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 C31A6C10F0E for ; Fri, 12 Apr 2019 11:20:59 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 8C2B92171F for ; Fri, 12 Apr 2019 11:20:59 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726772AbfDLLU6 (ORCPT ); Fri, 12 Apr 2019 07:20:58 -0400 Received: from mx0a-001b2d01.pphosted.com ([148.163.156.1]:56950 "EHLO mx0a-001b2d01.pphosted.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726244AbfDLLU6 (ORCPT ); Fri, 12 Apr 2019 07:20:58 -0400 Received: from pps.filterd (m0098396.ppops.net [127.0.0.1]) by mx0a-001b2d01.pphosted.com (8.16.0.27/8.16.0.27) with SMTP id x3CBKcgp121856 for ; Fri, 12 Apr 2019 07:20:57 -0400 Received: from e06smtp04.uk.ibm.com (e06smtp04.uk.ibm.com [195.75.94.100]) by mx0a-001b2d01.pphosted.com with ESMTP id 2rtp7g19f4-1 (version=TLSv1.2 cipher=AES256-GCM-SHA384 bits=256 verify=NOT) for ; Fri, 12 Apr 2019 07:20:56 -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) Fri, 12 Apr 2019 12:20:13 +0100 Received: from b06wcsmtp001.portsmouth.uk.ibm.com (b06wcsmtp001.portsmouth.uk.ibm.com [9.149.105.160]) by b06cxnps4076.portsmouth.uk.ibm.com (8.14.9/8.14.9/NCO v10.0) with ESMTP id x3CBKCPo47251594 (version=TLSv1/SSLv3 cipher=DHE-RSA-AES256-GCM-SHA384 bits=256 verify=OK); Fri, 12 Apr 2019 11:20:12 GMT Received: from b06wcsmtp001.portsmouth.uk.ibm.com (unknown [127.0.0.1]) by IMSVA (Postfix) with ESMTP id 07FC1A4065; Fri, 12 Apr 2019 11:20:12 +0000 (GMT) Received: from b06wcsmtp001.portsmouth.uk.ibm.com (unknown [127.0.0.1]) by IMSVA (Postfix) with ESMTP id 875B5A405F; Fri, 12 Apr 2019 11:20:11 +0000 (GMT) Received: from oc2783563651 (unknown [9.152.224.111]) by b06wcsmtp001.portsmouth.uk.ibm.com (Postfix) with ESMTP; Fri, 12 Apr 2019 11:20:11 +0000 (GMT) Date: Fri, 12 Apr 2019 13:20:10 +0200 From: Halil Pasic To: Sebastian Ott 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: References: <20190404231622.52531-1-pasic@linux.ibm.com> <20190404231622.52531-5-pasic@linux.ibm.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: 19041211-0016-0000-0000-0000026E1957 X-IBM-AV-DETECTION: SAVI=unused REMOTE=unused XFE=unused x-cbparentid: 19041211-0017-0000-0000-000032CA54E9 Message-Id: <20190412132010.3c74cb63@oc2783563651> X-Proofpoint-Virus-Version: vendor=fsecure engine=2.50.10434:,, definitions=2019-04-12_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=794 adultscore=0 classifier=spam adjust=0 reason=mlx scancount=1 engine=8.0.1-1810050000 definitions=main-1904120074 Sender: kvm-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: kvm@vger.kernel.org On Thu, 11 Apr 2019 20:25:01 +0200 (CEST) Sebastian Ott wrote: > On Fri, 5 Apr 2019, Halil Pasic wrote: > > To support protected virtualization cio will need to make sure the > > memory used for communication with the hypervisor is DMA memory. > > > > Let us introduce a DMA pool to cio that will help us in allocating > > deallocating those chunks of memory. > > > > We use a gen_pool backed with DMA pages to avoid each allocation > > effectively wasting a page, as we typically allocate much less > > than PAGE_SIZE. > > 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)? 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)? 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)? Regards, Halil