Re: [PATCH v2 0/8] Add enlightenments for vGPU

Yu, Zhang
2014-10-22T07:11:03Z

On 10/22/2014 12:51 AM, Daniel Vetter wrote:
> On Tue, Oct 21, 2014 at 06:16:26PM +0200, Daniel Vetter wrote:
>> On Fri, Oct 17, 2014 at 01:37:11PM +0800, Yu Zhang wrote:
>>> Intel GVT-g (previously known as XenGT), is a complete GPU
>>> virtualization solution with mediated pass-through for 4th
>>> generation Intel Core processors - Haswell platform. This
>>> technology presents a virtual full-fledged GPU to each Virtual
>>> Machine (VM). VMs can directly access performance-critical
>>> resources, without intervention from the hypervisor in most
>>> cases, while privileged operations from VMs are trap-and-emulated
>>> at minimal cost. For detail, please refer to
>>> https://01.org/xen/blogs/wangbo85/2014/intel-gvt-gxengt-pubic-release
>>>
>>> This patch set includes necessary code changes when i915 driver
>>> runs inside a VM. Though ideally we can run an unmodified i915
>>> driver in VM, adding such enlightenments can greatly reduce the
>>> virtualization complexity in orders of magnitude. Code changes
>>> for the host side, which includes the actual Intel GVT-g
>>> implementation, were sent out in another patchset.
>>>
>>> The primary change introduced here is to implement so-called
>>> "address space ballooning" technique. XenGT partitions global
>>> graphics memory among multiple VMs, so each VM can directly
>>> access a portion of the memory w/o hypervisor's intervention,
>>> e.g. filling textures and queuing commands. However w/ the
>>> partitioning an unmodified i915 driver would assume a smaller
>>> graphics memory starting from address ZERO, so requires XenGT
>>> core module (vgt) to translate the graphics address between
>>> 'guest view' and 'host view', for all registers and command
>>> opcodes which contain a graphics memory address. To reduce the
>>> complexity, XenGT introduces "address space ballooning", by
>>> telling the exact partitioning knowledge to each guest i915
>>> driver, which then reserves and prevents non-allocated portions
>>> from allocation. Then vgt module only needs to scan and validate
>>> graphics addresses w/o complexity of translation.
>>>
>>> Note: The partitioning of global graphics memory may break some
>>> applications, with large objects in the aperture, because current
>>> userspace assumes half of the aperture usable. That would need
>>> separate fix either in user space (e.g. remove assumption in mesa)
>>> or in kernel (w/ some faulting mechanism).
>>>
>>> The partitioning knowledge is conveyed through a reserved MMIO
>>> range, called PVINFO, which will be architecturally reserved in
>>> future hardware generations. Another information carried through
>>> PVINFO is about the number of fence registers. As a global resource
>>> XenGT also partitions them among VMs.
>>>
>>> Other changes are trivial as optimizations, to either reduce the
>>> trap overhead or disable power management features which don't
>>> make sense in a virtualized environment.
>>>
>>> Yu Zhang (8):
>>> drm/i915: Introduce a PV INFO page structure for Intel GVT-g.
>>> drm/i915: Adds graphic address space ballooning logic
>>> drm/i915: Partition the fence registers for vgpu in i915 driver
>>> drm/i915: Disable framebuffer compression for i915 driver in VM
>>> drm/i915: Add the display switch logic for vgpu in i915 driver
>>> drm/i915: Disable power management for i915 driver in VM
>>> drm/i915: Create vgpu specific write MMIO to reduce traps
>>> drm/i915: Support alias ppgtt in VM if ppgtt is enabled
>>>
>>> drivers/gpu/drm/i915/i915_dma.c | 11 +++
>>> drivers/gpu/drm/i915/i915_drv.h | 12 +++
>>> drivers/gpu/drm/i915/i915_gem.c | 5 +
>>> drivers/gpu/drm/i915/i915_gem_gtt.c | 186 +++++++++++++++++++++++++++++++++++-
>>> drivers/gpu/drm/i915/i915_vgt_if.h | 93 ++++++++++++++++++
>>> drivers/gpu/drm/i915/intel_pm.c | 8 ++
>>> drivers/gpu/drm/i915/intel_uncore.c | 22 +++++
>>> 7 files changed, 334 insertions(+), 3 deletions(-)
>>> create mode 100644 drivers/gpu/drm/i915/i915_vgt_if.h
>>
>> I seem to have two v2 versions of this patch series. Anything changed or
>> why the resend? I didn't see any comment on the older version ...
>
> Well, looked through it anyway. On a high level this looks good for the
> vgt integration for guests. I think we need some polish though still,
> specifically for documentation.
>
> - Please extract all the various intel_vgt_* functions spread all over the
> tree into a new i915_vgt_if.c (or intel_vgt.c, but then the header
> should be changed, too I think).
>
> - Please add kerneldoc to all the functions which are non-static and so
> used by the driver outside of your kernel module.
>
> - Please add a DOC: section detailing some of the high-level design
> considerations of vGT and also put that into the new file. I think in
> the future we should also keep the guest<->host abi revisions in there
> (i.e. the stuff in PV_INFO).
Sure. Thanks!
>
> - Please pull all the new documentation together and integrate it into the
> i915 section of the drm docbook. A good place is probably a new
> subsection "Paravirtualized Guest Support (vGPU)" under the driver core
> section.
How about subsection name "Intel GVT-g Guest Support(vGPU)"? :)
>
> There's quite a few i915 driver subsystems which are already nicely
> documented like this, but I also have a small howto:
>
> http://blog.ffwll.ch/2014/06/documentation-for-drmi915.html
Thanks! This blog helps a lot. :)
>
> Cheers, Daniel
>