Nouveau - Oct 2024 - [RFC 04/29] nvkm/vgpu: set the VF partition count when NVIDIA vGPU is enabled

On 27/09/2024 1.51, Jason Gunthorpe wrote:
> On Sun, Sep 22, 2024 at 05:49:26AM -0700, Zhi Wang wrote:
>> GSP firmware needs to know the number of max-supported vGPUs when
>> initialization.
>>
>> The field of VF partition count in the GSP WPR2 is required to be set
>> according to the number of max-supported vGPUs.
>>
>> Set the VF partition count in the GSP WPR2 when NVKM is loading the GSP
>> firmware and initializes the GSP WPR2, if vGPU is enabled.
> 
> How/why is this different from the SRIOV num_vfs concept?
> 
1) The VF is considered as an HW interface of vGPU exposed to the VMM/VM.

2) Number of VF is not always equal to number of max vGPU supported, 
which depends on a) the size of metadata of video memory space allocated 
for FW to manage the vGPUs. b) how user divide the resources. E.g. if a 
card has 48GB video memory, and user creates two vGPUs each has 24GB 
video memory. Only two VFs are usable even SRIOV num_vfs can be large 
than that.
> The way the SRIOV flow should work is you boot the PF, startup the
> device, then userspace sets num_vfs and you get the SRIOV VFs.
> 
> Why would you want less/more partitions than VFs?
Is there some way to
> consume more than one partition per VF?
No.
> 
> At least based on the commit message this seems like a very poor FW
> interface.
> > Jason

On Sun, Oct 13, 2024 at 06:54:32PM +0000, Zhi Wang
wrote:
> On 27/09/2024 1.51, Jason Gunthorpe wrote:
> > On Sun, Sep 22, 2024 at 05:49:26AM -0700, Zhi Wang wrote:
> >> GSP firmware needs to know the number of max-supported vGPUs when
> >> initialization.
> >>
> >> The field of VF partition count in the GSP WPR2 is required to be
set
> >> according to the number of max-supported vGPUs.
> >>
> >> Set the VF partition count in the GSP WPR2 when NVKM is loading
the GSP
> >> firmware and initializes the GSP WPR2, if vGPU is enabled.
> > 
> > How/why is this different from the SRIOV num_vfs concept?
> > 
> 
> 1) The VF is considered as an HW interface of vGPU exposed to the VMM/VM.
> 
> 2) Number of VF is not always equal to number of max vGPU supported, 
> which depends on a) the size of metadata of video memory space allocated 
> for FW to manage the vGPUs. b) how user divide the resources. E.g. if a 
> card has 48GB video memory, and user creates two vGPUs each has 24GB 
> video memory. Only two VFs are usable even SRIOV num_vfs can be large 
> than that.
But that can't be determine at driver load time, the profiling of the
VFs must happen at run time when the orchestation determins what kind
of VM instance type to run.

Which again gets back to the question of why do you need to specify
the number of VFs at FW boot time? Why isn't it just fully dynamic and
driven on the SRIOV enable?

Jason