Re: [Qemu-devel] [RFC PATCH 0/8] MemoryRegion and FlatView refcounting, replace hostmem with memory_region_find

[Paolo Bonzini <pbonzini@redhat.com>]

Il 08/05/2013 08:20, liu ping fan ha scritto:
> On Mon, May 6, 2013 at 10:25 PM, Paolo Bonzini <pbonzini@redhat.com> wrote:
>> Hi,
>>
>> this is an alternative approach to refactoring of dataplane's HostMem
>> code.  Here, I take Ping Fan's idea of RCU-style updating of the
>> region list and apply it to the AddressSpace's FlatView.  With this
> 
> In fact, I am worrying about the priority of MemoryListener, if it is
> true, then we should drop RCU-style idea.

You mean in hostmem, or in general as in this patch?  Note that this
patch releases the old FlatView at the end of all MemoryListener operations.

Paolo

> Also if it is true, there is
> already a bug with hostmem listener. It should use region_del, not
> region_nop to reconstruct the local view. But just let me have a deep
> thinking.
> 
> Regards,
> Pingfan
>> change, dataplane can simply use memory_region_find instead of
>> hostmem.
>>
>> This is a somewhat larger change, but I prefer it for two reasons.
>>
>> 1) it splits the task of adding BQL-less memory dispatch in two parts,
>>    tacking memory_region_find first (which is simpler because locking
>>    is left to the caller).
>>
>> 2) HostMem duplicates a lot of the FlatView logic, and adding the
>>    RCU-style update in FlatView benefits everyone.
>>
>> The missing ingredients here are:
>>
>> 1) remember and unreference the MemoryRegions that are used in
>>    a vring entry.  In order to implement this, it is probably simpler
>>    to change vring.c to use virtio.c's VirtQueueElement data structure.
>>    We want something like that anyway in order to support migration.
>>
>> 2) add an owner field to MemoryRegion, and set it for all MemoryRegions
>>    for hot-unpluggable devices.  In this series, ref/unref are stubs.
>>
>> For simplicity I based the patches on my IOMMU rebase.  I placed the
>> tree at git://github.com/bonzini/qemu.git, branch iommu.
>>
>> Paolo
>>
>> Paolo Bonzini (8):
>>   memory: add ref/unref calls
>>   exec: check MRU in qemu_ram_addr_from_host
>>   memory: return MemoryRegion from qemu_ram_addr_from_host
>>   memory: ref/unref memory across address_space_map/unmap
>>   memory: access FlatView from a local variable
>>   memory: use a new FlatView pointer on every topology update
>>   memory: add reference counting to FlatView
>>   dataplane: replace hostmem with memory_region_find
>>
>>  exec.c                                |   63 +++++++++---
>>  hw/core/loader.c                      |    1 +
>>  hw/display/exynos4210_fimd.c          |    6 +
>>  hw/display/framebuffer.c              |   10 +-
>>  hw/i386/kvm/ioapic.c                  |    2 +
>>  hw/i386/kvmvapic.c                    |    1 +
>>  hw/misc/vfio.c                        |    2 +
>>  hw/virtio/dataplane/Makefile.objs     |    2 +-
>>  hw/virtio/dataplane/hostmem.c         |  176 ---------------------------------
>>  hw/virtio/dataplane/vring.c           |   56 +++++++++--
>>  hw/virtio/vhost.c                     |    2 +
>>  hw/virtio/virtio-balloon.c            |    1 +
>>  hw/xen/xen_pt.c                       |    4 +
>>  include/exec/cpu-common.h             |    2 +-
>>  include/exec/memory.h                 |    9 ++
>>  include/hw/virtio/dataplane/hostmem.h |   57 -----------
>>  include/hw/virtio/dataplane/vring.h   |    3 +-
>>  kvm-all.c                             |    2 +
>>  memory.c                              |  142 +++++++++++++++++++++-----
>>  target-arm/kvm.c                      |    2 +
>>  target-i386/kvm.c                     |    4 +-
>>  target-sparc/mmu_helper.c             |    1 +
>>  xen-all.c                             |    2 +
>>  23 files changed, 253 insertions(+), 297 deletions(-)
>>  delete mode 100644 hw/virtio/dataplane/hostmem.c
>>  delete mode 100644 include/hw/virtio/dataplane/hostmem.h
>>