From mboxrd@z Thu Jan 1 00:00:00 1970 From: Avi Kivity Subject: Re: [PATCHv2] kvm: remove in_range and switch to rwsem for iobus Date: Mon, 29 Jun 2009 12:44:53 +0300 Message-ID: <4A488D15.4060500@redhat.com> References: <20090628193425.GA14204@redhat.com> <4A487D2C.2020007@redhat.com> <20090629092309.GA19167@redhat.com> Mime-Version: 1.0 Content-Type: text/plain; charset=ISO-8859-1; format=flowed Content-Transfer-Encoding: 7bit Cc: Gregory Haskins , kvm@vger.kernel.org, linux-kernel@vger.kernel.org, mtosatti@redhat.com, paulmck@linux.vnet.ibm.com, markmc@redhat.com To: "Michael S. Tsirkin" Return-path: Received: from mx2.redhat.com ([66.187.237.31]:38852 "EHLO mx2.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1757290AbZF2JnT (ORCPT ); Mon, 29 Jun 2009 05:43:19 -0400 In-Reply-To: <20090629092309.GA19167@redhat.com> Sender: kvm-owner@vger.kernel.org List-ID: On 06/29/2009 12:23 PM, Michael S. Tsirkin wrote: > On Mon, Jun 29, 2009 at 11:37:00AM +0300, Avi Kivity wrote: > >> On 06/28/2009 10:34 PM, Michael S. Tsirkin wrote: >> >>> This changes bus accesses to use high-level kvm_io_bus_read/kvm_io_bus_write >>> functions, which utilize read/write semaphore intead of mutex. in_range now >>> becomes unused so it is removed from device ops in favor of read/write >>> callbacks performing range checks internally. >>> >>> This allows aliasing (mostly for in-kernel virtio), as well as better error >>> handling by making it possible to pass errors up to userspace. And it's enough >>> to look at the diffstat to see that it's a better API anyway. >>> >>> While we are at it, document locking rules for kvm_io_device_ops. >>> >>> Note: since the use of the new bus_lock is localized to a small number of >>> places, it will be easy to switch to srcu in the future if we so desire. >>> >>> >> Looks good. But please split into a locking change patch and an API >> change patch (in whatever order makes more sense). >> >> I think you can reuse slots_lock instead of adding a new lock. IIRC >> slots_lock is already taken for read everywhere, so you only need to >> take it for write when registering things. >> > > IMO this will make it harder to convert to rcu down the line. > As it is we just grep for bus_lock and replace with rcu. > While possibly slots_lock can be converted to rcu as well, > let's do it one thing at a time. > We can convert it to rcu indepenently of other things protected by slots_lock; no need to do everything at the same time. -- error compiling committee.c: too many arguments to function