, 12 Apr 2019 12:12:32 +0000 (GMT) Received: from d06av25.portsmouth.uk.ibm.com (unknown [127.0.0.1]) by IMSVA (Postfix) with ESMTP id 6493111C058; Fri, 12 Apr 2019 12:12:32 +0000 (GMT) Received: from dyn-9-152-212-186.boeblingen.de.ibm.com (unknown [9.152.212.186]) by d06av25.portsmouth.uk.ibm.com (Postfix) with ESMTPS; Fri, 12 Apr 2019 12:12:32 +0000 (GMT) Date: Fri, 12 Apr 2019 14:12:31 +0200 (CEST) From: Sebastian Ott X-X-Sender: sebott@schleppi To: Halil Pasic cc: kvm@vger.kernel.org, linux-s390@vger.kernel.org, Cornelia Huck , Martin Schwidefsky , virtualization@lists.linux-foundation.org, Christian Borntraeger , Viktor Mihajlovski , Vasily Gorbik , Janosch Frank , Claudio Imbrenda , Farhan Ali , Eric Farman Subject: Re: [RFC PATCH 04/12] s390/cio: introduce cio DMA pool In-Reply-To: <20190412132010.3c74cb63@oc2783563651> References: <20190404231622.52531-1-pasic@linux.ibm.com> <20190404231622.52531-5-pasic@linux.ibm.com> <20190412132010.3c74cb63@oc2783563651> User-Agent: Alpine 2.21 (LFD 202 2017-01-01) Organization: =?ISO-8859-15?Q?=22IBM_Deutschland_Research_&_Development_GmbH?= =?ISO-8859-15?Q?_=2F_Vorsitzende_des_Aufsichtsrats=3A_Matthias?= =?ISO-8859-15?Q?_Hartmann_Gesch=E4ftsf=FChrung=3A_Dirk_Wittkopp?= =?ISO-8859-15?Q?_Sitz_der_Gesellschaft=3A_B=F6blingen_=2F_Reg?= =?ISO-8859-15?Q?istergericht=3A_Amtsgericht_Stuttgart=2C_HRB_2432?= =?ISO-8859-15?Q?94=22?= MIME-Version: 1.0 Content-Type: text/plain; charset=US-ASCII X-TM-AS-GCONF: 00 x-cbid: 19041212-0028-0000-0000-000003601C6C X-IBM-AV-DETECTION: SAVI=unused REMOTE=unused XFE=unused x-cbparentid: 19041212-0029-0000-0000-0000241F476A Message-Id: X-Proofpoint-Virus-Version: vendor=fsecure engine=2.50.10434:,, definitions=2019-04-12_08:,, signatures=0 X-Proofpoint-Spam-Details: rule=outbound_notspam policy=outbound score=0 priorityscore=1501 malwarescore=0 suspectscore=3 phishscore=0 bulkscore=0 spamscore=0 clxscore=1015 lowpriorityscore=0 mlxscore=0 impostorscore=0 mlxlogscore=772 adultscore=0 classifier=spam adjust=0 reason=mlx scancount=1 engine=8.0.1-1810050000 definitions=main-1904120080 Sender: kvm-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: kvm@vger.kernel.org On Fri, 12 Apr 2019, Halil Pasic wrote: > On Thu, 11 Apr 2019 20:25:01 +0200 (CEST) > Sebastian Ott wrote: > > I don't think we should use this global DMA pool. I guess it's OK for > > stuff like airq (where we don't have a struct device at hand) but for > > CCW we should use the device we have. Yes, this way we waste some memory > > but all dma memory a device uses should fit in a page - so the wastage > > is not too much. > > > > Is what you envision an own gen_pool on for each subchannel (e.g. a > struct io_subchannel member)? Either that or if that's too much overhead simply map a page and create a struct containing the few dma areas for that device. > I'm struggling with understanding the expected benefits of a > per-subchannel pool/allocator. Can you please tell me what benefits do > you expect (over the current approach)? Logically DMA is a capability of a device and the whole DMA API is build around devices. Working around that just feels wrong. For practical matters: DMA debugging will complain about misuse of a specific device or driver. > I understand you idea is to keep the CIO global pool for stuff that can > not be tied to a single device (i.e. ariq). So the per device stuff would > also mean more code. Would you be OK with postponing this alleged > enhancement (i.e. implement it as a patch on top of this series)? I don't like it but it's just in-kernel usage which we can change at any time. So if it helps you to do it that way, why not..