[PATCH 0/2] vhot-net: Use kvm_memslots instead of vhost_memory to translate GPA to HVA

[PATCH 0/2] vhot-net: Use kvm_memslots instead of vhost_memory to translate GPA to HVA

[zanghongyong]

From: Hongyong Zang <zanghongyong@huawei.com>

Vhost-net uses its own vhost_memory, which results from user space (qemu) info,
to translate GPA to HVA. Since kernel's kvm structure already maintains the 
address relationship in its member *kvm_memslots*, these patches use kernel's 
kvm_memslots directly without the need of initialization and maintenance of 
vhost_memory.

Hongyong Zang (2):
  kvm: Introduce get_kvm_from_task
  vhost-net: Use kvm_memslots for address translation

 drivers/vhost/vhost.c    |   53 +++++++++++++++++----------------------------
 include/linux/kvm_host.h |    2 +-
 virt/kvm/kvm_main.c      |   13 +++++++++++
 3 files changed, 34 insertions(+), 34 deletions(-)

Re: [PATCH 0/2] vhot-net: Use kvm_memslots instead of vhost_memory to translate GPA to HVA

[Zang Hongyong]

于 2011/12/16,星期五 15:59, Sasha Levin 写道:
> On Fri, 2011-12-16 at 15:40 +0800, Zang Hongyong wrote:
>> 于 2011/12/16,星期五 15:05, Sasha Levin 写道:
>>> On Fri, 2011-12-16 at 13:32 +0800, zanghongyong@huawei.com wrote:
>>>> From: Hongyong Zang<zanghongyong@huawei.com>
>>>>
>>>> Vhost-net uses its own vhost_memory, which results from user space (qemu) info,
>>>> to translate GPA to HVA. Since kernel's kvm structure already maintains the
>>>> address relationship in its member *kvm_memslots*, these patches use kernel's
>>>> kvm_memslots directly without the need of initialization and maintenance of
>>>> vhost_memory.
>>> Conceptually, vhost isn't aware of KVM - it's just a driver which moves
>>> data from vq to a tap device and back. You can't simply add KVM specific
>>> code into vhost.
>>>
>>> Whats the performance benefit?
>>>
>> But vhost-net is only used in virtualization situation. vhost_memory is 
>> maintained
>> by user space qemu.
>> In this way, the memory relationship can be accquired from kernel 
>> without the
>> need of maintainence of vhost_memory from qemu.
> You can't assume that vhost-* is used only along with qemu/kvm. Just as
> virtio has more uses than just virtualization (heres one:
> https://lkml.org/lkml/2011/10/25/139 ), there are more uses for vhost as
> well.
>
> There has been a great deal of effort to keep vhost and kvm untangled.
> One example is the memory translation it has to do, another one is the
> eventfd/irqfd thing it does just so it could signal an IRQ in the guest
> instead of accessing the guest directly.
>
> If you do see a great performance increase when tying vhost and KVM
> together, it may be worth it to create some sort of an in-kernel
> vhost-kvm bridging thing, but if the performance isn't noticeable we're
> better off just leaving it as is and keeping the vhost code general.
>
Thanks for your explanation.
Since memory layout is seldom changed after guest boots, the situation
manily occurs during initialization. There's no need for vhost-kvm
bridge now.

Re: [PATCH 0/2] vhot-net: Use kvm_memslots instead of vhost_memory to translate GPA to HVA

[Zang Hongyong]

于 2011/12/16,星期五 15:59, Sasha Levin 写道:
> On Fri, 2011-12-16 at 15:40 +0800, Zang Hongyong wrote:
>> 于 2011/12/16,星期五 15:05, Sasha Levin 写道:
>>> On Fri, 2011-12-16 at 13:32 +0800, zanghongyong@huawei.com wrote:
>>>> From: Hongyong Zang<zanghongyong@huawei.com>
>>>>
>>>> Vhost-net uses its own vhost_memory, which results from user space (qemu) info,
>>>> to translate GPA to HVA. Since kernel's kvm structure already maintains the
>>>> address relationship in its member *kvm_memslots*, these patches use kernel's
>>>> kvm_memslots directly without the need of initialization and maintenance of
>>>> vhost_memory.
>>> Conceptually, vhost isn't aware of KVM - it's just a driver which moves
>>> data from vq to a tap device and back. You can't simply add KVM specific
>>> code into vhost.
>>>
>>> Whats the performance benefit?
>>>
>> But vhost-net is only used in virtualization situation. vhost_memory is 
>> maintained
>> by user space qemu.
>> In this way, the memory relationship can be accquired from kernel 
>> without the
>> need of maintainence of vhost_memory from qemu.
> You can't assume that vhost-* is used only along with qemu/kvm. Just as
> virtio has more uses than just virtualization (heres one:
> https://lkml.org/lkml/2011/10/25/139 ), there are more uses for vhost as
> well.
>
> There has been a great deal of effort to keep vhost and kvm untangled.
> One example is the memory translation it has to do, another one is the
> eventfd/irqfd thing it does just so it could signal an IRQ in the guest
> instead of accessing the guest directly.
>
> If you do see a great performance increase when tying vhost and KVM
> together, it may be worth it to create some sort of an in-kernel
> vhost-kvm bridging thing, but if the performance isn't noticeable we're
> better off just leaving it as is and keeping the vhost code general.
>
Thanks for your explanation.
Since memory layout is seldom changed after guest boots, the situation
manily occurs during initialization. There's no need for vhost-kvm
bridge now.

Re: [PATCH 0/2] vhot-net: Use kvm_memslots instead of vhost_memory to translate GPA to HVA

[Sasha Levin]

On Fri, 2011-12-16 at 09:59 +0200, Sasha Levin wrote:
> There has been a great deal of effort to keep vhost and kvm untangled.
> One example is the memory translation it has to do, another one is the
> eventfd/irqfd thing it does just so it could signal an IRQ in the guest
> instead of accessing the guest directly.

Actually, CONFIG_VHOST_NET doesn't even depend on CONFIG_KVM, so your
patch will break build when (CONFIG_VHOST_NET=y && CONFIG_KVM=n).

-- 

Sasha.

Re: [PATCH 0/2] vhot-net: Use kvm_memslots instead of vhost_memory to translate GPA to HVA

[Sasha Levin]

On Fri, 2011-12-16 at 09:59 +0200, Sasha Levin wrote:
> There has been a great deal of effort to keep vhost and kvm untangled.
> One example is the memory translation it has to do, another one is the
> eventfd/irqfd thing it does just so it could signal an IRQ in the guest
> instead of accessing the guest directly.

Actually, CONFIG_VHOST_NET doesn't even depend on CONFIG_KVM, so your
patch will break build when (CONFIG_VHOST_NET=y && CONFIG_KVM=n).

-- 

Sasha.

Re: [PATCH 0/2] vhot-net: Use kvm_memslots instead of vhost_memory to translate GPA to HVA

[Sasha Levin]

On Fri, 2011-12-16 at 15:40 +0800, Zang Hongyong wrote:
> 于 2011/12/16,星期五 15:05, Sasha Levin 写道:
> > On Fri, 2011-12-16 at 13:32 +0800, zanghongyong@huawei.com wrote:
> >> From: Hongyong Zang<zanghongyong@huawei.com>
> >>
> >> Vhost-net uses its own vhost_memory, which results from user space (qemu) info,
> >> to translate GPA to HVA. Since kernel's kvm structure already maintains the
> >> address relationship in its member *kvm_memslots*, these patches use kernel's
> >> kvm_memslots directly without the need of initialization and maintenance of
> >> vhost_memory.
> > Conceptually, vhost isn't aware of KVM - it's just a driver which moves
> > data from vq to a tap device and back. You can't simply add KVM specific
> > code into vhost.
> >
> > Whats the performance benefit?
> >
> But vhost-net is only used in virtualization situation. vhost_memory is 
> maintained
> by user space qemu.
> In this way, the memory relationship can be accquired from kernel 
> without the
> need of maintainence of vhost_memory from qemu.

You can't assume that vhost-* is used only along with qemu/kvm. Just as
virtio has more uses than just virtualization (heres one:
https://lkml.org/lkml/2011/10/25/139 ), there are more uses for vhost as
well.

There has been a great deal of effort to keep vhost and kvm untangled.
One example is the memory translation it has to do, another one is the
eventfd/irqfd thing it does just so it could signal an IRQ in the guest
instead of accessing the guest directly.

If you do see a great performance increase when tying vhost and KVM
together, it may be worth it to create some sort of an in-kernel
vhost-kvm bridging thing, but if the performance isn't noticeable we're
better off just leaving it as is and keeping the vhost code general.

-- 

Sasha.

Re: [PATCH 0/2] vhot-net: Use kvm_memslots instead of vhost_memory to translate GPA to HVA

[Sasha Levin]

On Fri, 2011-12-16 at 15:40 +0800, Zang Hongyong wrote:
> 于 2011/12/16,星期五 15:05, Sasha Levin 写道:
> > On Fri, 2011-12-16 at 13:32 +0800, zanghongyong@huawei.com wrote:
> >> From: Hongyong Zang<zanghongyong@huawei.com>
> >>
> >> Vhost-net uses its own vhost_memory, which results from user space (qemu) info,
> >> to translate GPA to HVA. Since kernel's kvm structure already maintains the
> >> address relationship in its member *kvm_memslots*, these patches use kernel's
> >> kvm_memslots directly without the need of initialization and maintenance of
> >> vhost_memory.
> > Conceptually, vhost isn't aware of KVM - it's just a driver which moves
> > data from vq to a tap device and back. You can't simply add KVM specific
> > code into vhost.
> >
> > Whats the performance benefit?
> >
> But vhost-net is only used in virtualization situation. vhost_memory is 
> maintained
> by user space qemu.
> In this way, the memory relationship can be accquired from kernel 
> without the
> need of maintainence of vhost_memory from qemu.

You can't assume that vhost-* is used only along with qemu/kvm. Just as
virtio has more uses than just virtualization (heres one:
https://lkml.org/lkml/2011/10/25/139 ), there are more uses for vhost as
well.

There has been a great deal of effort to keep vhost and kvm untangled.
One example is the memory translation it has to do, another one is the
eventfd/irqfd thing it does just so it could signal an IRQ in the guest
instead of accessing the guest directly.

If you do see a great performance increase when tying vhost and KVM
together, it may be worth it to create some sort of an in-kernel
vhost-kvm bridging thing, but if the performance isn't noticeable we're
better off just leaving it as is and keeping the vhost code general.

-- 

Sasha.

Re: [PATCH 0/2] vhot-net: Use kvm_memslots instead of vhost_memory to translate GPA to HVA

[Zang Hongyong]

于 2011/12/16,星期五 15:05, Sasha Levin 写道:
> On Fri, 2011-12-16 at 13:32 +0800, zanghongyong@huawei.com wrote:
>> From: Hongyong Zang<zanghongyong@huawei.com>
>>
>> Vhost-net uses its own vhost_memory, which results from user space (qemu) info,
>> to translate GPA to HVA. Since kernel's kvm structure already maintains the
>> address relationship in its member *kvm_memslots*, these patches use kernel's
>> kvm_memslots directly without the need of initialization and maintenance of
>> vhost_memory.
> Conceptually, vhost isn't aware of KVM - it's just a driver which moves
> data from vq to a tap device and back. You can't simply add KVM specific
> code into vhost.
>
> Whats the performance benefit?
>
But vhost-net is only used in virtualization situation. vhost_memory is 
maintained
by user space qemu.
In this way, the memory relationship can be accquired from kernel 
without the
need of maintainence of vhost_memory from qemu.

Re: [PATCH 0/2] vhot-net: Use kvm_memslots instead of vhost_memory to translate GPA to HVA

[Zang Hongyong]

于 2011/12/16,星期五 15:05, Sasha Levin 写道:
> On Fri, 2011-12-16 at 13:32 +0800, zanghongyong@huawei.com wrote:
>> From: Hongyong Zang<zanghongyong@huawei.com>
>>
>> Vhost-net uses its own vhost_memory, which results from user space (qemu) info,
>> to translate GPA to HVA. Since kernel's kvm structure already maintains the
>> address relationship in its member *kvm_memslots*, these patches use kernel's
>> kvm_memslots directly without the need of initialization and maintenance of
>> vhost_memory.
> Conceptually, vhost isn't aware of KVM - it's just a driver which moves
> data from vq to a tap device and back. You can't simply add KVM specific
> code into vhost.
>
> Whats the performance benefit?
>
But vhost-net is only used in virtualization situation. vhost_memory is 
maintained
by user space qemu.
In this way, the memory relationship can be accquired from kernel 
without the
need of maintainence of vhost_memory from qemu.

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Re: [PATCH 0/2] vhot-net: Use kvm_memslots instead of vhost_memory to translate GPA to HVA

[Sasha Levin]

On Fri, 2011-12-16 at 13:32 +0800, zanghongyong@huawei.com wrote:
> From: Hongyong Zang <zanghongyong@huawei.com>
> 
> Vhost-net uses its own vhost_memory, which results from user space (qemu) info,
> to translate GPA to HVA. Since kernel's kvm structure already maintains the 
> address relationship in its member *kvm_memslots*, these patches use kernel's 
> kvm_memslots directly without the need of initialization and maintenance of 
> vhost_memory.

Conceptually, vhost isn't aware of KVM - it's just a driver which moves
data from vq to a tap device and back. You can't simply add KVM specific
code into vhost.

Whats the performance benefit?

-- 

Sasha.

Re: [PATCH 0/2] vhot-net: Use kvm_memslots instead of vhost_memory to translate GPA to HVA

[Sasha Levin]

On Fri, 2011-12-16 at 13:32 +0800, zanghongyong@huawei.com wrote:
> From: Hongyong Zang <zanghongyong@huawei.com>
> 
> Vhost-net uses its own vhost_memory, which results from user space (qemu) info,
> to translate GPA to HVA. Since kernel's kvm structure already maintains the 
> address relationship in its member *kvm_memslots*, these patches use kernel's 
> kvm_memslots directly without the need of initialization and maintenance of 
> vhost_memory.

Conceptually, vhost isn't aware of KVM - it's just a driver which moves
data from vq to a tap device and back. You can't simply add KVM specific
code into vhost.

Whats the performance benefit?

-- 

Sasha.

Re: [PATCH 0/2] vhot-net: Use kvm_memslots instead of vhost_memory to translate GPA to HVA

[Takuya Yoshikawa]

(2011/12/16 14:32), zanghongyong@huawei.com wrote:
> From: Hongyong Zang<zanghongyong@huawei.com>
> 
> Vhost-net uses its own vhost_memory, which results from user space (qemu) info,
> to translate GPA to HVA. Since kernel's kvm structure already maintains the
> address relationship in its member *kvm_memslots*, these patches use kernel's
> kvm_memslots directly without the need of initialization and maintenance of
> vhost_memory.

Isn't vhost independent from KVM?

	Takuya

Re: [PATCH 0/2] vhot-net: Use kvm_memslots instead of vhost_memory to translate GPA to HVA

[Takuya Yoshikawa]

(2011/12/16 14:32), zanghongyong@huawei.com wrote:
> From: Hongyong Zang<zanghongyong@huawei.com>
> 
> Vhost-net uses its own vhost_memory, which results from user space (qemu) info,
> to translate GPA to HVA. Since kernel's kvm structure already maintains the
> address relationship in its member *kvm_memslots*, these patches use kernel's
> kvm_memslots directly without the need of initialization and maintenance of
> vhost_memory.

Isn't vhost independent from KVM?

	Takuya

[PATCH 0/2] vhot-net: Use kvm_memslots instead of vhost_memory to translate GPA to HVA

[zanghongyong]

From: Hongyong Zang <zanghongyong@huawei.com>

Vhost-net uses its own vhost_memory, which results from user space (qemu) info,
to translate GPA to HVA. Since kernel's kvm structure already maintains the 
address relationship in its member *kvm_memslots*, these patches use kernel's 
kvm_memslots directly without the need of initialization and maintenance of 
vhost_memory.

Hongyong Zang (2):
  kvm: Introduce get_kvm_from_task
  vhost-net: Use kvm_memslots for address translation

 drivers/vhost/vhost.c    |   53 +++++++++++++++++----------------------------
 include/linux/kvm_host.h |    2 +-
 virt/kvm/kvm_main.c      |   13 +++++++++++
 3 files changed, 34 insertions(+), 34 deletions(-)