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=-8.3 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, INCLUDES_PATCH,MAILING_LIST_MULTI,SIGNED_OFF_BY,SPF_HELO_NONE,SPF_PASS, USER_AGENT_SANE_1 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 35C3CC4BA24 for ; Thu, 27 Feb 2020 12:18:11 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 09E822469B for ; Thu, 27 Feb 2020 12:18:11 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1728970AbgB0MSK (ORCPT ); Thu, 27 Feb 2020 07:18:10 -0500 Received: from mx0b-001b2d01.pphosted.com ([148.163.158.5]:54430 "EHLO mx0a-001b2d01.pphosted.com" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S1728856AbgB0MSJ (ORCPT ); Thu, 27 Feb 2020 07:18:09 -0500 Received: from pps.filterd (m0098419.ppops.net [127.0.0.1]) by mx0b-001b2d01.pphosted.com (8.16.0.42/8.16.0.42) with SMTP id 01RCDabk045572 for ; Thu, 27 Feb 2020 07:18:08 -0500 Received: from e06smtp05.uk.ibm.com (e06smtp05.uk.ibm.com [195.75.94.101]) by mx0b-001b2d01.pphosted.com with ESMTP id 2yedd88n7w-1 (version=TLSv1.2 cipher=AES256-GCM-SHA384 bits=256 verify=NOT) for ; Thu, 27 Feb 2020 07:18:08 -0500 Received: from localhost by e06smtp05.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) Thu, 27 Feb 2020 12:18:03 -0000 Received: from d06av24.portsmouth.uk.ibm.com (d06av24.portsmouth.uk.ibm.com [9.149.105.60]) by b06cxnps4075.portsmouth.uk.ibm.com (8.14.9/8.14.9/NCO v10.0) with ESMTP id 01RCI2AN56492062 (version=TLSv1/SSLv3 cipher=DHE-RSA-AES256-GCM-SHA384 bits=256 verify=OK); Thu, 27 Feb 2020 12:18:02 GMT Received: from d06av24.portsmouth.uk.ibm.com (unknown [127.0.0.1]) by IMSVA (Postfix) with ESMTP id 1B2264203F; Thu, 27 Feb 2020 12:18:02 +0000 (GMT) Received: from d06av24.portsmouth.uk.ibm.com (unknown [127.0.0.1]) by IMSVA (Postfix) with ESMTP id BDA9742047; Thu, 27 Feb 2020 12:18:01 +0000 (GMT) Received: from [9.152.99.203] (unknown [9.152.99.203]) by d06av24.portsmouth.uk.ibm.com (Postfix) with ESMTP; Thu, 27 Feb 2020 12:18:01 +0000 (GMT) Reply-To: mimu@linux.ibm.com Subject: Re: [PATCH] KVM: s390: introduce module parameter kvm.use_gisa To: Cornelia Huck Cc: borntraeger@de.ibm.com, frankja@linux.vnet.ibm.com, kvm@vger.kernel.org, david@redhat.com, thuth@redhat.com, linux-s390@vger.kernel.org References: <20200227091031.102993-1-mimu@linux.ibm.com> <20200227104731.17166768.cohuck@redhat.com> From: Michael Mueller Organization: IBM Date: Thu, 27 Feb 2020 13:19:06 +0100 User-Agent: Mozilla/5.0 (Macintosh; Intel Mac OS X 10.14; rv:68.0) Gecko/20100101 Thunderbird/68.5.0 MIME-Version: 1.0 In-Reply-To: <20200227104731.17166768.cohuck@redhat.com> Content-Type: text/plain; charset=utf-8; format=flowed Content-Language: en-US Content-Transfer-Encoding: 7bit X-TM-AS-GCONF: 00 x-cbid: 20022712-0020-0000-0000-000003AE19A1 X-IBM-AV-DETECTION: SAVI=unused REMOTE=unused XFE=unused x-cbparentid: 20022712-0021-0000-0000-00002206388B Message-Id: <513bde27-2596-bbe5-a9e3-1a788bf04b19@linux.ibm.com> X-Proofpoint-Virus-Version: vendor=fsecure engine=2.50.10434:6.0.138,18.0.572 definitions=2020-02-27_03:2020-02-26,2020-02-27 signatures=0 X-Proofpoint-Spam-Details: rule=outbound_notspam policy=outbound score=0 suspectscore=0 phishscore=0 clxscore=1015 lowpriorityscore=0 priorityscore=1501 impostorscore=0 adultscore=0 bulkscore=0 malwarescore=0 mlxscore=0 spamscore=0 mlxlogscore=999 classifier=spam adjust=0 reason=mlx scancount=1 engine=8.12.0-2001150001 definitions=main-2002270100 Sender: kvm-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: kvm@vger.kernel.org On 27.02.20 10:47, Cornelia Huck wrote: > On Thu, 27 Feb 2020 10:10:31 +0100 > Michael Mueller wrote: > >> The boolean module parameter "kvm.use_gisa" controls if newly >> created guests will use the GISA facility if provided by the >> host system. The default is yes. >> >> # cat /sys/module/kvm/parameters/use_gisa >> Y >> >> The parameter can be changed on the fly. >> >> # echo N > /sys/module/kvm/parameters/use_gisa >> >> Already running guests are not affected by this change. >> >> The kvm s390 debug feature shows if a guest is running with GISA. >> >> # grep gisa /sys/kernel/debug/s390dbf/kvm-$pid/sprintf >> 00 01582725059:843303 3 - 08 00000000e119bc01 gisa 0x00000000c9ac2642 initialized >> 00 01582725059:903840 3 - 11 000000004391ee22 00[0000000000000000-0000000000000000]: AIV gisa format-1 enabled for cpu 000 >> ... >> 00 01582725059:916847 3 - 08 0000000094fff572 gisa 0x00000000c9ac2642 cleared > > Maybe log something as well if it is off due to this kernel parameter? There is also no message when the host does not support it. > >> >> In general, that value should not be changed as the GISA facility >> enhances interruption delivery performance. >> >> A reason to switch the GISA facility off might be a performance >> comparison run or debugging. >> >> Signed-off-by: Michael Mueller >> --- >> arch/s390/kvm/kvm-s390.c | 8 +++++++- >> 1 file changed, 7 insertions(+), 1 deletion(-) >> >> diff --git a/arch/s390/kvm/kvm-s390.c b/arch/s390/kvm/kvm-s390.c >> index d7ff30e45589..5c2081488024 100644 >> --- a/arch/s390/kvm/kvm-s390.c >> +++ b/arch/s390/kvm/kvm-s390.c >> @@ -184,6 +184,11 @@ static u8 halt_poll_max_steal = 10; >> module_param(halt_poll_max_steal, byte, 0644); >> MODULE_PARM_DESC(halt_poll_max_steal, "Maximum percentage of steal time to allow polling"); >> >> +/* if set to true, the GISA will be initialized and used if available */ >> +static bool use_gisa = true; >> +module_param(use_gisa, bool, 0644); >> +MODULE_PARM_DESC(use_gisa, "Use the GISA if the host supports it."); > > I probably would have inverted the logic (i.e. introduce a disable_gisa > parameter that is off by default), as you want KVM to use the gisa, > except in special circumstances. Hm, in my opinion "use it := no" is more explicit and natural than "don't use it := yes" > >> + >> /* >> * For now we handle at most 16 double words as this is what the s390 base >> * kernel handles and stores in the prefix page. If we ever need to go beyond >> @@ -2504,7 +2509,8 @@ int kvm_arch_init_vm(struct kvm *kvm, unsigned long type) >> kvm->arch.use_skf = sclp.has_skey; >> spin_lock_init(&kvm->arch.start_stop_lock); >> kvm_s390_vsie_init(kvm); >> - kvm_s390_gisa_init(kvm); >> + if (use_gisa) >> + kvm_s390_gisa_init(kvm); > > I assume we're fine with no gisa but a gib (i.e. doesn't hurt?) The GIB is a host entity and is required for guests with GISA that want to use AP with interruptions in guest. > >> KVM_EVENT(3, "vm 0x%pK created by pid %u", kvm, current->pid); >> >> return 0; > Thanks a lot! Michael