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 94FA1C10F11 for ; Wed, 10 Apr 2019 16:52:26 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 639DB20818 for ; Wed, 10 Apr 2019 16:52:26 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S2388096AbfDJQwZ (ORCPT ); Wed, 10 Apr 2019 12:52:25 -0400 Received: from mx0a-001b2d01.pphosted.com ([148.163.156.1]:42852 "EHLO mx0a-001b2d01.pphosted.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1727020AbfDJQwY (ORCPT ); Wed, 10 Apr 2019 12:52:24 -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 x3AGnBOU100647 for ; Wed, 10 Apr 2019 12:52:24 -0400 Received: from e06smtp04.uk.ibm.com (e06smtp04.uk.ibm.com [195.75.94.100]) by mx0a-001b2d01.pphosted.com with ESMTP id 2rskxts644-1 (version=TLSv1.2 cipher=AES256-GCM-SHA384 bits=256 verify=NOT) for ; Wed, 10 Apr 2019 12:52:23 -0400 Received: from localhost by e06smtp04.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) Wed, 10 Apr 2019 17:52:18 +0100 Received: from d06av24.portsmouth.uk.ibm.com (mk.ibm.com [9.149.105.60]) by b06cxnps4074.portsmouth.uk.ibm.com (8.14.9/8.14.9/NCO v10.0) with ESMTP id x3AGqGw546858306 (version=TLSv1/SSLv3 cipher=DHE-RSA-AES256-GCM-SHA384 bits=256 verify=OK); Wed, 10 Apr 2019 16:52:16 GMT Received: from d06av24.portsmouth.uk.ibm.com (unknown [127.0.0.1]) by IMSVA (Postfix) with ESMTP id 9D04042045; Wed, 10 Apr 2019 16:52:16 +0000 (GMT) Received: from d06av24.portsmouth.uk.ibm.com (unknown [127.0.0.1]) by IMSVA (Postfix) with ESMTP id 2765642047; Wed, 10 Apr 2019 16:52:16 +0000 (GMT) Received: from oc2783563651 (unknown [9.152.224.40]) by d06av24.portsmouth.uk.ibm.com (Postfix) with ESMTP; Wed, 10 Apr 2019 16:52:16 +0000 (GMT) Date: Wed, 10 Apr 2019 18:52:14 +0200 From: Halil Pasic To: Cornelia Huck Cc: kvm@vger.kernel.org, linux-s390@vger.kernel.org, Martin Schwidefsky , Sebastian Ott , 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: <20190410180719.17c3469e.cohuck@redhat.com> References: <20190404231622.52531-1-pasic@linux.ibm.com> <20190404231622.52531-5-pasic@linux.ibm.com> <20190409124458.348d1ff5.cohuck@redhat.com> <20190409141114.7dcce94a@oc2783563651> <20190409191453.01444317.cohuck@redhat.com> <20190410173148.067555dc@oc2783563651> <20190410180719.17c3469e.cohuck@redhat.com> Organization: IBM X-Mailer: Claws Mail 3.11.1 (GTK+ 2.24.31; x86_64-redhat-linux-gnu) MIME-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit X-TM-AS-GCONF: 00 x-cbid: 19041016-0016-0000-0000-0000026D6A16 X-IBM-AV-DETECTION: SAVI=unused REMOTE=unused XFE=unused x-cbparentid: 19041016-0017-0000-0000-000032C99ACF Message-Id: <20190410185214.7ac37c87@oc2783563651> X-Proofpoint-Virus-Version: vendor=fsecure engine=2.50.10434:,, definitions=2019-04-10_07:,, signatures=0 X-Proofpoint-Spam-Details: rule=outbound_notspam policy=outbound score=0 priorityscore=1501 malwarescore=0 suspectscore=0 phishscore=0 bulkscore=0 spamscore=0 clxscore=1015 lowpriorityscore=0 mlxscore=0 impostorscore=0 mlxlogscore=999 adultscore=0 classifier=spam adjust=0 reason=mlx scancount=1 engine=8.0.1-1810050000 definitions=main-1904100114 Sender: kvm-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: kvm@vger.kernel.org On Wed, 10 Apr 2019 18:07:19 +0200 Cornelia Huck wrote: > On Wed, 10 Apr 2019 17:31:48 +0200 > Halil Pasic wrote: > > > On Tue, 9 Apr 2019 19:14:53 +0200 > > Cornelia Huck wrote: > > > > [..] > > > > > > > At this point, you're always going via the css0 device. I'm > > > > > wondering whether you should pass in the cssid here and use > > > > > css_by_id(cssid) to make this future proof. But then, I'm not > > > > > quite clear from which context this will be called. > > > > > > > > As said before I don't see MCSS-E coming. Regarding the client code, > > > > please check out the rest of the series. Especially patch 6. > > > > > > > > From my perspective it would be at this stage saner to make it more > > > > obvious that only one css is supported (at the moment), than to > > > > implement MCSS-E, or to make this (kind of) MCSS-E ready. > > > > > > I disagree. I think there's value in keeping the interfaces clean > > > (within reasonable bounds, of course.) Even if there is no > > > implementation of MCSS-E other than QEMU... it is probably a good idea > > > to spend some brain cycles to make this conceptually clean. > > > > AFAIU Linux currently does not support MCSS-E. I don't have the > > bandwidth to implement MCSS-E support in the kernel. > > > > I fully agree for external interfaces should be MCSS-E conform, so > > should we ever decide to implement we don't have to overcome self-made > > obstacles. > > > > Kernel internal stuff however, IMHO, should avoid carrying a ballast of > > an 20%-30% implemented MCSS-E support. I see no benefit. > > > > But I don't insist. If you have a good idea how to make this more MCSS-E > > conform, you are welcome. In think something like this is best done on > > top of a series that provides a basic working solution. Especially if the > > conceptually clean thing is conceptually or code-wise more complex than > > the basic solution. If you have something in mind that is simpler and > > more lightweight than what I did here, I would be more than happy to make > > that happen. > > I haven't asked for adding complete support for MCSS-E, just to keep it > in the back of our minds... I will, I promise ;)! > > Back to the issue at hand. You're currently hard-wiring this to the > css0 device. My question is: Does it make sense to have a per-css area? What do you mean by area? > From my limited perspective, I think it does (more css images would > mean more devices, and just adding smaller areas per-css is probably > easier than adding one big area scaling with the number of css images). Currently all devices are hooked up to css0. This is also hard-wired: int css_register_subchannel(struct subchannel *sch) { int ret; /* Initialize the subchannel structure */ sch->dev.parent = &channel_subsystems[0]->device; I think the hard-wiring the DMA properties of the CSS to channel_subsystems[0] is consistent with prior art. > In that case, what about tacking the area to the actual css object, > instead of having the global variable? Should be an easy change, and > feels cleaner. > I already got rid of the global variable. Instead we have an accessor now. My problem with a gen_pool per ccs approach is the airq aiv vectors. Those vectors are currently shared between devices (at least for virtio-ccw), and those vectors must be allocated as shared (DMA) memory. Please take another look at patch #6. Would you like airq_iv_create(unsigned long bits, unsigned long flags) to take a struct channel_subsystem argument? Regards, Halil