Re: [RFC] Add BPF_PROG_TYPE_CGROUP_IOCTL

[Alex Deucher <alexdeucher@gmail.com>]

On Fri, May 7, 2021 at 12:31 PM Alex Deucher <alexdeucher@gmail.com> wrote:
>
> On Fri, May 7, 2021 at 12:26 PM Daniel Vetter <daniel@ffwll.ch> wrote:
> >
> > On Fri, May 07, 2021 at 12:19:13PM -0400, Alex Deucher wrote:
> > > On Fri, May 7, 2021 at 12:13 PM Daniel Vetter <daniel@ffwll.ch> wrote:
> > > >
> > > > On Fri, May 07, 2021 at 11:33:46AM -0400, Kenny Ho wrote:
> > > > > On Fri, May 7, 2021 at 4:59 AM Daniel Vetter <daniel@ffwll.ch> wrote:
> > > > > >
> > > > > > Hm I missed that. I feel like time-sliced-of-a-whole gpu is the easier gpu
> > > > > > cgroups controler to get started, since it's much closer to other cgroups
> > > > > > that control bandwidth of some kind. Whether it's i/o bandwidth or compute
> > > > > > bandwidht is kinda a wash.
> > > > > sriov/time-sliced-of-a-whole gpu does not really need a cgroup
> > > > > interface since each slice appears as a stand alone device.  This is
> > > > > already in production (not using cgroup) with users.  The cgroup
> > > > > proposal has always been parallel to that in many sense: 1) spatial
> > > > > partitioning as an independent but equally valid use case as time
> > > > > sharing, 2) sub-device resource control as opposed to full device
> > > > > control motivated by the workload characterization paper.  It was
> > > > > never about time vs space in terms of use cases but having new API for
> > > > > users to be able to do spatial subdevice partitioning.
> > > > >
> > > > > > CU mask feels a lot more like an isolation/guaranteed forward progress
> > > > > > kind of thing, and I suspect that's always going to be a lot more gpu hw
> > > > > > specific than anything we can reasonably put into a general cgroups
> > > > > > controller.
> > > > > The first half is correct but I disagree with the conclusion.  The
> > > > > analogy I would use is multi-core CPU.  The capability of individual
> > > > > CPU cores, core count and core arrangement may be hw specific but
> > > > > there are general interfaces to support selection of these cores.  CU
> > > > > mask may be hw specific but spatial partitioning as an idea is not.
> > > > > Most gpu vendors have the concept of sub-device compute units (EU, SE,
> > > > > etc.); OpenCL has the concept of subdevice in the language.  I don't
> > > > > see any obstacle for vendors to implement spatial partitioning just
> > > > > like many CPU vendors support the idea of multi-core.
> > > > >
> > > > > > Also for the time slice cgroups thing, can you pls give me pointers to
> > > > > > these old patches that had it, and how it's done? I very obviously missed
> > > > > > that part.
> > > > > I think you misunderstood what I wrote earlier.  The original proposal
> > > > > was about spatial partitioning of subdevice resources not time sharing
> > > > > using cgroup (since time sharing is already supported elsewhere.)
> > > >
> > > > Well SRIOV time-sharing is for virtualization. cgroups is for
> > > > containerization, which is just virtualization but with less overhead and
> > > > more security bugs.
> > > >
> > > > More or less.
> > > >
> > > > So either I get things still wrong, or we'll get time-sharing for
> > > > virtualization, and partitioning of CU for containerization. That doesn't
> > > > make that much sense to me.
> > >
> > > You could still potentially do SR-IOV for containerization.  You'd
> > > just pass one of the PCI VFs (virtual functions) to the container and
> > > you'd automatically get the time slice.  I don't see why cgroups would
> > > be a factor there.
> >
> > Standard interface to manage that time-slicing. I guess for SRIOV it's all
> > vendor sauce (intel as guilty as anyone else from what I can see), but for
> > cgroups that feels like it's falling a bit short of what we should aim
> > for.
> >
> > But dunno, maybe I'm just dreaming too much :-)
>
> I don't disagree, I'm just not sure how it would apply to SR-IOV.
> Once you've created the virtual functions, you've already created the
> partitioning (regardless of whether it's spatial or temporal) so where
> would cgroups come into play?

For some background, the SR-IOV virtual functions show up like actual
PCI endpoints on the bus, so SR-IOV is sort of like cgroups
implemented in hardware.  When you enable SR-IOV, the endpoints that
are created are the partitions.

Alex

>
> Alex
>
> > -Daniel
> >
> > > Alex
> > >
> > > >
> > > > Since time-sharing is the first thing that's done for virtualization I
> > > > think it's probably also the most reasonable to start with for containers.
> > > > -Daniel
> > > > --
> > > > Daniel Vetter
> > > > Software Engineer, Intel Corporation
> > > > http://blog.ffwll.ch
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> >
> > --
> > Daniel Vetter
> > Software Engineer, Intel Corporation
> > http://blog.ffwll.ch