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Re: [Qemu-devel] [RFC PATCH 0/8] MemoryRegion and FlatView refcounting,
From: |
Paolo Bonzini |
Subject: |
Re: [Qemu-devel] [RFC PATCH 0/8] MemoryRegion and FlatView refcounting, replace hostmem with memory_region_find |
Date: |
Thu, 09 May 2013 16:50:36 +0200 |
User-agent: |
Mozilla/5.0 (X11; Linux x86_64; rv:17.0) Gecko/20130311 Thunderbird/17.0.4 |
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.
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.
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 1/8] memory: add ref/unref calls, (continued)
- [Qemu-devel] [RFC PATCH 1/8] memory: add ref/unref calls, Paolo Bonzini, 2013/05/06
- [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