From mboxrd@z Thu Jan 1 00:00:00 1970 From: Christian Borntraeger Subject: Re: [PATCH/RFC] KVM: track pid for VCPU only on KVM_RUN ioctl Date: Tue, 19 Aug 2014 12:48:23 +0200 Message-ID: <53F32B77.4030603@de.ibm.com> References: <1407249854-2953-1-git-send-email-borntraeger@de.ibm.com> <53E38193.8060206@redhat.com> <53F30CF3.5030606@de.ibm.com> <53F3187E.6080706@redhat.com> <53F31D35.4010901@de.ibm.com> <53F31E9F.9020402@redhat.com> <53F32005.2060902@de.ibm.com> <53F320E8.3040502@redhat.com> <53F32267.6090106@de.ibm.com> <53F3278D.9070107@redhat.com> Mime-Version: 1.0 Content-Type: text/plain; charset=iso-8859-15 Content-Transfer-Encoding: 7bit Cc: KVM , Gleb Natapov , Rik van Riel , Raghavendra K T , Michael Mueller To: Paolo Bonzini Return-path: Received: from e06smtp12.uk.ibm.com ([195.75.94.108]:50412 "EHLO e06smtp12.uk.ibm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751729AbaHSKse (ORCPT ); Tue, 19 Aug 2014 06:48:34 -0400 Received: from /spool/local by e06smtp12.uk.ibm.com with IBM ESMTP SMTP Gateway: Authorized Use Only! Violators will be prosecuted for from ; Tue, 19 Aug 2014 11:48:32 +0100 Received: from b06cxnps3074.portsmouth.uk.ibm.com (d06relay09.portsmouth.uk.ibm.com [9.149.109.194]) by d06dlp01.portsmouth.uk.ibm.com (Postfix) with ESMTP id 4BE6D17D8059 for ; Tue, 19 Aug 2014 11:50:21 +0100 (BST) Received: from d06av04.portsmouth.uk.ibm.com (d06av04.portsmouth.uk.ibm.com [9.149.37.216]) by b06cxnps3074.portsmouth.uk.ibm.com (8.14.9/8.14.9/NCO v10.0) with ESMTP id s7JAmTQg23724158 for ; Tue, 19 Aug 2014 10:48:29 GMT Received: from d06av04.portsmouth.uk.ibm.com (localhost [127.0.0.1]) by d06av04.portsmouth.uk.ibm.com (8.14.4/8.14.4/NCO v10.0 AVout) with ESMTP id s7JAmSPk013117 for ; Tue, 19 Aug 2014 04:48:29 -0600 In-Reply-To: <53F3278D.9070107@redhat.com> Sender: kvm-owner@vger.kernel.org List-ID: On 19/08/14 12:31, Paolo Bonzini wrote: > Il 19/08/2014 12:09, Christian Borntraeger ha scritto: >>> I'm not sure, this does seem like a workaround for another >>> limitation after all... Gleb? >> >> Yes. We want to get rid of KVM_S390_INITIAL_RESET in QEMU. This comes >> from a time, when we had another userspace prototype for KVM on s390 >> (kuli). Its really a wart that has to go. Its just that we are not >> there yet to remove the call to KVM_S390_INITIAL_RESET. Doing so can >> result in hard to debug errors after reboot, if an interrupt was made >> pending just before reboot that gets delivered in the new instance. >> >> The new way for local interrupt read/write will probably be some >> onereg or syncreg interface with a bitmask register and payload >> registers. We have to solve some concurrency and implemenation issues >> here. > > Yes, I understand; the plan is fine and it's good that it was already on > your todo list. > > But since you acknowledge that KVM_S390_INITIAL_RESET will go, I'm not > sure we want to apply this patch (except for the pid == 0 part, of > course---that one is good). Well, it makes todays QEMU (a lot) faster on s390 bootup with many CPUs. (According to strace on my system the first GET_FPU ioctl takes up to 0.079 sec. With 64 CPUs this sums up to several seconds. But I understand your concern of touching generic KVM code only if really necessary. Let me know if I should send a minimal pid==0 version. (I would prefer the full version, of course). Christian