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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: |
Fri, 10 May 2013 08:23:05 +0800 |
On Thu, May 9, 2013 at 10:50 PM, Paolo Bonzini <address@hidden> wrote:
> Il 09/05/2013 02:53, liu ping fan ha scritto:
>> 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 think both hostmem and this patch are fine. The hypervisor is never
> involved, all accesses go through the "old" FlatView and regions cannot
> disappear thanks to ref/unref.
>
Here, we worry about add, not del.
> In fact, we need _more_ RCU-style updates, not less. For BQL-less
> dispatch, address space mapping/translation can race against the
> MemoryListeners in exec.c. To fix this, phys_sections and
> AddressSpaceDispatch need to be reference counted and RCU-ified as well.
>
Agree, I like RCU too.
> Paolo
>
>> 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
>>>>>
>>>
>
- [Qemu-devel] [RFC PATCH 4/8] memory: ref/unref memory across address_space_map/unmap, (continued)
- [Qemu-devel] [RFC PATCH 4/8] memory: ref/unref memory across address_space_map/unmap, Paolo Bonzini, 2013/05/06
- [Qemu-devel] [RFC PATCH 3/8] memory: return MemoryRegion from qemu_ram_addr_from_host, Paolo Bonzini, 2013/05/06
- [Qemu-devel] [RFC PATCH 5/8] memory: access FlatView from a local variable, Paolo Bonzini, 2013/05/06
- [Qemu-devel] [RFC PATCH 6/8] memory: use a new FlatView pointer on every topology update, Paolo Bonzini, 2013/05/06
- [Qemu-devel] [RFC PATCH 7/8] memory: add reference counting to FlatView, Paolo Bonzini, 2013/05/06
- [Qemu-devel] [RFC PATCH 8/8] dataplane: replace hostmem with memory_region_find, Paolo Bonzini, 2013/05/06
- Re: [Qemu-devel] [RFC PATCH 0/8] MemoryRegion and FlatView refcounting, replace hostmem with memory_region_find, liu ping fan, 2013/05/08
Re: [Qemu-devel] [RFC PATCH 0/8] MemoryRegion and FlatView refcounting, replace hostmem with memory_region_find, Stefan Hajnoczi, 2013/05/08
Re: [Qemu-devel] [RFC PATCH 0/8] MemoryRegion and FlatView refcounting, replace hostmem with memory_region_find, Stefan Hajnoczi, 2013/05/08