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


From: liu ping fan
Subject: Re: [Qemu-devel] [RFC PATCH 0/8] MemoryRegion and FlatView refcounting, replace hostmem with memory_region_find
Date: Thu, 9 May 2013 08:53:27 +0800

On Wed, May 8, 2013 at 11:44 PM, Paolo Bonzini <address@hidden> wrote:
> Il 08/05/2013 08:20, liu ping fan ha scritto:
>> On Mon, May 6, 2013 at 10:25 PM, Paolo Bonzini <address@hidden> 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.
>
Both in hostmem and this patch, they all broke the original design of
the  MemoryListener, see notes for priority in code.
I have set out 2 patches to highlight this issue, and have CC you and Stefanha.

Regards,
Pingfan

> 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
>>>
>



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