From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from us-smtp-1.mimecast.com ([205.139.110.61]:54147 "EHLO us-smtp-delivery-1.mimecast.com" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S1727279AbgBLNHn (ORCPT ); Wed, 12 Feb 2020 08:07:43 -0500 Date: Wed, 12 Feb 2020 14:07:29 +0100 From: Cornelia Huck Subject: Re: [PATCH v2 RFC] KVM: s390/interrupt: do not pin adapter interrupt pages Message-ID: <20200212140729.21209127.cohuck@redhat.com> In-Reply-To: References: <567B980B-BDA5-4EF3-A96E-1542D11F2BD4@redhat.com> <20200211092341.3965-1-borntraeger@de.ibm.com> <20200212133908.6c6c9072.cohuck@redhat.com> MIME-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit Sender: linux-s390-owner@vger.kernel.org List-ID: To: Christian Borntraeger Cc: david@redhat.com, Ulrich.Weigand@de.ibm.com, aarcange@redhat.com, akpm@linux-foundation.org, frankja@linux.vnet.ibm.com, gor@linux.ibm.com, imbrenda@linux.ibm.com, kvm@vger.kernel.org, linux-mm@kvack.org, linux-s390@vger.kernel.org, mimu@linux.ibm.com, thuth@redhat.com On Wed, 12 Feb 2020 13:44:53 +0100 Christian Borntraeger wrote: > On 12.02.20 13:39, Cornelia Huck wrote: > [...] > > >> + */ > >> + return 0; > > > > Given that this function now always returns 0, we basically get a > > completely useless roundtrip into the kernel when userspace is trying > > to setup the mappings. > > > > Can we define a new IO_ADAPTER_MAPPING_NOT_NEEDED or so capability that > > userspace can check? > > Nack. This is one system call per initial indicator ccw. This is so seldom > and cheap that I do not see a point in optimizing this. NB that zpci also calls this. Probably a rare event there as well. > > > > This change in behaviour probably wants a change in the documentation > > as well. > > Yep.