From mboxrd@z Thu Jan 1 00:00:00 1970 From: Avi Kivity Subject: Re: [Qemu-devel] [RFC v1] Add declarations for hierarchical memory region API Date: Sun, 22 May 2011 14:36:11 +0300 Message-ID: <4DD8F52B.1070905@redhat.com> References: <1305814352-15044-1-git-send-email-avi@redhat.com> <1305814352-15044-2-git-send-email-avi@redhat.com> <4DD8B103.6080409@redhat.com> Mime-Version: 1.0 Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit Cc: qemu-devel@nongnu.org, kvm@vger.kernel.org To: Blue Swirl Return-path: Received: from mx1.redhat.com ([209.132.183.28]:19762 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1754072Ab1EVLgR (ORCPT ); Sun, 22 May 2011 07:36:17 -0400 In-Reply-To: Sender: kvm-owner@vger.kernel.org List-ID: On 05/22/2011 12:32 PM, Blue Swirl wrote: > >> > +void memory_region_add_coalescing(MemoryRegion *mr, > >> > + target_phys_addr_t offset, > >> > + target_phys_addr_t size); > >> > +/* Disable MMIO coalescing for the region. */ > >> > +void memory_region_clear_coalescing(MemoryRegion *mr); > >> > >> Perhaps the interface could be more generic, like > >> +void memory_region_set_property(MemoryRegion *mr, unsigned flags); > >> +void memory_region_clear_property(MemoryRegion *mr, unsigned flags); > >> > > > > Coalescing is a complex property, not just a boolean attribute. We probably > > will have a number of boolean attributes later, though. > > But what is the difference between adding coalescing to an area and > setting the bit property 'coalescing' to an area? At least what you > propose now is not so complex that it couldn't be handled as a single > bit. Look at the API - add_coalescing() sets the coalescing property on a subrange of the memory region, not the entire region. (motivation - hw/e1000.c). > >> > + * conflicts are resolved by having a higher @priority hide a lower > >> > @priority. > >> > + * Subregions without priority are taken as @priority 0. > >> > + */ > >> > +void memory_region_add_subregion_overlap(MemoryRegion *mr, > >> > + target_phys_addr_t offset, > >> > + MemoryRegion *subregion, > >> > + unsigned priority); > >> > +/* Remove a subregion. */ > >> > +void memory_region_del_subregion(MemoryRegion *mr, > >> > + MemoryRegion *subregion); > >> > >> What would the subregions be used for? > > > > Subregions describe the flow of data through the memory bus. We'd have a > > subregion for the PCI bus, with its own subregions for various BARs, with > > some having subregions for dispatching different MMIO types within the BAR. > > > > This allows, for example, the PCI layer to move a BAR without the PCI device > > knowing anything about it. > > But why can't a first class region be used for that? Subregions are first-class regions. In fact all regions are subregions except the root. It's a tree of regions, each level adding an offset, clipping, and perhaps other attributes, with the leaves providing actual memory (mmio or RAM). -- I have a truly marvellous patch that fixes the bug which this signature is too narrow to contain.